ABSTRACT: Glacial geomorphologists study the impacts of glaciers on
landforms; glaciologists study the distribution and behavior of snow and ice on
the earth’s surface; glacial geologists study the geologic materials delivered by
glaciers. Glacial geomorphology is a combination of landform studies and process
studies. Since the mid-19th century, the science has engaged in considerable
debate – around processes, erosion capability, and relative to the shaping of
Yosemite Valley, glaciers versus faulting. Glacial erosion occurs through
mechanical processes of abrasion, quarrying, and subglacial meltwater. A suite of
landforms including striae, roches moutonnées, cirques, and channels are the
result of glacial erosion. The Sierra Nevada range, and particularly Yosemite
National Park, provides aesthetically striking examples of these landforms. In
addition to overviews of glacial geomorphology research to date, and glaciations
that have affected Sierra Nevada, this paper will address processes that shape the
landforms we now see. It will conclude with the direction in which glacial
geomorphology is headed in the 21st century.
INTRODUCTION
Glacial geomorphology is a combination of landform studies and process studies. Though until
the mid-20th century, process-oriented approaches to explain landform development were largely
discarded in favor of mainstream geomorphology of 19th and early 20th centuries which stressed
deductive models of landform change over long time spans (i.e., W.M. Davis’ Geographical
Cycle) (Harbor 1989). In 1840, after touring the glaciers in the Chamonix district of the Alps,
Louis Agassiz, a Swiss-American, Harvard-educated natural scientist, published his theory of
continental glaciation, whereby glaciers once extended beyond their present boundaries. Based
on his observation of glacial striae and other landform features down valley of existing glaciers,
he proposed that vast sheets of ice had once covered much of the northern hemisphere; avantgarde thinking for the time period considering the ice sheets of Greenland and Antarctica were
undiscovered. After initial opposition the concept of continental glaciation took hold and was
widely accepted among glacial geologists and glaciologists for decades to follow. By the mid1800’s, there were three accepted components of glacial theory (Aber 2003):
 Alpine glaciers had once extended farther down valley than present boundaries
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 Mountain ice caps formed from much thicker ice or in higher mountains and spread into
adjacent regions
 Continental ice sheet spread from the Arctic and covered all of Europe as far south as the
Mediterranean
Additionally at this time, studies on glacier movement and glacial erosion were emerging.
Research on glacier movement in the Alps was being conducted by Agassiz and James D.
Forbes, a Scotch physicist. From this emerged the theory of viscous (plastic) deformation, which
added to the then-current theories of regelation and dilatation (Aber 2003). The basic processes
of glacial erosion were being outlined by an Irishman, John Tyndall. He identified two agents at
work in the case of every glacier – ice and water. The former uses its weight to comminute or
tear rock from its bed while the latter accumulates on the bed of the glacier and washes the
detritus away (Harbor 1989). Although the significance of glacial erosion in the development of
major landforms was debated, by the early 20th century it was generally accepted that glaciers
were capable of significant erosion (Harbor 1993). Subsequently, with glacial theory firmly
established, glacial geomorphology turned its focus to describing conditions in areas with
existing glaciers and interpreting landforms in areas of previous glacier activity. Davis’ youthmaturity-old age theory still dominated glacial geomorphology but in the mid-20th century
studies began to emphasize landform and stratigraphy to reconstruct glacial history. Further,
geomorphic research techniques shifted towards process measurements and numerical
descriptions of form (Harbor 1993). Physics-based glaciology contributed to the understanding
and modeling of ice flow and glacial hydrology, however, application of these advances to
understanding the links between flow, erosion and deposition were few. Glacial geomorphic
research in the 1970’s and 1980’s focused on two areas: operation of processes through
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instrumentation and theoretical analyses based in glaciology, mechanics, chemistry, and
sedimentology; and using knowledge of processes at small scales to examine larger-scale
problems of landform development (Harbor 1993). Most recently, studies are of global
environmental focus: examining environmental imprints recorded in marine- and ice-cores; and
testing models of environmental change and ice sheet behavior (Glasser and Bennett 2004). To
date, depositional landforms, which are more easily dated than erosional landforms, have served
to answer questions in these areas. Consequently, depositional landforms are more widely
understood than glacial erosional landforms. Nonetheless, glacial erosional processes and
landforms play important roles in glacial geomorphology. Glasser and Bennett (2004) propose
three reasons for their importance.
