CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
Chapter 3
The Geomorphology and Physiographic
Provinces of Central America
JEFFREY S. MARSHALL
“We have been sailing placidly along the
coast…all day - a broad, low land, densely
clad in a green, tropical vegetation…. In full
view are three noble mountains - tall,
symmetrical cones, with sides furrowed with
wrinkle-like valleys veiled in a dreamy,
purple mist that is charming to the eye, and
summits swathed in a grand turban of
rolling clouds. They say these are volcanoes,
but we cannot see any smoke. No matter - it
is a fairy landscape that is very pleasant to
look upon.” Mark Twain, December 1866,
letter written aboard the steamer Columbia
offshore of Guatemala, published in the San
Francisco Alta California, March 15, 1867
3.1
INTRODUCTION
Central America encompasses an intricate mosaic of dynamic landscapes shaped by a
wide range of Earth surface processes. Few other regions worldwide exhibit a
comparable magnitude of geomorphic diversity. Along the length of the Central
American isthmus, highly variable tectonic, lithologic, and climatic domains (Figs. 3.13.3) are superimposed across a small land area (0.4 % of Earth’s total land surface).
The resulting physiography is characterized by a heterogeneous array of geomorphic
provinces (Fig. 3.4), each featuring a distinctive landform assemblage that preserves a
unique history of landscape evolution.
Over 1500 km in length, Central America reaches from the rugged Maya highlands
of Guatemala in the north, to the humid coast ranges of Panama’s Darién isthmus in the
south. This narrow land bridge links the two American continents and forms a critical
divide between the Pacific and Atlantic ocean basins, varying in width from less than
100 km at the Panama Canal, to over 400 km across the interior highlands of Nicaragua
and Honduras. From towering volcanic peaks (>4000 m elevation) to jungle-shrouded
alluvial lowlands, and from rugged tectonic shorelines to passive-margin lagoons,
Central America embodies a geomorphic microcosm of remarkable diversity.
The physiographic architecture of Central America (Fig. 3.4) is defined primarily
by the northwest-trend of the Middle America Trench and Central American Volcanic
Front (Fig. 3.1). These major morphotectonic features were formed by Cenozoic
subduction of the Cocos oceanic plate, and its predecessor, the Farallon plate, beneath
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2 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
the western margin of the Caribbean plate [1-10]. While the northern volcanic front
developed over Paleozoic continental basement of North American origin (Maya and
Chortis blocks), the southern volcanic front formed on the Mesozoic oceanic basement
of the Caribbean plate (Chorotega and Chocó blocks) (Fig. 3.1). Throughout the
Cenozoic, this first-order contrast in basement lithology has been overprinted with a
diverse suite of rock formations (Fig. 3.2) generated in a variety of tectonic settings,
including volcanic cordilleras, fore-arc and trench-slope basins, alluvial plains and
deltas, intra-arc rift valleys, fold-and-thrust belts, highland plateaus, and carbonate
platforms.
Figure 3.1. Tectonic map of Central America, showing the regional geometry of tectonic plates
and basement blocks. Plate names are in white boxes (North American, Caribbean, Cocos,
Nazca, and Panama). Large arrows show plate motions relative to Caribbean plate. Active
plate boundaries are shown as solid lines (with teeth on upper plate of convergent margins,
and opposing arrows indicating transform motion). Shaded areas show basement blocks
(Maya, Chortis, Chorotega, and Chocó). Dashed lines mark major bathymetric features.
EPR: East Pacific Rise; GSC: Galapagos Spreading Center; PFZ: Panama Fracture Zone;
CCRDB: Central Costa Rica deformed belt; NPDB: North Panama deformed belt; SPDB:
South Panama deformed belt; EPDB: East Panama deformed belt.
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
Active tectonic deformation continues to shape the Central American landscape
along several complex plate-boundary zones (Fig. 3.1). In the north, the MotaguaPolochic fault system cuts across central Guatemala, accommodating sinistral shearing
between the North American and Caribbean plates [11-13]. Along Central America’s
Pacific margin, rapid convergence (7-10 cm/yr) occurs between the Cocos and
Caribbean plates at the Middle America subduction zone, generating large earthquakes
[14-18], active volcanism [19-23], and pronounced upper-plate deformation [24-37].
The oblique suduction of steeply dipping seafloor, produced at the East Pacific Rise,
results in pervasive strike-slip faulting and rifting along the northern Central American
margin [24-27]. In contrast, the flat subduction of rough, hotspot-thickened seafloor,
produced at the Galapagos Spreading Center, drives rapid uplift and crustal shortening
across southern Central America [28-37]. Along the margins of Panama, rapid
deformation occurs in response to collision with South America to the east, and oblique
subduction of the Nazca plate to the south [38-42].
Figure 3.2. Geologic map of Central America, showing the distribution of major rock units
(based on map of R.Weyl [1]).
In addition to contrasting lithologic and tectonic domains, Central America also
hosts a wide array of climatic and ecological zones (Fig. 3.3), ranging from the humid
tropical rainforests of the Caribbean and southern Pacific lowlands, with >4.0 m/yr of
rainfall, to the dry tropical savannahs of the northern Pacific coastal plains, with <1.0
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4 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
m/yr of highly seasonal precipitation [43-45]. Similarly, vegetation zones within
mountainous regions range from the humid cloud forests of volcanic highlands to the
dwarf scrublands of the high-altitude páramo. Dramatic climatic and topographic
gradients juxtapose 4000 m peaks that were glaciated in the Pleistocene [46] in close
proximity to humid lowland basins mantled by thick lateric oxisols [7]. Topographic
extremes coupled with variations in slope aspect, wind direction, and orographic
precipitation result in extraordinarily diverse microclimates, vegetative cover, and soil
types within single mountain ranges.
Figure 3.3. Climate map of Central America, showing the regional distribution of Köppen
Climatic Zones based on average temperature and precipitation (modified from [44]).
As a whole, the Central American isthmus forms a geologically tenuous land
bridge that links the two American continents and creates a topographic divide between
the Atlantic and Pacific Ocean basins. This narrow landmass plays a vital role in
directing the ecological evolution of the Americas [47, 48], and may also profoundly
influence ocean circulation and global climate [49-51]. During the Cenozoic, a diverse
array of landscapes has developed along the isthmus in response to dynamic
interactions between regionally variable rock types, complex plate-boundary tectonics,
and an energetic tropical climate. Central America therefore serves as a unique
laboratory for the study of a wide range of geomorphic processes and consequent
pathways of landscape evolution.
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
This chapter explores the regional geomorphology of Central America and defines
a system of physiographic provinces (Fig. 3.4) that characterizes the overall landscape
diversity of this dynamic region. The chapter is organized into sections that provide an
overview of the characteristic landforms and geomorphic processes that define each of
the physiographic provinces. The first half of the chapter looks at the geomorphic
provinces of northern Central America, and the second half examines those of southern
Central America. Each section provides a brief review of current geomorphic research
within the physiographic provinces. Due to the wide range of possible topics, it is
impractical to cover every aspect of these diverse landscapes. The discussion is
therefore limited to a subset of critical topics that provide a general flavor for the
regional geomorphology of Central America. Several of these topics are explored in
greater detail in the four chapters that follow: Volcanism and volcanic landforms
(Chapter 4), Karst landscapes (Chapter 5), Glacial geology and geomorphology
(Chapter 6), and Coastal morphology and coral reefs (Chapter 7).
Figure 3.4. Map of the physiographic provinces of Central America as defined in this chapter.
Solid lines indicate province boundaries. Numbers on map refer to the list of physiographic
provinces at right. Yucatán platform and Chortis highlands sub-regions: a, Northern pitted
karst plain; b, Southern hilly karst plateau; c, Petén karst plateau and lowlands; d, Eastern
block-faulted coastal plain; e, Central Chortis plateau; f, Western rifted highlands; g, Eastern
dissected plateau; h, Honduran borderlands. Digital elevation model derived from NASA
Shuttle Radar Topography Mission (SRTM) image PIA03364.
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6 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
3.2
GEOMORPHOLOGY OF NORTHERN CENTRAL AMERICA
Northern Central America straddles the boundary between two major crustal domains
(Fig. 3.1), the Maya block of southern Mexico, Belize, and northern Guatemala, and
the Chortis block of southern Guatemala, Honduras, El Salvador, and Nicaragua [5255]. These two basement terranes are juxtaposed across the Motagua-Polochic fault
zone of central Guatemala, which defines the active North American-Caribbean plate
boundary. The lithologic and structural contrast between the Maya and Chortis blocks
(Fig. 3.2) exerts a first-order control on regional geomorphology in northern Central
America. This geomorphic template is in turn affected by active plate-boundary
deformation along both the east-west trending Motagua-Polochic fault zone and the
northwest-trending Middle America convergent margin along the Pacific coast. Late
Cenozoic volcanism, generated by subduction at the Middle America Trench imparts
an additional influence on regional geomorphology.
Both the Maya and Chortis blocks (Fig. 3.1) encompass continental basement
terranes of lower Paleozoic metamorphic and igneous rocks (Fig. 3.2) [52-58]. On the
Maya block to the north, the basement is overlain by a thick sequence of upper
Paleozoic clastic and carbonate sediments, upper Jurassic continental red beds, and
Cretaceous to Eocene carbonate and evaporitic rocks [59-61]. This sequence is exposed
across the Maya block within the Sierra Madre of southeastern Mexico, the northern
highlands of Guatemala, and the vast lowlands of the Yucatán platform. The basement
of the Chortis block, to the south of the Motagua-Polochic fault zone, is overlain by
Mesozoic clastic and carbonate sediments, lower Teritiary red beds, and a thick
sequence of Neogene ignimbrites [59, 62-64]. These rocks are exposed throughout the
Chortis highlands of southern Guatemala, Honduras, and Nicaragua.
While the Maya block has undergone only minor rotation relative to the North
American craton, the allocthonous Chortis block to the south, has experienced
significant southeastward displacement and rotation relative to its original position
northwest of the Maya block. The regional geomorphology of northern Central
America is strongly influenced by the lithologic and structural contrasts between these
two adjacent tectonic blocks.
3.2.1 Maya Highlands Province
The Maya Highlands Province (Fig. 3.4) extends in a broad arc from México’s Sierra
Madre de Chiapas, eastward across the northern Guatemalan Altiplano, to the Maya
mountains of southern Belize. These rugged highlands consist of a series of
morphologically distinct mountain ranges separated by deep fault-controlled canyons
and occasional broad alluvial valleys.
The Maya highlands are developed across a Cretaceous-Paleogene age fold belt
that affects the underlying crystalline basement and its sedimentary cover [1-4]. The
intensity of deformation decreases toward the north, where a near-horizontal section
forms the foundation of the Yucatán carbonate platform. The geomorphology of the
Maya highlands is largely controlled by variations in the lithology and structural grain
of deformed sedimentary rocks and metamorphic basement exposed within a series of
eroding, high-altitude mountain belts [65].
In western Guatemala (Fig. 3.5), the Maya Highlands Province extends across the
border from Mexico’s Sierra Madre massif, forming the northwest-trending
Cuchumatanes range. These rugged mountains encompass several distinct geomorphic
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
sectors, including an extensive high-altitude plateau (>3800 m) that was glaciated
during the Pleistocene [46]. Toward the east, the Maya highlands decrease in elevation,
extending into the Chamá and Santa Cruz ranges of east-central Guatemala (Fig. 3.5).
Along their northern margin, the highlands descend toward the Yucatán platform,
encompassing the Lacandón range (<800 m) of northern Guatemala and the Maya
mountains of southern Belize (<1200 m).
Figure 3.5. Map of the physiographic provinces of northern Central America, showing
significant geomorphic features of Guatemala, El Salvador, and portions of Mexico, Belize,
Honduras, and Nicaragua. Digital elevation model derived from NASA Shuttle Radar
Topography Mission (SRTM) image PIA03364.
3.2.1.1 Cuchumatanes Range
The Cuchumatanes range in northwestern Guatemala (Fig. 3.5) consists of a deeply
dissected, northwest-trending, fault-bounded mountain block. This high-altitude range
(>3800 m maximum elevation) encompasses a thick (>7500 m) section of deformed
upper-Paleozoic to Mesozoic sedimentary rocks overlying a lower Paleozoic
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8 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
metamorphic basement [61]. The Cuchumatanes range exhibits several distinct
geomorphic sub-regions, including a spectacular highland plateau (Altos de los
Cuchumatanes), a rugged mountainous zone of karst topography, and a lower-elevation
area of ridges and valleys developed on metamorphic basement [65].
The Altos de los Cuchumatanes plateau (3400-3800 m elevation), in the core of
the Cuchumatanes range, is formed primarily on a 2500-m-thick section of Cretaceous
limestone and dolomite strata near the top of the Maya highlands sedimentary sequence
[61]. This plateau was glaciated during the Pleistocene, leaving a relict landscape of
striated bedrock, moraines, and outwash plains [46, 66, 67] (also see Chapter 6). The
abrupt margins of the Cuchumatanes plateau correspond with deep canyons developed
along a series of northwest trending faults and folds. The southern edge of the plateau
follows a prominent fault escarpment that separates the Maya highlands sedimentary
section from crystalline basement rocks exposed within the Motagua-Polochic fault
zone to the south (Fig. 3.5).
3.2.1.2 Chamá and Santa Cruz Ranges
The Chamá range of north-central Guatemala (Fig. 3.5) exhibits a complex
mountainous landscape formed over east-west trending folds in the Mesozoic
sedimentary section [65]. Where carbonate rocks outcrop along the fold belt, the
Chamá mountains exhibit an undulating karst topography with scarce surface drainage.
On intervening clastic rocks, the landscape consists of low-relief erosion surfaces
traversed by meandering streams. To the east of the Chamá mountains, the Santa Cruz
range (Fig. 3.5) features a strikingly different mountain landscape of steep northwesttrending ridges cut by deeply-eroded drainages [65]. The drainage divides consist of a
series of orthogonal spurs that extend out from the primary ridges. This morphology is
the product of differential erosion along a system of parallel fractures within the
underlying ultramafic basement rocks [60].