 Subglacial erosion provides the sediment that underlies many of the Earth’s large ice
masses; glacial erosion determines the subglacial deforming layers and their associated
landforms and sediments
 Glacial erosion helps determine sediment yields in fluvial and fjordal settings, in longterm landscape evolution, and in relief production
 Landforms of glacial erosion are used as palaeo-environmental indicators. They shed
light on former glacial climates, in a geological-time context
The aim of this paper is to discuss glacial erosional processes and resulting landforms. A
particular focus will be given to the Sierra Nevada area within California. The above
introduction on glacial geomorphology research from mid-19th century to date provides
background on the evolution of studying the science. An overview of glaciations that affected
North America, and Sierra Nevada especially, will condition the reader to better understand the
focus of the paper: the processes that shape the landforms we now see. A closing section on
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recent techniques and models related to erosional processes will inform as to the direction in
which glacial erosional studies are headed within glacial geomorphology.
GLACIATIONS
By the end of the 19th century, after glacial theory had taken hold, the concept of multiple
glaciations separated by interglacial episodes was introduced. Polished rock outcrops, rounded
hills covered with debris, and valleys filled with sand and gravel deposits were evidence. In
Europe and North America, four glacial periods were identified as occurring during the
Pleistocene epoch which began ~1.8 million years ago. Ice sheets covered all of Canada and
large portions of the northeast and north-central United States. Glacial periods are time spans
when glaciers advanced and retreated. Interglacial episodes are periods of warmer temperatures
when glaciers retreated. We’re currently experiencing an interglacial episode. The concept of
glacial advance and retreat involves accumulation and ablation. When snowfall accumulation
(and subsequent compaction into ice) is greater than ablation (melting, evaporation) the weight
of the ice causes the mass to flow. This is known as glacial advance. Glacial retreat occurs when
ablation is greater than accumulation. The toe of the glacier is farther up valley than during a
glacial advance. The literature varies in regard to the actual number of glacial periods and the
dates around the Pleistocene epoch, but for the purpose of this general overview, focus will be
given to the identified four in the following widely accepted timeframes. These glacial periods
are, from oldest to most recent (Stoffer 2003):
 Nebraskan – oldest (began ~2 million bp and ended ~1.65 million bp)
o Aftonian interglaciation (period between 900,000 bp – 1.65 million bp)
 Kansan (began ~900,000 bp and ended ~750,000 bp)
o Yarmouth interglaciation (period between 400,000 bp – 750,000)
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 Illinoian (began ~400,000 bp and ended ~250,000 bp)
o Sangamon interglaciation (period between 80,000 bp – 250,000 bp)
 Wisconsin – most recent (began ~80,000 bp and ended ~10,000 bp)
The glaciations are named after the states where till (unsorted mixtures of clay, sand, gravel, and
boulders) was extensively deposited and essentially covered the landscape. The unconsolidated
covering is known as ground moraine. Relative to the western United States with the exception
of northern Washington, glaciers in southern Washington, Oregon and California were
independent of the ice sheets that covered Canada and northern regions of the United States
(Guyton 1998). The glaciers of these regions formed in various mountain ranges and never
completely covered the landscape as is typical with ice sheets. Eliot Blackwelder was the
esteemed Stanford geologist whose field work in the early 1930’s on the eastern slope of the
Sierra Nevada produced evidence of four major glaciations that affected the area. These were the
McGee, Sherwin, Tahoe, and Tioga, for the most part named after locations where deposits were
found. Concurrent with Blackwelder’s field work, Francois Matthes, a respected geologist as
well, was studying glacial deposits on the west slope and named three glaciations: Wisconsin, El
Portal, and Glacier Point. Guyton (1998) notes that glacial record on the east side of the Sierra
Nevada is better preserved and easier to study than that on the west side. For example, lateral,
terminal, and recessional moraines in Lee Vining Canyon are visible east of Tioga Pass whereas
most of the terminal and recessional moraines on the west side have been removed by meltwater
streams. Therefore, Matthes glaciations have largely been put aside in favor of Blackwelder’s
four. However, Matthes’ Wisconsin glaciation includes aspects of the Tioga and Tahoe
glaciations; and his El Portal glaciation is probably the equivalent of the Sherwin (Huber 1989).
Other glaciations, such as the Hilgard, Tenaya, and Mono Basin, have been recognized but are
now regarded as part of the more important, longer-duration Tioga and Tahoe glaciations
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(Guyton 1998). The Sherwin glaciation covered more area than the Tahoe and Tioga, and
extended from Lassen region to as far south as Mt. Whitney area. It lasted ~300,000 years and
ended ~1 million years ago. Relative to Yosemite Valley, glaciers of Sherwin-age did the most
shaping by straightening and widening the Merced River canyon. This is a result of the flow
velocity of ice. The erosive force is concentrated on the insides of bends, as opposed to streams
which erode outsides of bends. The result is a wider, straighter valley. Descending from Sierra
ice fields, the glaciers extended westward up to 60 miles as far as the community of El Portal just
outside Yosemite National Park’s boundary. Beyond this, the canyon starts to meander and has a
V-shape as opposed to the more common U-shape of glaciated valleys. W.J. McGee’s glacial
erosion laws proposed in the late 19th century provide some explanation of the physics behind the
U-shape of glaciated valleys. He considered the distribution of ice velocity and weight across a
V-shaped valley occupied by ice. The effectiveness of glacier ice, he determined, increases from
center to sides. However, as Harbor (1989) points out from McGee’s explanation, he did not
identify whether maximum erosion occurs at the margin of the glacier or somewhere between the
center and the margin. Harbor concludes that maximum erosion must occur somewhere between
the center and the margin in order for the form to be concave-inwards (U-shape). Yosemite
Valley’s flat floor, rather than U-shape belies its glacial origin. Further explanation will be
provided in the section on the Tioga glaciation. Returning now to the Sherwin glaciation, during
this time ice filled the Merced River canyon nearly to the rim. The top portions of landmarks
such as Half Dome, El Capitan, Clouds Rest, Eagle Peak, and Sentinel Dome remained above the
ice. The glaciers excavated this central valley to a greater depth, due to the greater thickness of
the ice and erosive power, than smaller tributary valleys perpendicular to the main channel.
When the ice retreated, these tributary valleys were left ‘hanging’. Hence the term hanging
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valley, which was coined by pre-eminent geologist, G.K. Gilbert while inspecting Alaskan fjords
in 1899 (James 2003). Bridalveil Falls in Yosemite Valley is an example. James (2003) notes,
however, that hanging valleys are not exclusively the result of glacial activity. Hanging valleys
are common in the Sierra Nevada foothills below the glacial limit. Late Cenozoic uplift
steepened valleys which increased fluvial erosive power and incision rates of main channels.
This left tributary valleys hanging. The next significant glaciations in the Sierra Nevada were the
Tahoe and Tioga glaciations which ended ~75,000 and ~10,000 years ago, respectively. These
were smaller in areal extent and briefer than the Sherwin glaciation. Huber (1989) suggests that
the Tioga glaciation began ~30,000 – ~60,000 years ago and reached its maximum extent
~15,000 – ~20,000 years ago. Relative to Yosemite Valley, glaciers during the Tahoe and Tioga
advanced as far as El Capitan and Bridalveil vicinity, nearly ten miles east of El Portal. Ice
thickness was not much more than 2000’ at its maximum and did not fill the valley nearly to the
rim as it did during the Sherwin glaciation when thickness reached a maximum nearly twice that
(Huber 1989). When ice retreated it left a lake in the canyon and a terminal moraine that acted as
a dam from El Capitan to Bridalveil. As the separate arms of the Tioga glacier retreated up the
Merced and Tenaya canyons the meltwater delivered large quantities of sediment to the lake.