3.2.1.3 Lacandón Range
The Lacandón range (Fig. 3.5) marks the northern edge of the Maya Highlands
Province, extending in a broad arc across Guatemala’s southern Petén region to the
Maya Mountains of Belize. This relatively subdued mountain chain (<800 m elevation)
is formed along an arcuate belt of tightly folded Cretaceous limestone and dolomite
strata (La Libertad Arch) at the southern margin of the Yucatán platform [59]. Rising
above the humid Petén lowlands, the Lacandón range consists of a series of ridges and
valleys that exhibit a rugged karst landscape of abundant sinks, isolated knobs, and
poorly integrated surface drainages [65]. The central Lacandón range also encompasses
some broader low-relief karst uplands with occasional limestone columns and towers.
Along the southern margin of the Lacandón range (Fig. 3.5), an extensive alluviallowland has formed where several major rivers descend out of the higher
Cuchumatanes and Chamá ranges to the south [65]. This broad interior lowland
consists of a network of major flood plains, developed where rapid sedimentation
buried the underlying karst topography.
3.2.1.4 Maya Mountains
The Maya Mountains of Belize (Fig. 3.5) consist of a fault-bounded highland (<1200 m
elevation) that exposes granitic and meta-sedimentary basement rocks within an east-
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
northeast trending synclinorium [57, 58]. This isolated mountain block rises abruptly
above the surrounding lowlands of the Petén region and the Belize coastal plain [65].
River systems draining from the Maya Mountains experience sharp changes in channel
morphology as they cross the steep mountain front that separates deformed crystalline
rocks within the massif from the generally flat lying carbonate platform of the adjacent
lowlands [68]. The coastline east of the Maya Mountains (Fig. 3.5) is characterized by
a series of small deltas constructed of coarse clastic sediments eroded from the
metamorphic and igneous interior of the mountain block [69]. This coastal morphology
differs considerably from the low-relief shorelines to the north and south, characterized
by broad estuaries and lagoons fed by stream networks draining carbonate terrains.
3.2.2 Yucatán Platform Province
Extending to the north of the Maya highlands, are the expansive carbonate lowlands of
Petén, northern Belize, and the Yucatán peninsula (Figs. 3.5 and 5.1). Together, these
regions encompass the most extensive karstlands of the North American continent,
covering over 100,000 km2 [70-73] (also see Chapter 5). The Yucatán Platform
Province features a wide array of karst landforms, including sinkholes, cenotes, dry
valleys, cockpits, towers, and elaborate cave networks. This vast carbonate platform
can be subdivided into several distinct physiographic regions (Fig. 3.4), each exhibiting
a characteristic topography and a unique assemblage of karst landforms. The
geomorphic character of each of these areas is closely linked to regional variations in
lithology, structure, and depth to the groundwater table.
3.2.2.1 Northern Pitted Karst Plain
On México’s Yucatán peninsula (Fig. 3.4), a relatively subdued karst landscape is
developed across a flat-lying sequence of Cenozoic marine carbonate rocks [70, 71].
The northern third of the peninsula consists of a low relief pitted karst plain (0-30 m
elevation), characterized by a dense network of sinkholes and cenotes (flooded collapse
pits that access the groundwater table). Efficient subsurface drainage within the pitted
karst plain results in a complete absence of surface streams [74-77]. An extensive
interconnected system of flooded caverns (up to 130 km long) lies beneath the northern
Yucatán lowlands. These caverns formed by aggressive karst dissolution during sea
level low stands of the late Pleistocene. Much of this cave network is now flooded by
stratified groundwater consisting of a lower saline layer, capped by an overlying fresh
water lens.
A prominent 180-km-diameter semicircular alignment of cenotes extends across
the northwestern Yucatán plain. This feature, known as the Ring of Cenotes, represents
a concentric band of enhanced karst permeability that overlies the buried Cretaceousage Chicxulub impact structure [78, 79]. Breaks within extensive coastal dune fields
reveal where the buried impact structure intersects the northwestern coastline of the
Yucatán peninsula. These locations coincide with zones of concentrated groundwater
discharge, as manifested by a high density of springs and flooded coastal wetlands.
3.2.2.2 Southern Hilly Karst Plain
The broad lowland of the northern pitted-karst plain (Fig. 3.4) is bordered along its
southern edge by the prominent northwest-trending La Sierrita de Ticul fault scarp
[70]. The Ticul escarpment consists of an abrupt line of hills that rise up to 50 m above
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10 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
the northern lowlands. This chain of hills forms a distinct ridge that extends for nearly
200 km across the northern Yucatán peninsula, dividing the northern pitted-karst plain
from a hilly karst terrain to the south. The southern hilly-karst plain (Fig. 3.4) covers
much of the Campeche region of the Yucatán peninsula, south of the Ticul escarpment.
This extensive upland (60-80 m elevation) features an irregular karst terrain
characterized by abundant hills with intervening flat-floored depressions (poljes).
Many of these depressions host ephemeral surface streams and contain alluvial
sediments. These basins occasionally flood during the rainy season due to the
inefficient karst drainage in this region.
3.2.2.3 Petén Karst Plateau and Lowlands
In the Petén region of Guatemala, and adjacent portions of northwestern Belize (Figs.
3.4 and 5.1), a distinctly more rugged and heterogeneous karst terrain has formed on an
older sequence of Cretaceous-Paleogene carbonate rocks [65, 80]. The diversity of
karst geomorphology across this region is controlled by local variations in the lithology
and structure of the carbonate bedrock. The karst plateau (<450 m elevation) of
northeastern Petén exhibits a hilly landscape with local relief in excess of several
hundred meters. Surface drainage across the plateau is poorly developed and abundant
sinkholes feed into an extensive network of solution fractures and caverns. Along the
eastern margin of the Petén karst plateau, the landscape exhibits a rugged topography
controlled by underlying normal faults [65, 81]. Local relief can exceed 100 m across
steep scarps formed along the fault-controlled margins of elongate depressions. A
diverse suite of karst landforms occurs in this area, including dry valleys, residual
limestone hills, isolated cockpits, sinkholes, solution corridors, open fissures, and
elaborate cave systems. To the west of the Petén karst plateau, is a humid lowland
region consisting of a vast low-relief alluvial plain covered by large swamps and
numerous lakes [65]. The river network draining this region exhibits an irregular
pattern, interrupted locally by subsurface karst drainage. In some areas, an undulating
topography has formed by karst dissolution and alluvial filling across a series of folds
within the carbonate bedrock.
3.2.2.4 Eastern Block-faulted Coastal Plain
The low-relief coastlines of the Yucatán platform (Fig. 3.4) are characterized by broad
lagoons, mangrove swamps, and seasonally-flooded marshlands. Along the platform’s
east-facing Caribbean coast (including northern Belize), the elongate morphology of
coastal lagoons and lowlands follows a series of north-northeast-trending, faultbounded ridges and depressions [70]. Offshore, an extensive network of fringing reefs
and coral cays has also developed along this structural grain (forming the world's
second longest barrier reef). This horst and graben structure is the result of broadly
distributed transtensional deformation along the North American-Caribbean transform
boundary south of the Yucatán peninsula.
Groundwater discharge along the east coast of the Yucatán peninsula is
concentrated along the north-northeast-trending faults [71, 75, 76]. Mixing of meteoric
groundwater and saline water at the coast results in vigorous karst dissolution,
producing a network of fracture-solution caverns that extend well inland [82-84].
Alignments of cenotes and large lakes occur above these fractures on the coastal plain.
Where these solution fractures intersect the coast, cave collapse results in progressive
enlargement of coves and lagoons. Gradual coalescence of lagoons by wave erosion
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results in the formation of broad, crescent-shaped beaches along the eastern Yucatán
coast.
3.2.3 Motagua Fault Zone Province
A series of major northeast-trending river valleys have developed across central
Guatemala along sinistral strike-slip faults of the North American-Caribbean plate
boundary (Fig. 3.4). This major fault zone separates the Maya and Chortis blocks along
a broad arc extending from the Guatemalan volcanic highlands along the Pacific
margin to the Gulf of Honduras on the Caribbean coast [1-6]. The two most prominent
fault-controlled valleys are those of the Motagua and Polochic rivers (Fig. 3.5), which
drain the interior highlands and flow eastward to the Caribbean Sea [65]. Offshore, the
Motagua and Polochic fault systems merge with the Swan Islands fault, forming a
transform boundary along the northern margin of the Caribbean plate [5, 6].
3.2.3.1 Motagua and Polochic valleys
The lower Motagua and Polochic valleys (Fig. 3.5) contain extensive alluvial plains
that grade eastward into a broad delta on the Gulf of Honduras [65]. A major structural
depression within the lower Polochic valley impounds Lake Izabal (590 km2), the
largest inland body of water in northern Central America. Along both valleys, offset
Quaternary river terraces, gravel fans, and tributary drainages attest to active sinistral
slip along plate boundary faults [12, 13]. The damaging M 7.5 Guatemala earthquake
of 1976 produced left-lateral surface rupture along 230 km of the Motagua fault with
an average of 1.1 m of horizontal displacement and 0.3 m of vertical displacement [11].
Quaternary slip rates of 0.4-1.9 cm/yr have been determined from offset terrace treads
in the Motagua Valley [13].
While the Motagua fault presently accommodates a significant portion of plateboundary slip, the presence of offset late-Neogene fluvial landforms along the Polochic
valley to the north (Fig. 3.5) indicates that the Polochic fault may have been the
primary plate-boundary between 10 and 3 Ma [85]. Prior to this (20-10 Ma), plateboundary deformation may have been localized further to the south along the JocotánChamelcón fault zone in northwestern Honduras. This now inactive fault system has
since been fragmented by east-west extension along a series of north-trending rift
valleys (Fig. 3.5) along the southern margin of the plate-boundary deformation zone
[86-88].
3.2.3.2 Las Minas and Chuacús Ranges
From the broad alluvial valleys on the Gulf of Honduras, the Motagua and Polochic
faults extend westward into the Guatemalan highlands (Fig. 3.5), where they curve to
the northwest along a series of deeply incised valleys. In this region, the plateboundary faults delimit a set of mountain-block slivers that expose lower Paleozoic
metamorphic and igneous basement rocks [56]. The faulted structure of these
crystalline basement rocks largely defines the morphology of sub-parallel ridges and
valleys within the Las Minas and Chuacús ranges (Fig. 3.5) of central Guatemala [65].
To the west, the plate boundary faults extend into Chiapas, México, where deformation
becomes more diffuse within the Sierra Madre massif [89].
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3.2.4 Chortis Volcanic Front Province
The active Chortis volcanic front (Figs. 3.4 and 4.1) encompasses two major,
northwest-trending morphotectonic segments, the Guatemalan Cordillera, formed along
the western margin of the Chortis highlands, and the Salvadoran Cordillera, developed
along the southern boundary faults of the Median Trough graben [1-4, 19-23, 90-92]
(also see Chapter 4). Both of these cordilleras consist of aligned clusters of
stratovolcanoes and calderas localized along transverse faults that cut the Chortis
volcanic front.
3.2.4.1 Guatemalan Cordillera
Central America's highest volcanoes, Tacaná and Tajumulco (>4000 m elevation),
mark the northwestern end of the Chortis volcanic front just south of the Motagua fault
zone (Figs. 3.5 and 4.1). In general, the Guatemalan volcanoes are aligned in clusters
where north to northeast-trending faults intersect the range front of the Teritiary
volcanic highlands [93]. These frontal stratovolcanoes are often flanked by large silicic
calderas [94]. For example, a major volcanic complex in western Guatemala (Figs. 3.5
and 4.1) that includes Santa María, Santiaguito, Santo Tomas, and Cerro Quemado
volcanoes has developed along a transverse, northeast-trending lineament that extends
into the back arc [95-97]. The Quezaltenango Valley north of these stratovolcanoes
may represent an extinct caldera. Similar transverse clusters of frontal stratovolcanoes
flanked by back-arc calderas occur along the entire Chortis volcanic front. Other
volcanic complexes along the Guatemalan cordillera (Figs. 3.5 and 4.1) include the San
Pedro-Atitlán-Tolimán cluster (flanked by Atitlán caldera), the Yepocapa-AcatenangoFuego lineament (flanked by Barahona caldera), and the Agua-Pacaya pair (flanked by
Amatitlán caldera).
Near Guatemala City (Figs. 3.5 and 4.1), the twin stratovolcanoes of Acatenango
and Fuego form spectacular cones that tower 2000 m above the interior highlands and
over 3500 m above the adjacent Pacific coastal plain [98]. Nearby Agua volcano adds a
third hulking peak to the horizon of the modern Guatemalan capital. In 1541, a major
debris flow descended from Agua’s summit to obliterate the colonial capital of Ciudad
Vieja [99]. Throughout the Quaternary, such debris avalanches and lahars have
conspired with occasional ash flows to construct a broad landscape of debris aprons
that extend outward from the Guatemalan volcanoes and on to the Pacific coastal plain
below (Figs. 3.5 and 4.1). The potential for similar events in the future represents a
significant geologic hazard for the people of Guatemala [100].
3.2.4.2 Salvadoran Cordillera
In El Salvador, the active volcanic front is aligned along the southern boundary faults
of the Median Trough (Fig. 3.5), an elongate structural basin at the northwestern end of
the Nicaraguan Depression. Similar to Guatemala, the Salvadoran volcanoes are
localized where tranverse faults intersect the trough [20-23].
In western El Salvador (Figs. 3.5 and 4.1), the Izalco and Santa Ana
stratovolcanoes occur within a large, fault-controlled volcanic complex that also
includes the Coatepeque caldera [101]. This volcanic cluster is the source of a series of
Quaternary andesitic ignimbrites that extend northward into the Median Trough. Late
Pleistocene edifice collapse at Santa Ana volcano unleashed a massive debris
avalanche that traveled over 50 km to the south into the Pacific Ocean [102]. Like
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
Guatemala, the populated lowlands of El Salvador face a significant threat from debris
avalanches and lahars generated by gravitational failure along the volcanic front [103106].
San Salvador volcano, adjacent to the country’s capital city (Figs. 3.5 and 4.1),
consists of multiple remnants of Quaternary eruptive centers, including a large central
crater (El Boquerón), and several surrounding peaks [105-107]. The nearby Ilopango
caldera forms a large lake-filled basin created by a series of major collapse events that
generated widespread tephra deposits found throughout central El Salvador [108, 109].