When the lake filled in with sediment it became today’s level valley floor. Josiah D. Whitney,
esteemed California geologist educated at Yale, and John Muir, the Sierra Nevada uber-naturalist
disputed the process which shaped the valley floor. Although Whitney acknowledged glacial
features, he thought Yosemite Valley was a graben formed by down dropping of rock between
faults. The flat floor of the valley led him to believe this. Muir on the other hand, was convinced
that glaciers carved Yosemite Valley and was happy to educate the public on his observations
and theories. His expertise in combining science and poetry elevated him to a beloved status
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among contemporaries (except Whitney) and the general public (Guyton 1998). Another
intriguing glacial phenomenon merits mention; and that is the difference between Yosemite
Valley and Hetch Hetchy Valley, 15 miles to the north. Both experienced the Tioga glaciation
yet the landscapes are different in some respects. Features such as Cathedral Spires, Sentinel
Dome (pinnacle), and the recessed waterfalls of Yosemite Valley are atypical of landscapes
carved, shaped, and smoothed by glaciers. Hetch Hetchy Valley on the other hand, has relatively
smooth walls and no pinnacles. Whereas Tioga glaciers did not fill Yosemite Valley nearly to the
extent that Sherwin glaciers did, they did fill Hetch Hetchy Valley. Therefore, features above the
level of Tioga ice in Yosemite Valley had one million years to weather, whereas Hetch Hetchy
Valley was filled to the rim with ice as recently as 10,000 years ago. One million years of
weathering produced the widened joints and fractured rock evident in Cathedral Spires, Sentinel
Dome, Leaning Tower, and Lost Arrow (Guyton 1998).
GLACIAL EROSIONAL PROCESSES
“Glacial erosion involves the removal and transport of bedrock and/or sediment by glacial
abrasion, glacial quarrying, and subglacial meltwater” (Glasser and Bennett 2004, 43). These
mechanical processes involve ice, water, embedded debris, gravity, and pressure. Continuing in
the Yosemite Valley theme, it is essential to note the geology and the occurrence of joints, and
the effectiveness of glaciers on these elements. Technically, Yosemite Valley contains more
granodiorite, diorite, and gabbro than commonly thought granite. Granodiorite is a crystalline
igneous rock that contains the minerals quartz, potassium feldspar, and plagioclase which is a
calcium-rich feldspar; for simplicity purposes, 25%, 25%, and 50%, respectively. Granite differs
from granodiorite in that it contains more quartz and potassium feldspar than plagioclase; again,
for simplicity, 37%, 37%, and 26%, respectively. Diorite and gabbro contain essentially no
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quartz or potassium feldspar. Unlike granite, granodiorite, diorite, and gabbro are more jointed,
weather more rapidly, and are therefore more easily eroded by glaciers (Guyton 1998). Tenaya
Canyon, just east of Yosemite Valley does not exhibit the wide, open flat-floor like Yosemite
Valley, and reflects a lesser degree of glacial erosion effectiveness due to its local rock.
Current literature reveals fewer studies of glacial erosional processes than glacial deposition
processes. Brocklehurst and Whipple (2002) note the lack of quantitative understanding around
mesoscale effects of glacial erosion, however they acknowledge mesoscale glacial erosion
modeling projects currently underway. In one of their studies, Brocklehurst and Whipple (2002)
investigate glacial erosion’s impact on the relief structure of the Sierra Nevada landscape. They
studied 28 drainage basins which experienced varying degrees of glaciation. All were located
between the towns of Big Pine and Lone Pine near Owens Valley. They found that glaciated
basins on the eastern side have ~80m greater average relief than nonglaciated basins, and
concluded that glacial erosion produces relief high in the drainage basin in the cirques and a
lesser degree of relief in areas where tributaries converge. In his 2003 article on glacial erosion
in northwest Sierra Nevada, L. Allan James notes the “dearth of glacial geomorphic knowledge”
(285) of this area through most of the 20th century. G.K. Gilbert studied micro- and meso-scale
glacial features and processes, in Yosemite Valley among other places, in the early 20th century.
However, as noted by Huber (1989), both his and W.J. McGee’s process-oriented approaches to
geomorphology were overshadowed by Davis’ evolutionary approach to understanding landform
development.
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In addition to glacial erosional macro-scale landforms (1km or greater in dimension) such as Ushaped valleys and hanging valleys discussed earlier, there are micro-scale landforms (below 1m
in size) such as striae, gouges, and p-forms; and meso-scale landforms (between 1m and 1km in
size) such as roches moutonnées. Other significant macro-scale features which will be addressed
include cirques, arêtes, and horns. This list represents a sampling of glacial erosional landforms
and is by no means complete. A thorough discussion of all glacial erosional landforms is beyond
the scope of this paper. Therefore, familiar landforms and the processes which shaped them have
been selected for discussion.
GLACIAL ABRASION
Glacial abrasion is the interaction between sediment in the basal layer of temperate glaciers and
the bedrock surface. Polish, striae, and gouges are the result of abrasion. Melting at the base of
the glacier leads to downward ice velocity that forces embedded debris within the base of the
glacier to scrape against the surface of the bedrock. Steep gradient, an abundance of basal
sediments, and melting at the base are key factors. Silts are the predominant sediment at work in
creating the smooth, almost glassy appearance of polish; while sand and gravel abrade to create
striae (Figures 1 and 2, respectively). It is interesting to note that polish and striae are more
evident on rock that resists weathering. The granodiorites of Yosemite Valley are prone to
exfoliation and disintegration and do not preserve surface features well. Therefore, polish and
striae are not as common in this area as they are in Tuolumne Meadows where plutonic rock is
more resistant (James 2003).
Striae, abrasions in rock formed by different ice flow directions, are significant to
reconstructions of former ice sheets because they provide evidence of the final orientation of the
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ice flow. Conditions for striation formation include basal debris, basal melting which causes
sliding, effective normal pressure, and transportation of debris. Glasser and Bennett (2004)
identify three morphological categories of striae based on depth, width, and contact geometry
between a fragment and bedrock beneath. They state that depth and continuity of a striation is a
balance between effective normal pressure which keeps debris at the base of the glacier in
contact with its bed, fluctuations in water pressure, and the plowing angle at which the abrading
fragments impact the bed. See figure 2 which illustrates different ice flow directions across the
rock.
Similar to striae, gouges can provide information regarding ice flow direction. Gilbert was one of
three people who identified three types of gouges: chattermarks, crescentic gouges, and
crescentic cracks (Glasser and Bennett 2004). Gouges form when rock, embedded in the base of
a glacier, exerts pressure at a point in the bedrock. The underlying rock is elastically deformed
until a threshold is exceeded and a sliver of rock is dislodged; except in the case of crescentic
cracks which fracture the rock without removal of fragments. Gilbert analyzed the result of
pressure when a boulder is pressed into bedrock due to the weight of ice. The bedrock’s elasticity
creates a ridge bowed up around the point of concentrated pressure. The moving ice continues to
push the boulder forward until the elastic limit of the bedrock is reached and fracturing occurs. A
wedge of bedrock is removed and leaves a gouge. The orientation of the ‘horns’ of chattermarks
and crescentic gouges, in combination with the direction of the forward dip of the fracture is an
indicator of ice movement direction. In crescentic gouges, the ‘horns’ are turned forward in the
direction of ice flow, in contrast to chattermarks in which the ‘horns’ are turned away from the
direction of flow. One could infer from this overall process that gouges are developed under
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thick ice. However, this conflicts with James’ (2003) observation of roches moutonnées, on
which polish, striae, and gouges can often be seen, in the South Yuba Canyon. We now turn to
roches moutonnées.