Southeast of Ilopango caldera (Figs. 3.5 and 4.1), San Vicente volcano consists of a
broad composite mass of two overlapping stratocones [103]. A late Quaternary debris
avalanche and lahar deposit forms a swath of hummocky terrain that extends 25 km to
the southeast of the volcano, reaching the Lempa river on the coastal plain.
Near the southern end of the Chortis volcanic front (Figs. 3.5 and 4.1), San Miguel
volcano forms an imposing composite cone that rises over 2000 m above the lowland
coastal plain near the Gulf of Fonseca [104, 110]. As one of the most active volcanoes
in El Salvador, this prominent peak is surrounded by a youthful landscape consisting of
multiple, historic lava flows. Unlike most of the Chortis volcanoes, San Miguel is
composed predominantly of basalt and shows little evidence of prior explosive
eruptions or debris avalanches.
3.2.5 Chortis Fore Arc Province
The Pacific coastal plain of Guatemala and El Salvador (Fig. 3.4) consists of a lowrelief bajada of coalescing alluvial fans that extend up to 70 km seaward of the
volcanic front [111] (also see Chapter 7). This broad alluvial plain is constructed of
volcanic ejecta and clastic sediments delivered by a network of debris-choked rivers
that drain the interior volcanic highlands. In general, coastal topography along the
Chortis fore arc (Fig. 3.5) is relatively subdued, with only minor localized faulting
affecting the Quaternary strata. This low-relief coastal morphology strongly contrasts
with the tectonically active coastlines of the Chorotega fore arc in southern Central
America (Fig. 3.4). In that region, active faulting and rapid uplift have produced abrupt
coastal topography along the rugged coastlines of Costa Rica and Panama.
3.2.5.1 Guatemalan Coastal Plain
The Guatemalan coastal plain (Fig. 3.5) forms a prominent bulge (>200 km long, and
up to 70 km wide) along Central America’s northern Pacific coastline. This extensive
alluvial lowland encompasses a series of overlapping debris fans, consisting of thick
Quaternary sequences of volcaniclastic sands, gravels, pumaceous ash, and lahar
deposits [111]. These materials have been deposited and reworked along a sub-parallel
network of river channels that descend from the adjacent volcanic highlands. The
spectacular stratovolcanoes that tower more than 3500 m above the coastal plain to the
east represent sources for pyroclastic flows, long-run-out lahars, and massive debris
avalanches [100]. Confined within deeply incised drainages along the volcanic front,
such flows are capable of traveling great distances to inundate the coastal plain below.
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14 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
3.2.5.2 Salvadoran Coastal Plain
Although narrower than the Guatemalan coastal plain, the Pacific lowlands of El
Salvador (Fig. 3.5) share a similar geomorphology of coalescing alluvial fans fed by
coarse detritus from the volcanic highlands. In western El Salvador, the coastline
exhibits a prominent headland referred to as the Acajutla peninsula (Fig. 3.5). This
small promontory extends 7 km offshore to its southern tip at Punta Remedios. The
Acajutla peninsula is the product of a massive late Pleistocene debris avalanche
generated by edifice collapse at Santa Ana volcano, 50 km to the north [102]. The
subaerial deposit covers 390 km2 with an additional estimated component of 150 km2
lying offshore. A 10-km-wide swath of hummocky terrain extends from the Acajutla
peninsula up to the source of the debris avalanche on Santa Ana volcano.
Southeast of the Acajutla peninsula (Fig. 3.5), the coastal plain narrows and gives
way to rocky headlands and cliffs cut into resistant Pliocene volcanic rocks of the
Bálsamo range. This rugged volcanic range intersects the coast in a series of
southwest-trending ridges separated by deeply incised linear canyons. To the east, the
Salvadoran coastal plain widens again where a series of rivers that drain the volcanic
front have deposited broad alluvial fans. The most prominent geomorphic feature along
this coastal segment is the massive delta of the Lempa river (Fig. 3.5). This major river
drains a significant portion of the interior Chortis highlands, transporting its massive
sediment load across the Median Trough to the Pacific coast. The resulting, low relief,
alluvial coastline is characterized by a series of elongate barrier islands and spits that
enclose extensive lagoons.
3.2.6 Chortis Highlands Province
The majority of the Chortis block (Fig. 3.4) consists of a broad, dissected, highland
plateau that extends from western Guatemala, across Honduras and El Salvador, to
northern Nicaragua [27, 52-55, 112-114]. This mountainous topography reaches
elevations >1 km and extends up to 400 km behind the active volcanic front. The
Chortis highlands can be divided into four geomorphic sub-regions (Fig. 3.4) [27, 114]:
a high-altitude central massif with concordant erosion surfaces; a western rifted plateau
south of the Motagua-Polochic fault zone; an eastern zone of heavily dissected
mountains facing the Caribbean lowlands; and an area of east-west trending, faultbounded valleys and ridges along the northern coast. The geomorphic contrast between
these subregions reflects variations in lithology, proximity to plate boundaries, and a
strong east-west climatic gradient across the Chortis highlands.
3.2.6.1 Central Chortis Plateau
The core of the Chortis Highlands Province (Figs. 3.4 and 3.5) consists of a
tectonically stable massif of Paleozoic metamorphic basement rocks and an overlying
sequence of folded Cretaceous sediments. Concordant high-altitude erosion surfaces
(700-1000 m elevation) form a relatively level plateau across this region [27]. While
major rivers have incised deep canyons into bedrock, the plateau remains largely intact
with only limited dissection by tributary networks (Fig. 3.5). The central Chortis
plateau (Fig. 3.4) is isolated from the Caribbean Sea and Pacific Ocean, receiving less
rainfall (1.0-1.5 m/yr) than the rifted highlands to the west (>2 m/yr) and the heavily
dissected Caribbean slope to the east (>3 m/yr) [27].
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
Tomographic imaging of the subducting Cocos plate reveals a slab gap extending
the length of the Chortis highlands [27]. Slab break-off during the Miocene and
associated upwelling of buoyant mantle beneath the Caribbean plate may have induced
epeirogenic uplift of the Chortis highlands [27]. This regional-scale uplift, beginning in
the Middle to Late Miocene, led to deep entrenchment of meandering rivers throughout
the region. Vertical meander incision with no lateral migration implies that uplift
proceeded without local faulting or tilting, as a regional event that affected the entire
Chortis highlands [27].
3.2.6.2 Western Rifted Highlands
South of the Motagua-Polochic fault zone (Figs. 3.4 and 3.5), the Chortis highlands of
southern Guatemala and western Honduras are cut by a discontinuous series of small,
north-trending, flat-floored rift valleys of late Miocene to Quaternary age [86]. Early
workers referred to these valleys under the collective term "Honduras Depression" [19,
112]. However, instead of a single continuous feature as this term implies, these
localized, independent rift basins are scattered across a broad area of the western
highlands (Fig. 3.5) stretching from the Guatemala City graben in the west, to the Sula
and Comayagua valleys of Honduras in the east. Rifting across the western Chortis
block is attributed to regional extension in response to eastward movement of the
Caribbean plate south of the arcuate Motagua-Polochic fault zone [27, 86-88, 113,
114]. In a similar fashion, anticlinal folding has occurred north of the MotaguaPolochic fault zone in response to shortening within the southern Maya block [87].
The southwestern margin of the Chortis Highlands Province (Fig. 3.5) overlies a 2
km thick sequence of pyroclastic rocks produced during the middle Miocene ignimbrite
flare-up along the Central American volcanic front [63]. These materials were
deposited across a pre-existing low-relief terrain formed on underlying basement rocks.
This extensive ignimbrite sheet buried earlier drainage networks and reset the
landscape for the development of a new system of low-gradient meandering rivers [27].
The rift basins of the western Chortis highlands cut these deposits, providing a wellconstrained maximum age for rifting (middle Miocene). In many cases, the riftbounding faults also disrupt entrenched river meanders formed during the regional
uplift event that post-dates the ignimbrites.
3.2.6.3 Eastern Dissected Highlands
The eastern Chortis highlands of Honduras and Nicaragua (Fig. 3.4 and 3.6) encompass
a rugged mountain landscape that faces the Caribbean lowlands of the Mosquito Coast
[27]. This region is highly dissected by drainage networks and is traversed by several
major trunk rivers that descend from the interior highlands onto the coastal plain.
These include the high-discharge Patuca, Coco, and Matagalpa rivers (Fig. 3.6), which
transport large volumes of coarse sediment eroded from the uplifted interior. Although
the eastern portion of the highlands overlies the same basement rocks as the central
plateau, a sharp climate gradient toward the Caribbean coast leads to significantly
greater rainfall in this area (more than double the annual precipitation). Deep
weathering and intense erosion have consumed the highland plateau in this region,
leaving a heavily dissected, lower-elevation terrain (average of <500 m) characterized
by steep ridges and deep intervening valleys.
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16 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
3.2.6.4 Honduran Borderlands
The northern margin of the Chortis highlands (Figs. 3.4 and 3.6), east of the rifted
plateau, consists of a zone of east-west trending fault-bounded basins and ranges,
including the Aguan Valley, and the Nombre de Dios and La Esperanza ranges [114].
Five major east-northeast-trending faults traverse this region, forming the boundaries
of elongate mountain blocks. Offset river channels and other geomorphic indicators
suggest that these faults accommodate left-lateral transtension along the northern flank
of the Chortis highlands. Transtensional fault blocks in this area may represent the
onshore extension of normal fault-bounded basins within the offshore Honduran
borderlands south of Swan Island fault zone. The difference in orientation and
kinematics between the north-south oriented rift valleys to the west (Fig. 3.5), and the
east-west oriented basins and ranges to the east (Fig. 3.6), is attributed to variations in
the divergence angle between the Caribbean plate motion vector and the plateboundary fault zone [114].
Figure 3.6. Map of the physiographic provinces of northern Central America, showing
significant geomorphic features of Nicaragua, and portions of Honduras, El Salvador, and
Costa Rica. Digital elevation model derived from NASA Shuttle Radar Topography Mission
(SRTM) image PIA03364.
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
3.2.7 Mosquito Coast Lowlands Province
The Mosquito Coast Lowlands Province (Fig. 3.4) consists of a broad, thickly
vegetated alluvial plain, up to 150 km wide, along the east-facing portion of Central
America's Caribbean coast. With annual precipitation rates of 4-6 m/yr, these humid
lowlands represent one of the wettest regions on Earth. The alluvial plains of the
Mosquito Coast formed during the late Cenozoic atop a coalescing mass of deltaic sand
and gravel deposits derived from the eroded interior highlands to the west [115]. These
deposits may reach a thickness of up to 4500 m in some areas. Neogene uplift of the
Chortis Highlands (Fig. 3.4) resulted in the deep incision of river drainages, producing
a pulse of coarse, clastic sedimentation across the Caribbean lowlands [115].
Progradation of these deltaic materials across the shallow Nicaragua bank offshore has
produced a low-relief, lobate shoreline (Fig. 3.6) characterized by extensive mangrove
swamps, broad tidal lagoons, elongate barrier islands, and scattered coral reefs.
3.2.7.1 Northern Mosquitia
The promontory of Cabo Gracias a Díos (Fig. 3.6) at the Honduras-Nicaragua border
marks the apex of a massive Pliocene-Pleistocene age delta [115]. This extensive
gravel complex is composed of sediments derived from the Coco and Patuca river
watersheds within the Chortis highlands. Pleistocene stream piracy within the
highlands shifted deposition to the north of Cabo Gracias as the Patuca River captured
flow from the paleo-Coco drainage [115]. Rising sea level during the Holocene has
transferred deposition from the distal fan offshore, to a series of smaller nearshore
deltas along the modern coast. The constant interplay between shifting river courses,
fluctuating sea level, and migrating deltas has been instrumental throughout the late
Cenozoic in shaping the broad alluvial plains of the Mosquito Coast.
3.2.7.2 Southern Mosquitia
Along the southern Mosquito Coast (Fig. 3.6), in eastern Nicaragua, a dense network of
low-gradient rivers feed into a series of extensive coastal wetlands and lagoons. These
lagoons are protected behind large barrier spits that generally extend southward from
the mouths of major rivers. Along the southern Nicaraguan coast, the monotonous,
low-relief alluvial plain is disrupted by occasional hills and coastal cliffs formed by
outcrops of Paleogene to Quaternary volcanic rocks [116]. The Azul volcanic field, in
the jungle-covered lowlands west of Pearl lagoon, consists of three well-defined
Holocene cinder cones. Along the coast between Perlas and Monkey points (Fig. 3.6), a
series of prominent cliffs expose resistant basalt flows interbedded with Tertiary
volcaniclastic sediments. Tertiary lavas also form the basement of the offshore Corn
Islands, where coastal cliffs up to 100 m high expose massive basalt flows.
3.2.8 Nicaraguan Depression Province
The Nicaraguan Depression (Fig. 3.4) is a ~50 km wide structural trough that extends
for over 600 km along the length of the active volcanic front from El Salvador, through
Nicaragua, to northern Costa Rica [25, 116]. This elongate basin is generally
interpreted as a half-graben, bounded along its southwestern margin by northweststriking transtensional faults. The basin is most pronounced in Nicaragua where it
contains Central America’s two largest lakes, Lake Nicaragua (Cocibolca) and Lake
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18 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
Managua (Xolotlán). Beginning in the Pliocene, the Nicaraguan volcanic front
migrated toward the Middle America Trench and trench-perpendicular extension
within the upper plate opened the Nicaraguan Depression. Rifting along the Nicaraguan
volcanic front may reflect a late Cenozoic decrease in the plate convergence rate along
the Pacific margin and hinge rollback of the subducting Cocos plate slab.
3.2.8.1 Central Nicaraguan Depression
In central Nicaragua (Fig. 3.6), the floor of the Nicaraguan Depression lies only 50 m
above sea level. Here, the Mateares fault forms a prominent 900-m-high scarp along
the basin’s southwestern margin. Alluvial and volcanic fill within the basin may be up
to 2000 m thick along the base of the Mateares scarp, indicating nearly 3 km of dip slip
since the Pliocene [25]. The northeastern boundary of the Nicaraguan Depression is
generally defined by the 500-m-high mountain front of the interior Chortis highlands
formed on a thick sequence of Tertiary volcanic rocks [116, 117].
Damaging earthquakes in Managua (Fig. 3.6) in 1931 and 1972 resulted from
shallow rupture on northeast-trending, left-lateral, oblique-slip faults within a pullapart basin along the southern shore of Lake Managua [118, 119]. These faults may be
part of a regional system of northeast-trending sinistral faults that accommodate dextral
shear across the Nicaraguan depression between a forearc sliver at the coast and the
interior highlands to the east [26]. These cross-arc transtensional faults exert a firstorder control on the shoreline morphology of Lakes Managua and Nicaragua. They
also may influence the spacing and orientation of volcanic centers along the
Nicaraguan volcanic front [22].
3.2.8.2 Median Trough, El Salvador
From northern Nicaragua, the Nicaraguan Depression extends across the Gulf of
Fonseca (Fig. 3.6), where it continues along a more westerly trend as the Median
Trough of El Salvador (Fig. 3.5). In El Salvador, the topographic expression of the
trough is more subdued than Nicaragua, yet its general structure and stratigraphy are
quite similar. As in Nicaragua, the volcanic front of El Salvador is localized along the
southwestern margin of the trough where transverse faults intersect the basin.
Focal mechanisms for shallow upper-plate earthquakes along the southern
boundary faults of the Median Trough indicate that these structures are predominantly
right-lateral strike-slip faults with minor components of extension [120-122]. These
faults have produced multiple damaging earthquakes throughout El Salvador’s
recorded history [123]. The geomorphic expression of the Median Trough dies out near
the Guatemalan border (Fig. 3.5) where transtensional deformation gives way to pure
dextral slip along the northwest striking Jalpatagua fault [124]. This fault forms a
major topographic scarp that cuts through the southern Guatemalan volcanic front
offseting Neogene deposits [24].
3.2.8.3 Los Guatusos and San Carlos Lowlands, Costa Rica
South of Lake Nicaragua (Fig. 3.4), the Nicaraguan Depression extends into the Los
Guatusos and San Carlos lowlands of the northern Costa Rican back arc (Fig. 3.7).
Here, the depression is buried by a thick sequence of Quaternary alluvium and volcanic
debris shed from Costa Rica’s Guanacaste and Central volcanic cordilleras. Rivers
descending from the volcanic front flow northward across the basin to join the San
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
Juan River (Fig. 3.7). This major river, which defines the border between Nicaragua
and Costa Rica, flows from Lake Nicaragua eastward to the Caribbean Sea. The
southern end of the Nicaraguan Depression in this area coincides with a rapid transition
from extensional to compressional tectonics within the back arc of Costa Rica’s
Central volcanic cordillera [34]. This transition is related to an abrupt change in the
thickness and dip of the subducting Cocos plate beneath central Costa Rica.
3.2.9 Nicaraguan Volcanic Front Province
The Quaternary volcanic front of Nicaragua (Figs. 3.4 and 4.1) has developed along the
floor of the Nicaraguan depression, with most volcanic centers located along its faultcontrolled southwestern margin [19-23, 116] (also see Chapter 4). Beginning at the
solitary Cosigüina volcano on the Gulf of Fonseca (Figs. 3.6 and 4.1), the Nicaraguan
volcanic front extends southward along the Los Marabios Cordillera to the spectacular
stratocone of Momotombo on the shore of Lake Managua. The volcanic chain then
continues southward, past the Apoyeque caldera, to the massive Las Sierras ignimbrite
shield and the calderas of Masaya and Apoyo. The Cocibolca Cordillera (Figs. 3.6 and
4.1), at the southern end of the volcanic front, extends from Mombacho volcano on the
northern shore of Lake Nicaragua to the twin stratovolcanoes of Concepción and
Madera on Ometepe island.
3.2.9.1 Cosigüina Peninsula
The Nicaraguan volcanic front begins at Cosigüina volcano (Figs. 3.6 and 4.1), on the
southern shore of the Gulf of Fonseca [116]. This solitary volcano stands isolated on a
wide promontory that extends outward into the southern gulf from Nicaragua’s
northern coastal plain. Cosigüina consists of a broad, low-elevation, composite cone
(872 m) with a pronounced ancient caldera rim along its northern slope, a young 300m-high summit cone, and a 2-km-wide, prehistoric, lake-filled summit caldera. This
massive composite volcano generated a powerful, explosive eruption in 1835 that sent
pyroclastic flows into the Gulf of Fonseca (Fig. 3.6), and produced ash fall throughout
Central America and as far away as Mexico and Jamaica [125]. This event is now
recognized as one of the Western Hemisphere’s most powerful historic eruptions.
3.2.9.2 Los Marabios Cordillera
The Los Marabios range (Fig. 3.6), southeast of Cosigüina, consists of a densely
spaced series of composite volcanoes that form a prominent divide between the
northern Pacific coastal plain and the Nicaraguan depression [116]. This alignment of
clustered volcanic vents includes the major stratovolcanoes, San Cristobal, Casita,
Telica, Rota, Las Pilas, and Momotombo (Fig. 4.1). The rapidly growing cinder cone
of Cerro Negro represents the newest addition to this range, having erupted a
significant volume of lava and pyroclastic material since the mid-1800s [126, 127].
Momotombo volcano, at the southern end of the Los Marabios range, forms a
spectacular 1300-m-high Holocene stratocone that towers above the northern shore of
Lake Managua (Figs. 3.6 and 4.1).
During Hurricane Mitch in 1998, a rain-triggered landslide (1.6 million m3) from
the summit of Casita volcano (Figs. 3.6 and 4.1) unleashed a devastating lahar (2-4
million m3) that inundated several villages on the volcano’s Pacific flank, killing more
than 2500 people [128]. This volcano has been identified as a potential site for a future
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20 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
sector collapse related to hydrothermal weakening of its summit edifice [129]. Steep
topography, energetic volcanism, and an aggressive tropical climate have conspired
throughout the Quaternary to induce repeated gravitational failure along the
Nicaraguan cordillera. The resulting lahars in combination with pyroclastic flows have
constructed a broad coastal debris apron that extends up to 30 km seaward of the
volcanic front.
3.2.9.3 Apoyeque and Las Sierras Shields
Between Lake Managua and Lake Nicaragua (Figs. 3.6 and 4.1), a series of calderas
and explosion pits occur along the trace of the Mateares fault zone at the southwestern
edge of the Nicaraguan depression [116]. The Apoyeque caldera complex, at the
northern end of this chain, sits within a broad ignimbrite shield that forms the Chiltepe
peninsula on the western shore of Lake Managua (Fig. 3.6). This low-lying (500 m
elevation) volcanic complex includes two large, lake-filled calderas that are the source
of thick Quaternary pyroclastic deposits mantling the surrounding landscape. The
Nejapa-Miraflores alignment, west of the city of Managua (Figs. 3.6 and 4.1), features
a series of explosion pits, fissure vents, and cinder cones along a north-south trend that
marks a right-step along the Nicaraguan volcanic front.
Southeast of Managua, the lake-filled calderas of Masaya and Apoyo occupy a
prominent upland along the escarpment of the Mateares fault (Figs. 3.6 and 4.1). These
two calderas formed during highly explosive pyroclastic eruptions in the late
Quaternary [130-133]. Subsequent activity along the southern margin of Masaya
caldera, has constructed the twin volcanoes of Nindirí and Masaya, both sources of
historic lava flows.
The Masaya and Apoyo calderas (Figs. 3.6 and 4.1) both belong to the massive
Neogene-Quaternary Las Sierras volcanic shield (180 km3), located between Lakes
Nicaragua and Managua [130-133]. The Las Sierras shield (Figs. 3.6 and 4.1) forms an
anomalous, crescent-shaped highland (>900 m elevation) along the central Nicaraguan
volcanic front. This elongate massif consists of a broad, seaward-facing apron of
ignimbrite deposits of Plio-Pleistocene age, produced primarily by unusually explosive
eruptions of mafic magma from the Masaya caldera.
3.2.9.4 Cocibolca Cordillera
The Cocibolca Cordillera (Fig. 3.6) of southern Nicaragua extends southeastward from
the Las Sierras Shield to Ometepe island in Lake Nicaragua. This cordillera consists of
a widely spaced chain of four major volcanoes that form a series of promontories and
islands within Lake Nicaragua. Standing on the northwestern shore of the lake,
Mombacho volcano (Figs. 3.6 and 4.1) is a large stratocone with a jagged profile,
scarred by multiple episodes of edifice collapse during the late Quaternary. These
events unleashed debris avalanches and lahars that form extensive hummocky deposits
in the lowlands surrounding the mountain [134]. These deposits include an adjacent
promontory and group of small islands that extend out into the lake.
Zapatera volcano, southeast of Mombacho, consists of a low-lying volcanic shield
that forms a broad island near the northwestern shore of Lake Nicaragua (Figs. 3.6 and
4.1). This volcano features a 2-km-wide summit caldera with a 300-m-high central lava
dome. To the southeast of Zapatera, the spectacular twin stratovolcanoes of
Concepción and Madera form Ometepe island, located in central Lake Nicaragua (Figs.
3.6 and 4.1). Towering >1600 m above the lake, Concepción is one of Nicaragua’s
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
most active volcanoes, with 25 eruptions recorded in the last 120 years [135]. Recent
lava flows and lahars continue to expand the shoreline of Ometepe island.
3.2.10 Sandino Fore Arc Province
The Sandino fore arc province (Fig. 3.4) extends along the entire Pacific coast of
Nicaragua, from Punta Cosigüina on the Gulf of Fonseca, to Costa Rica's Punta
Descartes just north of the Santa Elena peninsula. This narrow coastal strip lies west of
the Nicaraguan depression and volcanic front. It includes a northern low-relief coastal
plain constructed of volcanic debris shed from the Los Marabios Cordillera (Fig. 3.6),
and a southern cliff-lined coast where Cretaceous-Neogene marine sedimentary rocks
of the Sandino fore-arc basin extend on land in a series of margin-parallel folds [25,
136-139] (also see Chapter 7).
3.2.10.1 Northern Nicaraguan Coast
Nicaragua's northern Pacific coast, between the Gulf of Fonseca and Puerto Sandino
(Fig. 3.6) consists of a low-relief alluvial plain developed on volcaniclastic debris shed
from active volcanoes of the Los Marabios Cordillera. The 1998 Hurricane Mitch
debris flow from Casita volcano ran out on to the coastal plain for nearly 10 km,
producing sediment laden flooding that extended even further along local stream
channels. Similar to the broad volcanic debris aprons of the Chortis fore arc to the
north, the northern Nicaraguan coastal plain faces a significant hazard from highly
mobile volcanic debris flows. The stream networks draining the Los Marabios range,
deliver an abundant supply of volcaniclastic sediment to the coast. This material has
been reworked along this low-relief coastline, forming a system of large estuaries, delta
plains, and barrier beaches.
3.2.10.2 Southern Nicaraguan Coast
In sharp contrast to the northern coastline, Nicaragua's southern Pacific coast (south of
Puerto Sandino) is characterized by a rugged morphology of rocky headlands, sea
cliffs, and pocket bays (Fig. 3.6). The resistant grain of this coastline is controlled by
structures within Cretaceous-Paleogene marine sedimentary rocks of the Sandino Basin
[25, 136-139]. These units outcrop within a series of margin-parallel folds, which
intersect the coastline at oblique angles, resulting in variable resistance to marine
erosion. Along the central Nicaraguan coast, where these folds expose the Neogene
units within the upper section of the Sandino Basin, a basin-and-range topography has
developed along the coastal plain.
A notable geomorphic feature along this coastline is a 10-km-long Middle
Miocene basaltic dike [138] that armors the coastal bluff near the town of El Transito
(Fig. 3.6). This feature extends offshore at El Transito Bay, forming a rock curtain that
constricts the bay entrance. This resistant barrier contributed to unusually high wave
run-up and a large death toll at this site during the 1992 Nicaraguan tsunami.
3.2.10.3 Las Sierras Shield
Between Puerto Sandino and Las Salinas (Fig. 3.6), Quaternary pyroclastic rocks of the
Las Sierras volcanic complex extend seaward to the Pacific coast forming a prominent
convex bulge in the Nicaraguan coastline. A network of deeply incised barrancas is
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22 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
developing on the Pacific slope of the range due to the rapid headward erosion of steep
drainages into these weak volcanic rocks. At the coast, a late Pleistocene marine
terrace, referred to as the La Boquita surface [140], is cut across the Las Sierras ash
flow tuffs and the steeply dipping Cretaceous-Neogene marine sediments of the
Sandino basin.
The Las Sierras tuffs have been correlated with a distinctive ash horizon in
offshore drill cores dated stratigraphically at 135 ka [133]. This age suggests that the
La Boquita marine terrace may have formed during the last interstadial sea level high
stand at 125 ka [140]. This terrace occurs along the coast at elevations of 17-22 m
attesting to active uplift at rates near 0.1 m/k.y. The La Boquita terrace occurs only
along the coastal segment adjacent to the Las Sierras massif (Fig. 3.6), suggesting that
coastal uplift may be related to thermal expansion or erosion-driven isostatic rebound
of the Las Sierras shield.
3.2.10.4 Punta Descartes, Costa Rica
At the southern end of the Sandino fore arc province (Fig. 3.6), offshore folds intersect
the coastline of northwestern Costa Rica forming the Punta Descartes (an anticline) and
adjacent bays (synclines). On Punta Descartes, the west-northwest grain of the ridges
and valleys is controlled by a system of parasitic folds on a broader anticline. Elevated
Holocene shore platforms, beach ridges, and stream terraces record active coastal
emergence on the Descartes headland [141]. Valley-fill terraces within coastal
embayments extend several kilometers inland reaching 15-20 m elevation. Streams
draining to the Bahía de Salinas are incised into these deposits exposing uplifted
shallow bay to intertidal muds overlain by beach ridge sands and fluvial gravels.
Radiocarbon ages for Holocene deposits indicate uplift rates of 2.0-3.5 m/ k.y. [141].