GLACIAL QUARRYING
Roches moutonnées are meso-scale, asymmetric landforms with gently inclined stoss sides and
steep lee sides. Sizes vary from a few meters to 150m in height (James 2003). They are shaped
through glacial erosional processes of abrasion and plucking. Lembert Dome (Figure 3) in the
Tuolumne Meadows area of Yosemite National Park is an example of a roche moutonnée. As the
glacier was moving across the landscape it encountered resistant rock. The ice pushing against
the rock created higher pressure in this initial area of contact known as the stoss side. Under
pressure, ice will melt at a lower temperature. This pressure-melting process is known as
regelation. The glacier then continued to move over and around the rock. As it moved, rock
fragments such as silt, sand, gravel, and boulders embedded in the base of the glacier abraded the
stoss side of the rock leaving a polished, striated appearance. The meltwater then infiltrated
crevices in the rock. Rock fracturing is the process which results in cracks and crevices which
then leads to plucking on the lee side of the rock. Sugden et al (1992) discuss three processes of
rock fracturing: frost shattering, wedging of rock fragments, and subglacial water pressure
variations. Frost shattering is a result of water entering existing rock fractures, re-freezing, and
expanding or shattering the rock. Wedging is self explanatory; and water pressure variations
involve water in a crack and an adjacent cavity. When the pressure in the cavity is reduced
suddenly and the high pressure remains within the surrounding rock, fracturing can occur. In his
field study in the early 1940’s, Carol (1947) descended by way of crevasses into the Grindelwald
glaciers in Switzerland. A subglacial cave system allowed him to examine conditions under
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which regelation occurs. He compared the movement of upper layers of ice to lower layers of ice
around a rock. The upper layers were moving at a rate of ~37cm per day whereas the lower
layers, due to increased pressure, had taken on a plastic, semi-viscous fluid state and were
moving at a rate of ~72cm per day. Returning now to the process of plucking, meltwater entered
crevices and refroze in the low pressure area (lee side) causing fracture and weakened rock. As
the glacier continued its forward movement into the low pressure area it plucked away chunks of
rock attached to the ice. L. Allan James (2003) observed a pair of roches moutonnées that
actually impeded the flow of the valley glacier at the bottom of the upper South Yuba Canyon.
The height of these hills is ~135m above the bench on which they rest, ~300m above the floor of
the canyon. Mapping of the Tioga maximum elevation nearby indicates that these roches
moutonnées were created under thin ice (<30m thick above the hilltops). I presume then, that the
elevated location of the roches moutonnées combined with the thinness of the ice caused a dam
of sorts that impeded the flow of the glacier. Additionally, it is easier for meltwater to infiltrate
lee-side cavities under thin ice. Cirques are erosional landforms developed through a positive
feedback process of freeze/thaw and glacial quarrying. Snow and ice accumulate at the head of a
glacier. When temperatures increase, ice plucks blocks of rock away from the head of the cirque
exposing new rock to freezing and thawing. A hollow depression begins to take shape. The
plucked blocks become embedded in the main glacier and are transported out of the cirque. This
continued process of erosion results in a cirque’s steep headwalls and sidewalls. Haynes (1998)
has suggested that cirques will evolve to an equilibrium planform, however, generally, the larger
a cirque, the greater the period of glacial erosion (Glasser and Bennett 2004). As a cirque’s
headwall and sidewalls are quarried by freeze/thaw action and thus enlarge the cirque both
backward and downward, the width of the ridges separating cirques decreases. A knife-edge
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ridge known as an arête develops between the cirques. Further to this picture, as cirques continue
to enlarge, the space separating the backwalls of three or more cirques decreases. Eventually, a
jagged peak known as a horn remains. Arêtes have evolved into steep ridges, sidewalls have
been reduced, and therefore, protection of snow and ice from summer sun is decreased, which in
turn reduces the rate of glacial erosion.