3.3
GEOMORPHOLOGY OF SOUTHERN CENTRAL AMERICA
In contrast to the continental Chortis block to the north (Fig. 3.1), most of southern
Central America consists of a Neogene-Quaternary volcanic belt that overlies
Mesozoic oceanic basement of Caribbean plate origin [1-10, 142]. This region, referred
to as the Chorotega block (Fig. 3.1), includes all of Costa Rica and western Panama.
The boundary between the Chorotega block and the Chortis block to the north is
defined by a major fault lineament extending from Costa Rica's Santa Elena peninsula
(Fig. 3.7), eastward to the Hess Escarpment in the Caribbean Sea (Fig. 3.1). The
geomorphology of the Chortega block reflects a dynamic history of Cenozoic
volcanism and upper-plate deformation influenced by complex tectonics along the
southern Middle America Trench [7-10]. The eastern limit of the Chorotega block is
defined by a basement suture at the Panama Canal Zone that separates it from the
Chocó block beneath eastern Panama [4-6, 142]. The Chocó block (Fig. 3.1) consists
primarily of Mesozoic igneous basement and overlying Tertiary sediments that extend
along Panama’s Darién isthmus and into the northwestern Colombian cordillera.
The Chorotega and Chocó blocks are situated within a region of complex tectonics
between four major converging plates: Caribbean, South America, Cocos, and Nazca
(Fig. 3.1) [4-6]. Active collision between these plates has fragmented their margins into
a system of fault-bounded microplates that accommodate diffuse regional deformation
[142-145] The Panama microplate (or Panama block) extends from the margin of
South America to central Costa Rica and includes portions of the Chocó and Chorotega
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
basement terranes. This rapidly deforming fragment of Caribbean crust is thusting over
the back arc in response to flat subduction of thickened seafloor (Cocos Ridge) in the
west, and collision with the South American craton to the east [34, 38-40].
Fold and thrust belts offshore of both northern and southern Panama (North and
South Panama deformed belts) accommodate active convergence with the Caribbean
and Nazca plates (Fig. 3.1) [39-41, 146, 147]. Thrust faults in western Colombia
(Atrato-Urubá suture zone) [148] and a broad zone of strike-slip faulting in eastern
Panama (East Panama deformed belt) [42] absorb the collision between the Panama
block and South America. The western boundary of the Panama block consists of a
diffuse transpressional fault zone (Central Costa Rica deformed belt) that traverses
Costa Rica from the Caribbean to the Pacific margin [34].
Central Costa Rica has long been recognized as a tectonic segment boundary along
the Middle America convergent margin [20, 149]. An abrupt transition from the steep
subduction of smooth Cocos plate seafloor in the northwest (East Pacific Rise origin),
to the flat subduction of rough, hotspot-thickened seafloor in the southeast (Galapagos
Spreading Center origin) occurs along the Middle America Trench offshore of central
Costa Rica [150-154]. This transition coincides with pronounced changes in subduction
zone seismicity [149, 150], arc volcanism [20-23, 36], and upper-plate
morphotectonics [28-37].
The thickened seafloor offshore of southern Costa Rica includes the Cocos Ridge
and adjacent seamount domain (Fig. 3.1), products of hotspot volcanism along the
Galapagos Spreading Center [151-158]. As this rough, sediment-poor seafloor enters
the subduction zone, the overriding plate margin experiences pronounced subduction
erosion [159-161]. Flat subduction of this hotspot-thickened crust also drives
transpressional faulting along a broad deformation front (Central Costa Rica deformed
belt) that is propagating from the fore arc into the interior of the upper plate [34]. Late
Cenozoic slab flattening led to retreat of the magmatic front away from the Middle
America Trench in central Costa Rica [36], and total extinction of volcanism directly
inboard of the Cocos Ridge in southern Costa Rica [162, 163]. Collision of the Cocos
Ridge with the southern Costa Rican margin generates pronounced uplift and upperplate shortening from the fore arc into the back-arc basin [28-37]. Along the central
Costa Rican margin, subducting seamounts on the northwest ridge flank erode the outer
trench slope [151, 152] and produce corregated uplift of fore-arc fault blocks at the
coast [33-35].
3.3.1 Chorotega Volcanic Front Province
The volcanic front of southern Central America (Figs. 3.4 and 4.1) is segmented into a
series of distinct cordilleras that have evolved in response to variations in the
geometry, tectonics and geochemistry of subduction along the Middle America Trench
[19-23, 36, 162-170] (also see Chapter 4). In Costa Rica, a dynamic history of
Cenozoic tectonics generated a complex volcanic belt that includes the Guanacaste,
Tilarán, Aguacate, Central, and Talamanca cordilleras (Figs. 3.7 and 4.1). In Panama,
Quaternary volcanism has been limited to the Central Cordillera west of the Canal
Zone (Figs. 3.7 and 4.1). Spatial and temporal variations in the subduction system have
led to sharp contrasts in magma chemistry and eruption style along the length of the
Chorotega volcanic front [21-23]. Changes in slab thickness and dip have instigated
episodes of volcanic front migration and rotation, resulting in a complex morphology
of overlapping cordilleras and intervening basins [36, 170]. Each of the volcanic
23
24 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
cordilleras of Costa Rica and Panama exhibits a unique geomorphology and geologic
history [171-177].
Figure 3.7. Map of the physiographic provinces of southern Central America, showing
significant geomorphic features of Costa Rica, and portions of Nicaragua and Panama.
Digital elevation model derived from NASA Shuttle Radar Topography Mission (SRTM)
image PIA03364.
3.3.1.1 Guanacaste Cordillera
The northern segment of the Chorotega volcanic front (Figs. 3.7 and 4.1) consists of a
Quaternary chain of shield-like stratovolcanos known as the Guanacaste Cordillera
[169]. The four primary volcanoes of this chain, Orosí-Cacao, Rincón de la Vieja,
Miravalles, and Tenorio, are constructed of coalescing lava flows and pyroclastic
material emitted from multiple vents. Unlike the Central Cordillera to the south, the
Guanacaste volcanoes each form distinct mountains that rise sharply above a
surrounding low-relief landscape. The gaps between these volcanoes allow for easy
passage of the Trade Winds between the Caribbean and Pacific basins, resulting in an
exceptionally dry climate along Guanacaste's Pacific coast.
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
Two remnant calderas occur along the Guanacaste Cordillera, and a broad
ignimbrite plateau (2000 km2) extends seaward from the base of the chain. Constructed
of silicic tuffs emitted from pre-cordillera vents, the Guanacaste ignimbrites form a
gently undulating plain (Fig. 3.7) that ends in an abrupt 100-150 m high escarpment
near the modern Pacific coast. Rivers draining the cordillera have incised deep
barrancas into the plateau.
The southern outpost of the Guanacaste cordillera is Arenal volcano, a relatively
small (15 km3) and highly active Holocene strato-cone [178-180]. Located behind the
eroded massif of the extinct Tilarán Cordillera (Figs. 3.7 and 4.1), this steep-sided cone
(>1200 m high) rises abruptly above a structural trough in which it has formed. A
deadly pyroclastic blast in 1968 decimated 15-km2 of rainforest on the volcano’s
western flank. Since this event, Arenal has remained in constant activity, unleashing
occasional ash and lava flows that continue to alter the surrounding landscape.
3.3.1.2 Tilarán and Aguacate Cordilleras
The extinct Tilarán and Aguacate ranges (Fig. 3.7) consist of heavily dissected
remnants of stratovolcanoes and calderas composed of Neogene-Quaternary basaltic to
andesitic lavas, breccias, tuffs, and lahar deposits [169, 181, 182]. Hydrothermal
alteration and deep tropical weathering have destabilized the steep slopes of these
ranges, resulting in pervasive landsliding.
Throughout the central Aguacate range (Fig. 3.7), deeply incised linear canyons
have developed along active, northwest-and-northeast-trending faults of the Central
Costa Rica deformed belt [34-36]. The Río Grande de Tárcoles cuts a deep gorge
through the central Aguacate range, connecting rivers of the Central Valley basin (Fig.
3.7) with the Pacific coastal plain to the southwest. Along the Tárcoles gorge and many
of its tributary canyons, resistant ignimbrite deposits form level benches and isolated
hilltops 50-100 m above the valley floor. Bedrock incision rates based on late
Quaternary isotopic ages for the ignimbrites [40], range from 0.1 to 0.5 mm/yr. Several
extinct, bowl-shaped calderas (e.g., Palmares and Atenas) centered along the northern
flank of the Aguacate range may have generated silicic ignimbrites [36, 182].
3.3.1.3 Central Cordillera
The composite shield volcanoes of Costa Rica’s Central Cordillera, Platanar, Poás,
Barva, Irazú, and Turrialba (Figs. 3.7 and 4.1), form an imposing northwest-trending
mountain range, located northeast of the extinct Aguacate Cordillera [169, 181]. With
peak elevations ranging from 2000-3400 m, these massive, broad-shouldered volcanoes
tower above the adjacent low-relief landscape of Costa Rica’s densely populated
Central Valley (Fig. 3.7). These are the largest volcanoes, in both area and volume, of
the entire Central American volcanic front. Their summits exhibit wide calderas with
multiple craters and transverse alignments of parasitic cones [169]. A strong climatic
gradient across the range results in greater weathering and erosion, deeper stream
incision, and more frequent landsliding on the humid Caribbean slope.
Along both flanks of the Central Cordillera (Fig. 3.7), gravitational spreading of
the volcanic massif generates prominent fault-propagation-fold scarps along the base of
the mountains [183]. These structures offset a sequence of Quaternary lava flows, ash
flow tuffs, lahar deposits, and tephra that drape across the volcanic slopes. Streams that
drain the steep slopes of the Central Cordillera have cut a radial network of deeply
incised barrancas into the Quaternary volcanic sequence [36]. These canyons serve as
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26 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
conduits that feed pyroclastic flows, lavas, and lahars toward the adjacent lowlands of
both the Central Valley and Caribbean coastal plain.
3.3.1.4 Central Valley
The elongate Central Valley of Costa Rica (Fig. 3.7) consists of an east-west trending
basin (600-1200 m elevation) situated between the active volcanoes of the Central
Cordillera and the eroding volcanic remnants of the Aguacate range. Throughout the
Quaternary, this highland basin filled with a thick accumulation (>1 km) of andesitic to
dacitic lavas, pyroclastic rocks, lahar deposits, and lacustrine sediments [36, 181, 182].
The floor of the Central Valley (Fig. 3.7) consists of a low-relief upland surface
with deeply incised river canyons cut into the underlying Quaternary volcanic sequence
[35, 36]. These abrupt canyons outline a pervasive network of seismically active,
northeast and northwest trending transcurrent faults that offset Neogene-Quaternary
rock units throughout the Central Valley and adjacent volcanic ranges [34-36, 184186]. In addition to controlling regional drainage patterns, these structures exhibit
abundant geomorphic features associated with active faulting, including abrupt scarps,
compression ridges, sag ponds, and perennial springs.
The active faults of the Central Valley mark the leading edge of the Central Costa
Rica deformed belt [34], a diffuse deformation front that is propagating into the upper
plate in response to shallow subduction of hotspot-thickened seafloor beneath central
Costa Rica. This broad fault zone extends across the central Costa Rican volcanic front
(Fig. 3.1), linking the North Panama deformed belt on the Caribbean coast, with the
Middle America Trench on the Pacific margin. Throughout Costa Rican history, these
faults have produced damaging, shallow-focus earthquakes, including the 1910 event
that destroyed the colonial capital Cartago [187, 188]. Periods of heightened seismic
activity along the Central Costa Rica deformed belt have been documented in
association with large thrust earthquakes centered on both the Pacific and Caribbean
margins [189-192]. This active deformation zone marks the western boundary of the
Panama microplate [30, 34].
The fault-controlled drainage networks of the Central Valley feed into the Tárcoles
gorge, a prominent canyon cut through the eroded highlands of the Aguacate Cordillera
[35, 36]. This precipitous gorge provides a link between Central Valley rivers and the
Pacific coastal plain below. During the Middle-Late Quaternary, the Tárcoles river
breached the Aguacate drainage divide, leading to progressive capture and rerouting of
Central Valley drainage networks toward the Pacific slope [35, 36].
The geomorphic evolution of Costa Rica’s Central Valley and surrounding
volcanic cordilleras (Fig. 3.7) was profoundly affected by changes in Cocos plate
subduction during the late Cenozoic. The propagation of irregular, hotspot-thickened
seafloor down the subduction zone led to a shallowing of the subducting slab and a
progressive retreat of the volcanic front from the Aguacate Cordillera to the Central
Cordillera [36]. This northeastward expansion of the volcanic front resulted in the
formation of the Central Valley basin and a shift in the location of the PacificCaribbean drainage divide. Linkage of the Central Valley drainage with the Pacific
slope established a pathway for spillover of Quaternary pyroclastic flows and lahars
onto the Orotina debris fan at the coast. Retreat of the volcanic front occurred only
onshore of moderately thickened crust of the Cocos plate seamount domain, leading to
formation of the Central Cordillera. Directly inboard of the subducting Cocos Ridge
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
(Fig. 3.1) to the south, volcanism shut off and rapid uplift maintains the drainage divide
along the crest of the Talamanca Cordillera [36].
3.3.1.5 Talamanca Cordillera
Southeast of the Central Valley, the extinct Talamanca Cordillera (Fig. 3.7)
corresponds with a 175 km volcanic gap that extends into western Panama [20-23].
These rugged mountains represent the only area of southern Central America above
4000 m in elevation. Similar in age to the Aguacate Cordillera (Fig. 3.7), the
Talamanca range is composed of a suite of Neogene-Quaternary intrusive (principally
granodiorites) and extrusive rocks (andesites) [162, 163, 166-170]. In contrast to the
Aguacate range however, rapid Quaternary uplift and unroofing caused by Cocos
Ridge subduction has stripped off large volumes of extrusive rock from the Talamanca
range exposing the intrusive core. The highest peaks of this range were glaciated
during the Pleistocene, leaving striking examples of moraines, tarns, and striated
bedrock on mountaintops overlooking thickly vegetated tropical lowlands [46, 193198] (also see Chapter 6).
3.3.1.6 Central Cordillera, Panama
The Talamanca volcanic gap of southern Costa Rica ends at the dormant Barú volcano
(Fig. 3.7) at the western end of Panama's Central Cordillera [163-166]. This imposing
stratovolcano towers above the Pacific coastal plain of western Panama. It features a 6km-wide summit caldera that was breached on its western margin by a major
Quaternary debris-avalanche. Lava flows and lahar deposits on the southwestern flank
of Barú volcano are affected by incipient faults of the Terraba thrust belt, which is
propagating southeastward along the margin in the wake of the migrating Panama
triple junction [199-200]. In addition to Barú, the Panamanian cordillera also features
several other Quaternary volcanoes, including La Yeguada and El Valle [164-166].
Isotopic ages on lava flows, in conjunction with youthful geomorphic features provide
evidence for recent activity at these volcanoes.
3.3.2 Chorotega Fore Arc Province
The Chorotega fore arc (Fig. 3.4) extends along the Pacific coast from Costa Rica's
Santa Elena peninsula in the north (Fig. 3.7), to the Gulf of Panama in the south (Fig.
3.8). This rapidly deforming convergent margin coast is characterized by abrupt
topography [201] and a series of peninsulas and headlands that expose late Mesozoic
oceanic basement rocks [202-205] and overlying pelagic to shallow marine sediments
of Paleogene-Quaternary age [206-208]. These peninsulas and promontories, located in
both Costa Rica and Panama, include Santa Elena, Nicoya, Herradura, Quepos, Osa,
Burica, Soná, and Azuero (Figs. 3.7 and 3.8). Like the adjacent volcanic front, the
Chorotega fore arc is highly segmented with sharp contrasts in structure and coastal
morphology linked to variations in the subducting Cocos and Nazca plates offshore
[28-37] (also see Chapter 7).
Along the Chorotega fore arc (Fig. 3.4), the subducting Cocos and Nazca plates
exhibit dramatic variations in thickness, roughness, dip, and convergence angle that
coincide with sharp contrasts in the style of upper plate deformation. Overall, the
subducting seafloor has minimal sediment cover and, in many areas (e.g., offshore
southern Costa Rica), is anomalously thick with substantial morphologic roughness
27
28 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
[151, 152]. As a result, subduction erosion produces scarring and subsidence along
much of the offshore fore-arc [159-161]. In contrast, however, the subaerial inner fore
arc along the coast has experienced uplift in many areas, consistent with out-ofsequence thrusting or underplating beneath the margin [33, 35, 37].
The overall Quaternary deformation pattern along the Costa Rican coast strongly
reflects the offshore bathymetry associated with the subducting Cocos Ridge (Fig. 3.1)
and seamount domain [29, 33, 35]. In general, Quaternary uplift rates derived from
radiometrically-dated marine and fluvial terraces decrease parallel to the margin,
moving northwestward away from the subducting Cocos Ridge. These rates range from
a maximum of 6-7 m/k.y. astride the ridge in the south, to background rates of <1
m/k.y. above smooth subducting crust in the north. This overall long-wavelength trend
reflects a decrease in upward flexure of the overriding crust as the thickness of the
subducting plate diminishes away from the Cocos Ridge axis.
Shorter-wavelength roughness related to seamounts superimposes local variability
on this background uplift pattern [33]. Along the central Costa Rican Pacific coast (Fig.
3.7), uplift rates vary sharply across a series of margin-perpendicular faults that
segment the coastal fore arc into discrete fault blocks [33-35]. While the central Costa
Rican fore arc exhibits strong segmentation across fault-bounded blocks, the fore arc
region south of Quepos (Fig. 3.7) deforms more uniformly by rapid shortening across
the Fila Costeña fold and thrust belt [37, 109, 200]
3.3.2.1 Santa Elena Peninsula and Papagayo Gulf
The northern Chorotega fore arc (Fig. 3.7) meets the Sandino fore arc of the Chortis
block along an abrupt boundary defined by the Murcielago fault zone on the Santa
Elena peninsula [141, 209]. This structure follows a linear E-W trending valley that
bisects the peninsula along its northern coast forming several prominent bays. The
Murcielago fault zone marks a sharp change in geology and geomorphology from the
northwest-dipping hogback ridges formed on late Cretaceous Sandino Basin marine
sediments in the north, to the peninsula's rugged interior highlands in the south formed
on the Jurassic-Cretaceous ultra-mafic basement of the Santa Elena nappe [162, 202].
The morphology of the rugged shoreline extending southward from the Santa
Elena peninsula to the northen Nicoya peninsula (Fig. 3.7) is determined primarily by
resistant fault-bounded basement outcrops and steep cliffs formed of the overlying
Guanacaste ignimbrites. At Punta Mala along the Bahía Culebra (Fig. 3.7), a surviving
fragment of the ignimbrite mesa maintains steep columnar-jointed cliffs rising from a
foundation of basement rocks. Coastal embayments here preserve a Quaternary fill
wedge of shallow marine sediments that record active uplift [141].
3.3.2.2 Nicoya Peninsula
The Nicoya peninsula (Fig. 3.7) lies along an emergent segment of the Chorotega fore
arc south of the Santa Elena peninsula. Separated from the Costa Rican mainland by
the broad Gulf of Nicoya and Tempisque river basin, this large, rectangular peninsula
covers over 4800 km2 of the outer forearc [171-172]. The Nicoya peninsula’s rugged
Pacific coastline features abundant pocket bays and sandy beaches, bounded by steep,
rocky headlands. Uplifted marine terraces and paleo-beach deposits indicate active
emergence throughout the late Quaternary [210-215]. In contrast, the peninsula’s gulf
coast follows a low-relief alluvial plain with extensive mangrove estuaries. The coastal
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
piedmont along all sides of the Nicoya peninsula rises steeply into a mountainous
interior highland that reaches over 900 m in elevation.
Basement rocks exposed on the Nicoya peninsula consist of the Cretaceous-early
Tertiary Nicoya Complex, an intensely deformed oceanic sequence of pillow basalts,
mafic intrusive rocks, and pelagic sediments [162, 202-205]. Along the margins of the
peninsula, a sequence of upper Cretaceous to Quaternary marine sediments drapes
unconformably across the Nicoya Complex basement [206-208]. These sediments
include Cretaceous-Paleocene turbidites, Eocene deep-water carbonates, Miocene shelf
clastics and a shallowing upward sequence of Plio-Pleistocene shelf sandstones and
conglomerates.
Located only 60 km inboard of the Middle America Trench (Fig. 3.1), the Nicoya
peninsula lies directly above the seismogenic zone [211, 213-215]. This unique
location results in pronounced seismic cycle deformation, which is readily observed
along the peninsula’s shorelines. Coseismic uplift of >1m affected the Nicoya
peninsula’s central Pacific coastline during the M 7.7 subduction earthquake of 1950
[211]. Since that event, interseismic strain has led to notable subsidence along this
same shoreline. Seismicity and GPS data indicate that the peninsula occupies a highpotential seismic gap that is accumulating strain in advance of the next event [216,
217].
A sequence of Quaternary marine and fluvial terraces on the Nicoya peninsula
(Fig. 3.7) provide a record of continuing uplift along this segment of the Chorotega
fore arc [35, 210-215]. High-elevation remnants of a Pliocene-Pleistocene marine
erosion surface (Cerro Azul surface) are preserved within the peninsula's interior
mountain block [210]. Deformation of this surface records differential uplift across a
series of mountain block faults. A lower elevation alluvial terrace (La Mansión surface)
occupies interior river valleys at 4-10 m above local base level [210].
Near Cabo Blanco at the southern tip of the Nicoya peninsula (Fig. 3.7), a
prominent late Pleistocene marine erosion surface (Cobano surface) is cut across
Pliocene-Pleistocene shallow-water sediments and late Cretaceous oceanic basalts [35,
210-215]. This uplifted erosion surface forms a broad dissected mesa between the
interior mountains and abandoned sea cliffs near the coast. The Cobano surface
encompasses at least four distinct Pleistocene marine terrace treads ranging in elevation
from 15 m to 220 m above sea level. Age correlation with late Pleistocene sea level
high stands at 60-215 ka (marine oxygen isotope stages 3-7) indicate net uplift rates of
1.0-2.0 m/k.y. [213-215]. Radiogenic ages (Optically Stimulated Luminescence) for
terrace deposits on the lowest three treads are consistent with sea level correlations,
indicating ages of 65-120 ka (marine oxygen isotope stages 3-5). The Cobano terraces
exhibit a measurable decrease in tread elevation toward the northeast, away from the
Middle America Trench. Uplift and tilting, beginning in the middle to late Pleistocene,
led to emergence of the Nicoya peninsula's southern tip and erosion of the Cobano
terraces during sea level highstands of the late Pleistocene.
An adjacent set of narrow (<1 km), low-lying (<20 m elevation) Holocene terraces
(Cabuya surface) occur between the active shoreline and the abandoned sea cliffs along
the seaward edge of the Pleistocene Cobano surface [211]. These wavecut platforms
have emerged where uplift rates exceed the rate of late Holocene sea level rise.
Radiocarbon dating of 35 samples from fossiliferous, intertidal sand and beach rock
deposits yielded late Holocene ages ranging between 0.3-7.4 ka [35, 211, 212]. Uplift
rates decrease from a maximum of 6.0 m/ky near Cabo Blanco, to <1.0 m/ky along a
20 km length of both the margin-perpendicular and margin-parallel coastlines of the
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30 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
peninsula's southern tip. This trend indicates active rotation of Holocene paleoshorelines toward the north, consistent with the tilt observed on the adjacent
Pleistocene Cobano terraces. Rapid uplift and northward tilting of the Nicoya
Peninsula’s southern tip has been attributed to seamount subduction offshore of the
Cabo Blanco headland [35, 211, 212].
Along the northern coast of the Nicoya peninsula (Fig. 3.7), an additional late
Pleistocene marine erosion surface (Iguanazul surface) is cut across late Cretaceous
seafloor basalts [213-215]. The Iguanazul surface consists of at least three separate
wave-cut treads that preserve paleo-shorelines from 10-32 m in elevation. Age
correlation with late Pleistocene sea level high stands at 80-215 ka (marine oxygen
isotope stages 5-7) indicate net uplift rates of 0.1-0.3 m/k.y. Radiocarbon-dated beach
rock horizons along the active beach yield Holocene ages consistent with recent uplift
at <0.5 m/k.y. [213-215].
While the northern Nicoya peninsula lies onshore of the Cocos plate "smooth
domain", the southern peninsula sits inboard of subducting seamounts of the "rough
domain" (Fig. 3.1). The order-of-magnitude difference in Quaternary uplift rates
between the northern Nicoya peninsula (Iguanazul surface) and the southern peninsula
(Cobano surface) may be linked to sharp contrasts in the roughness, thickness, and dip
of the subducting Cocos plate offshore. Rapid uplift and block rotation of the
peninsula’s southern tip is consistent with seamount subduction along the projected
trend of the Fisher seamount chain [35, 211, 212]. A large subduction earthquake
centered offshore of Cabo Blanco in 1990 (M 7.0) may have ruptured a seamount
asperity, imaged both by aftershock locations and seismic tomography [190, 218].
3.3.2.3 Orotina-Esparza Coast
Along 150 km of coastline south of the Nicoya peninsula (Fig. 3.7), major trunk rivers
draining the inner forearc flow along a system of active, coast-orthogonal faults. These
steep faults segment the inner forearc coastline into seven fault-bounded blocks with
sharply differing Quaternary uplift rates as determined from elevated marine and
fluvial terraces [30, 33-36]. These fault blocks are named (from north to south):
Esparza, Orotina, Herradura, Esterillos, Parrita, and Quepos.
The coastline between the Nicoya Peninsula and the Herradura headland (Fig. 3.7)
consists of a low-relief (<250 m) coastal piedmont (750 km2) along the base of the
extinct Aguacate volcanic range [35, 36, 219]. This region includes the lower drainage
basins of the Barranca, Jesús María, and Tárcoles rivers, which flow southwestward
into the Gulf of Nicoya. These rivers follow fault-controlled valleys incised within
Neogene-Quaternary nearshore sediments, volcaniclastic debris, and pyroclastic
deposits. The Barranca, Jesús María, and Tárcoles faults form the boundaries of the
Esparza and Orotina fault blocks.
The low-lying Orotina fault block (Fig. 3.7) between the Jesús María and Tárcoles
rivers is covered by a >100 m thick Quaternary sequence of lahar deposits, ash flows,
volcaniclastic sands, and fluvial gravels [35, 36, 219]. During the early Quaternary, a
series of eruption-generated lahars descended from the volcanic front onto the coastal
plain, forming the framework of a 25-km-wide debris fan (Orotina fan). Rapid
headward erosion across the Aguacate drainage divide led to stream capture within the
Central Valley (Fig. 3.7) and deep incision of the modern drainage system funneling
toward the Tárcoles gorge. This shift in the location of the Pacific-Caribbean drainage
divide opened a pathway for pyroclastic flows to spill over onto the Orotina debris fan
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
at the Pacific coast. Meandering paleo-channels of the Tárcoles river are preserved
across the fan surface as inverted topographic ridges of welded tuff overlying river
gravels [35, 36].
The interior of the Orotina fault block is cut by a series of active northeast-striking
dip-slip faults resulting in horst and graben topography that exposes Miocene
sediments and Plio-Pleistocene lahar deposits within isolated topographic highs [3436]. These faults show up to 50 m of vertical displacement within a welded tuff dated
at 350 ka. Earthquake focal mechanisms, historical ground ruptures, mapped
Quaternary offsets, and mesoscale fault data from the Orotina debris fan are all
consistent with transtensional deformation across the northeast-striking marginperpendicular faults.
Up to five late Quaternary alluvial fill terraces (10-260 m elevation) occur along
the lower reaches of the fault-controlled Barranca and Tárcoles rivers [35]. Vertical
offsets of terrace treads and Holocene marine benches at the coast indicate active slip
along these faults. The upper river terrace (El Diablo surface) forms an extensive
upland along the foot of the Aguacate Cordillera [30, 35, 36, 219]. This surface caps a
thick accumulation (>50 m) of highly weathered alluvial gravel that exhibits a
distinctive, bright-red, clay-rich soil. This deeply weathered fill terrace resembles
others found along many of the major river systems draining the Chorotega forearc.