SUBGLACIAL MELTWATER
The effectiveness of meltwater as an agent of erosion depends on the resistance of the rock and
its structural weaknesses; the water velocity and the level of flow; and the quantity of sediment
in transport (Glasser and Bennett 2004). Figure 4 shows sediment-filled subglacial meltwater
emerging from a source at the snout of Aktineq Glacier in Nunavut, Canada. The term ‘p-form’
applies to a variety of landforms including sinuous depressions and grooves on glaciated
surfaces. Their forms were originally attributed to the plastic flow of ice around bedrock
surfaces; hence ‘p-form’. However, ‘s-form’ is also used since subglacial meltwater was the
agent (Glasser and Bennett 2004). Potholes and channels are common landforms shaped by
subglacial meltwater. James (2003) notes that temperate glaciers often have elaborate subglacial
drainage systems with hydraulic pressures that vary at different times. For example, pressure
may increase during spring melt season which may influence sliding velocity and erosion rates
which in turn influence landform development. Potholes may develop as a result of this process
when a rock lodges itself in the bedrock; the increase in meltwater increases the rate of erosion
which in turn causes a depression to develop beneath the rock. Another landform developing
from subglacial meltwater are channels which may cut across or be oriented transverse to surface
contours and present-day drainage patterns due to the hydraulic gradient within the glacier
(Glasser and Bennett 2004). The gradient is determined by glacier slope and topography beneath
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the glacier. The pattern embedded in rock at Olmsted Point (Figure 5) may have been eroded by
subglacial meltwater. Aspects of a subglacial drainage system such as areas of ice/bed contact,
ice/bed separation, and precipitate-filled depressions are essential in the reconstruction of former
drainage conditions. By reconstructing, estimates can be made of former ice surface slopes and
ice thickness (Glasser and Bennett 2004).
GLACIAL GEOMORPHOLOGY IN THE 21st CENTURY
As technology continues to improve and accelerates advances in science into the 21st century,
and increased attention is paid to the global environment, the role of glacial geomorphology will
thus increase. Recent techniques to more easily access present-day glacier beds include ice radar,
seismic profiling, and glacier borehole drilling. These techniques improve understanding of the
physics and mechanics of glaciers and resulting landforms (Glasser and Bennett 2004). In his
article on modeling processes and landforms, Harbor (1993) discusses glacial process-form
modeling into the 21st century. He identifies three key areas of increasing importance:
 Addressing the three-dimensional nature of flow and form development problems
 Dealing with issues surrounding the importance of glacial erosion because this leads to an
understanding of changing sediment production which is used to address past changes in
climate and tectonic activity
 Addressing the issue of rapidly deforming subglacial layers of sediment (zone of
interaction between glacier ice and underlying material)
The significance of glacial erosion in the development of landforms has been a subject of debate,
off and on, since the late 19th century; beginning with McGee’s glacial erosion laws proposed in
1894 – the first detailed, process-oriented explanations for some landforms – that were largely
discarded at the time, to present-day concerns over the difficulty of establishing past and present
rates of glacial and nonglacial processes (Harbor 1993). As past work is re-examined in the
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context of an evolving discipline, Harbor (1993, 132) pointedly remarks, “The application of
process studies to form development provides an opportunity to examine how spatial and
temporal patterns of process type and intensity interact in the development of landforms and
landscapes”.
Considering the numerous references made to Yosemite, this author finds it appropriate to
conclude on an historic, yet compelling note. According to some, the word Yosemite is a
derivation of a Native American phrase – yo-che-maté (spelled phonetically) which means ‘some
among them are killers’. How right they were. It was spoken by Native Americans to the
Mariposa Battalion as the battalion entered the area in 1851. The battalion thought they were
being told the name of the area (Personal communication with Yosemite Museum docent via
telephone, 10 May 2005). What irony that this area of such striking natural beauty carries with it
a dark connotation. I’d like to think that the Native American spirit lives deep within the
glacially sculpted landforms we have studied for more than 150 years and so admire today.
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Figure 1. Glacial polish – Yosemite National Park, October 2004
Figure 2. Glacial striae – Yosemite National Park
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Figure 3. Roche moutonnée – Lembert Dome, Yosemite National Park, October 2004
Figure 4. Subglacial meltwater – Aktineq Glacier, Bylot Island, Nunavut, Canada. Shilts, ISGS, July 1990
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Figure 5. Possible erosion by subglacial meltwater – Olmsted Point, Yosemite National Park, October 2004
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BIBLIOGRAPHY
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