These pervasive valley-fill deposits are interpreted as uplifted alluvial prisms
formed during sea level rise toward eustatic highstands of the late Quaternary [35].
Lower, inset terraces may also reflect valley aggradation during periods of sea level
rise. A regional terrace correlation framework developed for the Costa Rican Pacific
margin [35] establishes constraints on the distribution and magnitude of fore arc uplift
during the Quaternary. These correlations are based on terrace elevations, radiometric
ages, soil and weathering rind characteristics, and stratigraphy of terrace deposits. The
total number of terraces, and the vertical spacing between them, varies along the coast
with respect to the magnitude of local tectonic uplift rates. This relationship suggests
that terrace generation along this coastline is strongly controlled by the interaction of
rock uplift and eustatic sea level fluctuation.
3.3.2.4 Herradura Headland
The Herradura headland (Fig. 3.7) exhibits the highest topographic relief within the
Chorotega fore arc (>1700 m). This fault-bounded block exposes late Cretaceous
oceanic basalts, which have been stripped of their sedimentary cover by rapid
Quaternary uplift and erosion. The differential uplift between the Herradura block and
adjacent lower-relief blocks is accommodated by dip slip along steep marginperpendicular faults [33-35]. Holocene river terraces and wavecut benches attest to
rapid uplift along the Herradura headland. The absence of Pleistocene terraces here
may reflect high uplift rates and accelerated erosion along the steep mountain front.
Rapid uplift of the Herradura block may be driven by seamount subduction beneath the
margin, as suggested by extensive scarring of the margin wedge offshore [151, 152].
3.3.2.5 Quepos-Parrita Coast
The Quepos-Parrita coastal piedmont (Fig. 3.7) southeast of the Herradura promontory
consists of a low-relief embayment in the coastal mountain front where the Fila
Costeña thrust belt merges with the northern Talamanca Cordillera. This area
encompasses the Esterillos, Parrita, and Quepos coastal fault blocks inboard of the
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32 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
rough domain on the subducting Cocos plate [33-35]. Several major rivers descending
from the interior highlands traverse the Quepos-Parrita piedmont on their way to the
Pacific coast. Active faulting in this area has disrupted drainage patterns, uplifting
Quaternary river deposits to form flights of fluvial terraces [220-225]. High sediment
loads have formed a low-relief coastline with barrier beaches and mangrove estuaries,
interrupted only by an isolated rocky headland at Quepos.
The rugged, high topography of the Herradura block (Fig. 3.7) descends abruptly
to the southeast where a major dip-slip fault separates it from the lower-relief upland of
the Esterillos block [33-35]. The dissected upland surface of the Esterillos block is
formed on a thick accumulation of alluvial gravels deposited by the paleo-Parrita river
[35, 225]. Four separate late Pleistocene terrace treads occur on these deposits, ranging
from 40-185 m in elevation above river level. These terraces extend up to 15 km
northwest of the Parrita river, indicating channel migration in response to late
Quaternary uplift and tilting of the Esterillos block. Like other fore-arc rivers along the
central Costa Rican coast, the Parrita river flows along a steep dip-slip fault oriented
perpendicular to the margin [33-35]. This structure accommodates differential uplift
between the Esterillos fault block and the lower-elevation Parrita block to the
southeast.
The smaller Quepos fault block (Fig. 3.7) has experienced pronounced uplift
relative to the surrounding Parrita lowlands. Similar to other peninsulas and
promontories along the Chorotega fore arc of Costa Rica and Panama, the Quepos
headland exposes Cretaceous-Paleogene oceanic basement rocks [33]. Several drainage
networks on the Parrita coastal plain are deflected around the Quepos highland and
exhibit at least four late Quaternary terraces that attest to active uplift [220-223].
3.3.2.6 Fila Costeña
The Fila Costeña (Fig. 3.7) is a steep-fronted, linear mountain range that runs subparallel to Costa Rica's southern coastline from the Herradura headland to the Panama
border [37, 220-224]. This abrupt coastal topography (>1 km of local relief) formed
during the late Cenozoic by rapid fore-arc shortening and crustal thickening inboard of
the subducting Cocos Ridge [37]. Four major thrust faults imbricate Tertiary rocks of
the Terraba basin, producing rapid uplift along the Fila Costeña range front. These
faults are exposed along the Terraba river gorge (Fig. 3.7), which cuts across the range
front, linking the General and Coto Brus valleys with the Pacific coast [32, 37, 224].
The Terraba river serves as the primary drainage for the Pacific slope of the Talamanca
Cordillera (Fig. 3.7) which rises to the northeast of the Fila Costeña. Four Quaternary
fluvial terraces occur along the Terraba gorge, with some surface elevations reaching
>250 m above modern river level [224]. Irregular terrace profiles, offset gravel
deposits, and sharp variations in mountain-front morphometry attest to active uplift and
faulting within the Fila Costeña thrust belt [220, 221, 224]. The frontal thrust of the
Fila Costeña separates a subsiding outer fore arc offshore of southern Costa Rica from
the onland area of rapid uplift within the inner forearc [37]. This pattern is broken only
directly inboard of the axis of the subducting Cocos Ridge, where rapid uplift in the
outer forearc has formed the Osa peninsula [29].
3.3.2.7 General and Coto Brus Valleys
The General and Coto Brus valleys (Fig. 3.7) occupy an elongate structural basin that
stretches for over 100 km along the Pacific slope of the Talamanca Cordillera. This
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
basin is separated from the Pacific coastal plain to the southwest by the Térraba thrust
belt within the Fila Costeña. A series of broad alluvial fans coalesce along the foot of
the Talamanca Cordillera, forming an extensive piedmont surface covering over 400
km2 of the valley bottom [226-229].
Tributaries of the General and Coto Brus rivers, which drain the Talamanca
highlands (Fig. 3.7), have deeply incised within this fan complex leaving a sequence of
terrace remnants along canyon margins. These alluvial surfaces are distinguished from
one another based on geomorphic setting, sedimentary texture, and the morphologic
and chemical characteristics of soils [226, 228]. The oldest geomorphic surfaces
coincide with the extensive piedmont upland in the northwestern portion of the General
Valley. These well-drained upland surfaces exhibit dark-red, deeply weathered lateritic
oxisols. A series of lower fan surfaces with less-developed soils yield late Pleistocene
radiocarbon ages. The youngest alluvial surfaces consist of low elevation aggradational
terraces inset along river canyons and abandoned braided channel bars of the General
and Coto Brus rivers.
3.3.2.8 Osa Peninsula
The Osa peninsula (Fig. 3.7) within the outer Chorotega fore arc of southern Costa
Rica has formed by rapid uplift and crustal shortening directly above the axis of the
subducting Cocos Ridge [29]. This rugged peninsula covers over 1200 km2 and
exposes a highly deformed sequence of late Cretaceous-Paleogene oceanic basement
rocks and acrreted marine sediments [204, 205]. The Osa peninsula segment of the
Middle America Trench is a known source for large (M ≥ 7.0) subduction earthquakes
associated with underthrusting of the buoyant Cocos Rdige [191, 192].
Quaternary marine sands, beach ridges, and alluvial gravels along the Osa
peninsula's shorelines record high rates of tectonic uplift (6.5-2.1 m/k.y.) that descrease
along an arcward trend from the peninsula's interior, northeastward toward the Dulce
Gulf [29, 224, 230]. Along the peninsula's abrupt seaward-facing coast, late Pleistocene
shallow marine sands dated at 27-50 ka are preserved in fill wedges overlying
basement rocks at >75 m above sea level [230]. Along the northeastern coastal
piedmont, a sequence of uplifted beach ridges yield radiocarbon ages ranging from <1
ka near the modern shoreline to >30 ka at an elevation of 25 m [29]. Rivers draining
the coastal piedmont exhibit two extensive Pleistocene gravel terraces that form a thick
alluvial apron across the fault-bounded mountain front [224]. These deposits overlie
nearshore marine sediments dated at >30 ka. Two lower terraces with late Holocene
radiocarbon ages occur adjacent to active channels attesting to continued uplift.
3.3.2.9 Burica Peninsula
The elongate Burica peninsula (Fig. 3.7) juts southward into the Pacific Ocean forming
a 25-km-long promontory at the Costa Rica-Panama border. This emergent fragment of
the outer Chorotega fore-arc exposes a basement of Cretaceous-Paleogene oceanic
basalts overlain unconformably by a Plio-Pleistocene sequence of marine sands,
conglomerates, and turbidite beds [28, 231]. Facies relationships and faunal
assemblages indicate that Pliocence subsidence was interrupted by rapid Pleistocene
uplift [28]. The Pio-Pleistocene sediments exhibit significant folding and vertical
displacement along a prominent north-trending fault valley that bisects the peninsula.
Uplifted wavecut platforms along the peninsula’s coast attest to ongoing deformation.
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34 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
Faulting and uplift here are attributed to subduction of the Cocos Ridge and passage of
the Panama Triple Junction [28].
3.3.2.10 Soná and Azuero Peninsulas
The Soná and Azuero peninsulas (Fig. 3.8) of western Panama together form a major
forearc promontory (>10,000 km2) that extends over 100 km southward into the Pacific
Ocean from the Panamanian isthmus. This prominent coastal landmass forms the
eastern edge of the Gulf of Chiriquí and the western shore of the Gulf of Panama (Fig.
3.8). Both peninsulas feature central mountain ranges (>500 m elevation) that are
separated from the volcanic cordillera to the north by east-west trending lowlands. The
two peninsulas are separated from each other by the narrow north-trending Gulf of
Montijo (Fig. 3.8). Offshore to the southwest of the Soná peninsula, lies Coiba Island
within the Gulf of Chiriquí.
The mountains of the Soná and Azuero peninsulas are both cut by the northwesttrending Soná-Azuero fault [38]. This major left-lateral strike-slip fault forms a
prominent lineament that cuts across the peninsulas along a series of aligned river
valleys. Deformation along the Soná-Azuero fault affects a 40-km-wide zone marked
by steep fault scarps and prominent linear valleys [38]. This fault separates two distinct
suites of basement rocks common to both peninsulas. South of the fault, the basement
is comprised of homogenous Cretaceous seafloor basalts, while to the north it consists
of a heterogeneous late Cretaceous-Eocene volcanic arc complex of basalts and
intrusive rocks overlain by intermediate lavas. Offshore to the southwest, the Coiba
fault zone runs parallel to the Soná-Azuero fault, resulting in uplift at Coiba Island
[232].
3.3.3 Chorotega Back Arc Province
The Chorotega Back Arc Province (Fig. 3.4) extends from the vast Caribbean plains of
the Tortuguero lowlands in northeastern Costa Rica (Fig. 3.7) to the abrupt emergent
shorelines of the southern Limón and Bocas del Toro basins near the Costa RicaPanama border. While the Tortuguero lowlands in the north feature an extensive lowrelief alluvial plain with a relatively monotonous shoreline, the southern Limón and
Bocas del Toro region exhibits a narrow, higher-relief coastal plain with a rugged
shoreline of rocky headlands and intervening embayments [171, 172]. The sharp
geomorphic contrast between these regions reflects a sudden shift along the Chorotega
back arc from relatively stable tectonics in the north, to active crustal deformation
within the North Panama deformed belt in the south.
3.3.3.1 Tortuguero Lowlands
The Tortuguero lowlands (Fig. 3.7) of the northern Chorotega back arc encompass an
extensive alluvial plain that reaches 40-70 km seaward from the base of Costa Rica's
Central volcanic cordillera. A series of major rivers draining the volcanic cordillera
traverse the alluvial lowlands, transporting a high sediment load for deposition across
broad inland flood plains and a coalescing delta complex at the coast. A sequence of
massive alluvial fans has developed along the foot of the volcanic cordillera where the
major rivers exit the mountain front [229]. In many cases, modern rivers have incised
below extensive upland fan surfaces comprised of thick accumulations of Pleistocene
fluvial gravels, capped by well-developed, deep-red, clay-rich soils [233]. These soils
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
and associated aggradational surfaces may be age correlative with the Pleistocene
alluvial terraces observed along Costa Rica's Pacific fore arc [35].
Along the Tortuguero coast (Fig. 3.7), the low-relief, sediment-laden shoreline
traces a broad, continuous arc for over 120 km between the San Juan River in the north
and the Limón headland in the south. This coastline consists of a 10-15 km wide band
of prograding, shore-parallel, beach ridges that stretch along the margin of the vast
alluvial plain. The lower reaches of rivers approaching the coastline are often deflected
between the shore-parallel beach ridges, resulting in a coastal morphology of elongate
lagoons and narrow barrier islands. At several locations along the Tortuguero coast, the
low-relief landscape is interrupted by abrupt hills generated by Neogene-Quaternary
back-arc volcanism. These volcanic hills, however, represent only a minor departure
from the overall monotonous topography of the Tortuguero lowlands.
3.3.3.2 Southern Limón and Bocas del Toro Coast
The low-relief landscape of the Tortuguero region contrasts sharply with the rugged
emergent morphology of the southern Limón and Bocas del Toro coastlines to the
south (Fig. 3.7). Along this southern segment of the Chorotega back arc, a narrow
coastal plain (<20 km) with undulating topography runs along the steep Caribbean
slope of the Talamanca mountains. This stretch of rugged coastline extends for >200
km from Costa Rica's Limón headland in the northwest (Fig. 3.7), to Panama's Bocas
del Toro archipelago and Gulf of Mosquitoes in the southeast (Fig. 3.8).
The coastal morphology of the southern Limón region is characterized by a series
of rocky promontories and coastal islands interspersed with pocket bays and wide
crescent-shaped beaches. Coral reefs and prominent cliffs occur along some segments
of coastline, while other areas feature broad estuaries, peat swamps, and barrier
beaches. At Bocas del Toro in northwestern Panama, an extensive low-relief coastal
embayment (70 km wide) lies inboard of an emergent string of cliff-lined islands and
promontories. To the east of Bocas del Toro, the Chorotega back arc extends along the
Gulf of Mosquitoes where a series of river deltas form localized bulges in the coastline.
The rugged geomorphology of the Limón and Bocas del Toro region (Fig. 3.7) is
controlled by active crustal shortening within the North Panama deformed belt along
the Caribbean margin of the Panama block [234]. Rapid uplift above northeast-verging
thrust faults has led to the emergence of Quaternary coral terraces along the southern
Limón coastline [235]. Active subsidence has also produced a low-relief trough
inboard of the emergent islands of the Bocas del Toro archipelago. During the 1991
M7.6 Valle de la Estrella earthquake, coseismic uplift of 0.5-1.5 m affected the
southern Limón coast [236], while subsidence of 0.5-0.7 m resulted in inundation of
peat swamps along the Bocas del Toro embayment [237]. Toward the northwest, the
zone of active coastal deformation ends abruptly at the Limón headland, where thrust
faulting within the North Panama deformed belt gives way to oblique slip along
steeply-dipping faults of the Central Costa Rica deformed belt [34, 235].
Uplift along the Limón-Bocas del Toro coast (Fig. 3.7) has exposed a Neogene
sequence of marine to terrestrial sediments and volcanic rocks along coastal cliffs and
islands [238-241]. These deposits are correlative with similar units mapped in the
Canal Zone and Darién regions of Panama [242, 243]. As a whole, this rock sequence
provides a detailed record of Neogene emergence along the Panama isthmus, resulting
in closure of the oceanic strait between the Atlantic and Pacific Ocean basins [8, 9].
35
36 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
Figure 3.8. Map of the physiographic provinces of southern Central America, showing
significant geomorphic features of portions of Panama and Colombia. Digital elevation
model derived from NASA Shuttle Radar Topography Mission (SRTM) image PIA03364.
3.3.4 Canal Zone Lowlands Province
The Panama Canal Zone (Fig. 3.4) occupies a region of relatively low topography
between the Central Volcanic Cordillera of western Panama and the mountainous
Darien isthmus to the east (Fig. 3.8). This lowland encompasses a network of lowgradient river valleys that drain surrounding hills with peak elevations of less than
1200 m [244]. The Pacific-Caribbean drainage divide descends to one of its lowest
elevations in Central America (<200 m) in the low saddle of the Culebra Cut along the
Panama Canal (Fig. 3.8). The most pronounced expression of low topography in this
region is the once-extensive swamp within the broad valley of the Chagres river, now
covered by the Panama Canal’s Gatún lake [245].
The stratigraphy of the Canal Zone Lowlands includes a Cretaceous volcanic
basement that is overlain unconformably by a thick sequence of Eocene-Miocene
shallow marine and terrestrial sediments [242, 244-248]. These rocks are moderately
folded, and were affected by late Neogene faulting and uplift that produced localized
bedrock highs within fault-bounded blocks [38, 245]. Within adjacent topographic
lows, these sedimentary rocks are buried unconformably by a horizontal valley-fill
sequence of Pleistocene-Holocene estuarine and swamp deposits referred to as the
Atlantic Muck.
3.3.4.1 Gatún Fracture Zone
The low topography of the Canal Zone (Fig. 3.8) has been attributed to pervasive
faulting and fracturing that extends across the Panamanian isthmus within an 80-kmwide zone referred to as the Canal Discontinuity or the Gatún Fracture Zone [244, 245,
248]. This major crustal discontinuity has been interpreted as a Neogene-age basement
fault that divides the Chorotega block to the west from the Chocó block of eastern
Panama and western South America [4].
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
Seismic imaging along the Caribbean coast indicates that faulting in the Canal
Zone post-dates late Miocene strata and may in some cases displace overlying
Quaternary beds of the Atlantic Muck [245]. Prominent geomorphic lineaments,
topographic breaks, and bends in river courses are all consistent with a young, faultcontrolled landscape [244-246]. For example, a major northeast-trending fault
lineament along the Río Gatún (Fig. 3.8) forms the southern boundary of a basement
highland at the northern end of the Canal Zone. This lineament extends eastward into
the northern coastal ranges of the Darién Isthmus and is interpreted as a major leftlateral strike-slip fault [38]. Abundant north-striking and generally east-facing scarps
south of the Gatún fault suggest that the Canal Zone is undergoing active east-west
extension across a series of normal faults [38]. These normal faults may represent the
western termination of left-lateral shearing along major strike-slip faults within the
Darién region of eastern Panama.
3.3.5 Darién Isthmus Province
The Darién Isthmus (Fig. 3.4) of eastern Panama is bounded by a northwest-trending
set of rugged mountains along both its Caribbean and Pacific coasts (Fig. 3.8). These
include the San Blas and Darién ranges along the Caribbean coast, and the Majé,
Bagre, and Sapo ranges along the Pacific side. These coastal highlands flank an
elongate lowland basin centered along the broad valleys of the Bayano, Chucunaque,
and Tuira rivers (Fig. 3.8). On the Pacific coast, the Gulf of San Miguel (Fig. 3.8)
forms a deep bight into the coastal mountains where the Tuira river estuary drains from
the central lowland into the ocean. Much of the humid and rugged landscape of the
Darién Isthmus remains cloaked in dense tropical vegetation, contributing to its
reputation as one of Central America’s most remote regions.
The coastal massifs of the Darién Isthmus expose a Cretaceous-Eocene crystalline
basement complex comprised predominantly of highly deformed mafic igneous rocks
[142, 243, 248, 249]. These rocks belong to the Chocó block (Fig. 3.1), an allocthonous
oceanic basement terrane that lies beneath eastern Panama and western Colombia [4].
The Chocó block is separated from the Chorotega block to the west, across Tertiary
basement faults of the Panama Canal Discontinuity.
The basement rocks of the Darién region are overlain along the flanks of the
coastal mountains by Eocene-Miocene pillow basalts and deep marine sediments
deposited prior to Panama’s collision with South America [243]. These rocks are inturn buried by a thick, post-collisional sequence of Neogene siliciclastic sediments
within the core of a complex synclinorium centered along the Bayano-Chucunaque
basin.
Within Panama and southern Costa Rica, the Chocó and Chorotega basement
terranes (Fig. 3.1) together form the modern Panama block, a semi-rigid microplate
that is caught between the Caribbean, Cocos, Nazca, and South American plates [5, 6].
Fold and thrust belts offshore of both the northern and southern Darién isthmus (North
and South Panama deformed belts) accommodate active convergence with the
Caribbean and Nazca plates [39]. Active collision between the Panama block and the
South American craton to the east occurs across thrust faults of the Atrato-Urubá suture
zone in western Colombia [148].
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38 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
3.3.5.1 East Panama deformed belt
Ongoing collision between the Panama block and South America results in clockwise
rotation and left-lateral slip along several major northwest-trending faults that cut the
eastern Darién Isthmus [38]. Together, these structures constitute a diffuse deformation
zone referred to as the East Panama deformed belt [42]. The Sansón Hills, Sambú,
Majé, and Jaqué River faults (Fig. 3.8) each follow prominent northwest-trending
lineaments along the flanks of the Pacific coastal ranges.
The Sansón Hills fault forms the boundary between the Chucunaque basin (Fig.
3.8) and the coastal highlands to the southwest [38, 42]. Hilly topography northeast of
the fault exposes Paleogene sediments of the Chucunaque basin within a series of
breached, en-echelon anticlines. These folded strata are juxtaposed against Cretaceous
oceanic basement rocks exposed southwest of the fault within the estuarine lowlands of
the Tuira river.
The Sambú fault, southwest of the Tuira river (Fig. 3.8), marks the boundary
between the Bagre and Sapo massifs near the coast [38, 42, 250]. A left-step in this
fault bounds the Sambú pull-apart basin, which forms the entrance to the Gulf of San
Miguel and a broad alluvial valley between the Bagre and Sapo ranges (Fig. 3.8). The
Majé fault trends onshore to the northwest from the Gulf of San Miguel where it offsets
basement rocks of the Majé massif [38, 42]. The Jaque River fault along the southwest
range front of the Sapo Massif follows the Pacific coast southeastward from the Darién
isthmus into western Colombia [38, 42, 250].
The northwest-trending left-lateral faults of the Darién Isthmus terminate at their
southeastern ends along a zone of north-trending thrust faults within the Panama-South
America suture zone [38, 42, 243]. Toward the northwest, the left-lateral faults die out
as they approach north-trending extensional structures along the Canal Zone
Discontinuity. The presence of undeformed Pliocene-Pleistocene sediments along fault
valleys in the eastern Darién Isthmus may indicate that the left-lateral faults are no
longer active [243]. If this is the case, the Panama block in this region may now be
acting as a rigid plate as it collides with South America.
3.4
SUMMARY
The geomorphology of Central America is extraordinarily rich and varied (Fig. 3.4).
This small fragment of land linking North and South America features a diversity of
landforms and geomorphic processes usually associated with an entire continent. While
accounting for only 0.4 % of the Earth's total land area, Central America encompasses
a wide range of landscapes, from jungle-covered tropical lowlands to glaciated
highland plateaus, from cloud-forested volcanic peaks to rolling dryland savannahs,
and from rocky tectonic shorelines to low-relief barrier islands and mangrove estuaries.
This chapter presents a broad overview of Central American geomorphology, and
defines a system of physiographic provinces (Fig. 3.4) that serves as a framework for
characterizing regional landscapes and geomorphic processes.
The physiographic trend of the Central American isthmus is defined by the Middle
America trench and volcanic front (Fig. 3.1), active since the initiation of subduction in
the late Cretaceous. Cenozoic magmatic rocks and adjacent sedimentary basins are
overprinted across four crystalline basement terranes, two of continental affinity
beneath northern Central America (Maya and Chortis blocks), and two of oceanic
origin (Chortis and Chocó blocks) beneath the southern isthmus. This geologic
CENTRAL AMERICA: GEOLOGY, RESOURCES AND HAZARDS; BUNDSCHUH & ALVARADO (EDS)
template (Fig. 3.2) is in turn affected by active tectonics within three major plateboundary deformation zones: the Motagua-Polochic transform faults of Guatemala, the
Middle America convergent margin along the Pacific coast, and the diffuse collisional
belts along the margins of Panama and Costa Rica. The delicate interplay between
Central America’s highly variable climate and topography (Fig. 3.3) imparts an
additional influence over regional geomorphology.
The Maya Highlands Province (Fig. 3.4) of northern Central America includes a
series of high-altitude mountain ranges and plateaus that extend in a broad arc from
Central Mexico, across northern Guatemala, to Belize. These highlands descend to the
north onto the vast carbonate lowlands of the Yucatán Platform Province (Fig. 3.4), the
most extensive karstlands of the North American continent. Along the southern margin
of the Maya highlands, the Motagua Fault Zone Province (Fig. 3.4) extends across
central Guatemala along a series of major fault-controlled valleys that define the active
North American-Caribbean plate boundary.
The Chortis Volcanic Front Province (Fig. 3.4) parallels the Pacific margin from
Guatemala to El Salvador, and consists of a series of clustered stratovolcanoes and
calderas arranged along transverse fault lineaments. Along the Pacific slope, the
Chortis Forearc Province (Fig. 3.4) encompasses a broad coastal plain made-up of
coalescing alluvial debris fans that descend from the volcanic highlands. Behind the
volcanic front, and south of the Motagua fault zone, the Chortis Highlands Province
(Fig. 3.4) extends across the mountainous interior of Guatemala, Honduras, and
Nicaragua. This extensive region of high topography includes a rifted plateau in the
west, a stable central massif, a northern coastal borderland of fault-bounded ridges, and
an eastern zone of dissected mountains facing the Caribbean coast. The Mosquito
Coast Lowlands Province (Fig. 3.4), east of the Chortis highlands, encompasses the
extenisve alluvial plains along the Caribbean coast of Honduras and Nicaragua.
The Nicaraguan Depression Province (Fig. 3.4) consists of a fault-bounded
structural basin that extends for 600 km between the coastal fore arc and the Chortis
highlands. This tectonic lowland includes the Median Trough of El Salvador, the Gulf
of Fonseca, and Lakes Managua and Nicaragua. The Nicaraguan Volcanic Front
Province (Fig. 3.4) encompasses a chain of stratovolcanoes and calderas centered along
the southwestern boundary faults of the Nicaraguan depression. The Sandino Fore Arc
Province (Fig. 3.4), southwest of the Nicaraguan volcanic front, includes a low relief
coastal plain composed of volcaniclastic debris in the north, and a rugged shoreline of
pocket bays and rocky headlands in the south.
The Chorotega Volcanic Front Province (Fig. 3.4) of Costa Rica and Panama
consists of a segmented series of distinct cordilleras that have evolved in response to
highly variable tectonics along the southern Middle America margin. A major volcanic
gap occurs along an uplifted segment above the subducted Cocos Ridge. The adjacent
Chorotega Fore Arc Province (Fig. 3.4) encompasses a rugged tectonic coastline,
characterized by prominent uplifted headlands and peninsulas, as well as an active fold
and thrust belt inboard of the Cocos Ridge. The Chorotega Back Arc Province (Fig.
3.4) features a broad alluvial lowland in northern Costa Rica and a rugged coastline
with uplifted coral reefs formed within an active back arc thrust belt. The Canal Zone
Lowlands Province (Fig. 3.4) includes a swath of densely fractured, low relief
landscape that extends across central Panama. To the east, adjacent to South America,
the Darién Isthmus Province (Fig. 3.4) consists of a fault-bounded series of humid
coastal mountain ranges flanking an elongate central valley.
39
40 THE GEOMORPHOLOGY AND PHYSIOGRAPHIC PROVINCES OF CENTRAL AMERICA
As described throughout this chapter, the physiographic provinces of Central
America (Fig. 3.4) each exhibit a characteristic assemblage of landforms that records a
unique history of landscape evolution. The distinctive geomorphology of each province
reflects a dynamic interplay between regionally variable rock types, active plateboundary tectonics, and an energetic tropical climate. As a whole, the physiographic
provinces of this dynamic region encompass an exceptionally diverse array of
landscapes and associated landforms. Central America, therefore, serves as an
outstanding geomorphic laboratory for the study of a broad range of surface processes
and their imprint on the landscape.
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