Geotech Geol Eng (2009) 27:23–42
DOI 10.1007/s10706-008-9209-0
ORIGINAL PAPER
Statistical Analysis of Landslide Events in Central America
and their Run-out Distance
Graziella Devoli Æ Fabio V. De Blasio Æ
Anders Elverhøi Æ Kaare Høeg
Received: 7 June 2007 / Accepted: 20 April 2008 / Published online: 16 May 2008
Ó Springer Science+Business Media B.V. 2008
Abstract Statistical analyses of landslide deposits
from similar areas provide information on dynamics
and rheology, and are the basis for empirical relationships for the prediction of future events. In Central
America landslides represent an important threat in
both volcanic and non-volcanic areas. Data, mainly
from 348 landslides in Nicaragua, and 19 in other
Central American countries have been analyzed to
describe landslide characteristics and to search for
possible correlations and empirical relationships. The
mobility of a landslide, expressed as the ratio between
height of fall (H) and run-out distance (L) as a function
of the volume and height of fall; and the relationship
between the height of fall and run-out distance were
studied for rock falls, slides, debris flows and debris
G. Devoli (&) F. V. De Blasio A. Elverhøi K. Høeg
International Centre for Geohazards, c/o Norwegian
Geotechnical Institute, P.O. Box 3930, Ullevaal Stadion,
Oslo 0806, Norway
e-mail: [email protected]
G. Devoli F. V. De Blasio A. Elverhøi K. Høeg
Department of Geosciences, University of Oslo,
P.O. Box 1047, Blindern, Oslo 0316, Norway
F. V. De Blasio
e-mail: [email protected]
A. Elverhøi
e-mail: [email protected]
K. Høeg
e-mail: [email protected]
avalanches. The data show differences in run-out
distance and landslide mobility among different types
of landslides and between debris flows in volcanic and
non-volcanic areas. The new Central American data
add to and seem consistent with data published from
other regions. Studies combining field observations
and empirical relationships with laboratory studies and
numerical simulations will help in the development of
more reliable empirical equations for the prediction of
landslide run-out, with applications to hazard zonation
and design of optimal risk mitigation measures.
Keywords Landslides Debris flows Lahars Run-out distance Nicaragua Central America
1 Introduction
Landslides occur frequently in Central America and
almost all the countries in this region have recently
experienced catastrophic events. The landslides in
Central America are of different types and occur at a
variety of scales, but debris flows are the most frequent
type in both volcanic and non-volcanic environments
(Coe et al. 2004; Devoli et al. 2007a). Single debris
flow events in the interior mountain ranges have not so
far caused as many fatalities as those in the volcanic
chain. However, the non-volcanic debris flows sometimes occur in a group of small events that may
coalesce in a common drainage paths and flow great
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distances to alluvial fans at the base of the mountain
range, causing human casualties (Strauch 2004) and
large damage to the infrastructure and the economy of
the area (Coe et al. 2004). Volcanic debris flows,
known as lahars (Vallance 2005), are among the most
frequent types of landslides and are particularly
dangerous to life and property. In the circum-Pacific
region, about 50,000 people have been killed by lahars
in historical times (Skermer and VanDine 2005). In
Central America, there are several examples of single
volcanic landslides killing hundreds of people (e.g.
Scott et al. 2005). Lahars and large-scale volcanic
edifice collapses, called debris avalanches (Siebert
et al. 2006), can travel long distances from a volcano
and destroy or damage everything in their paths
through burial or impact, dramatically affecting landscapes, transportation routes and population centres
that are located in their proximity.
The dramatic destructive power of debris flows
derives from the high travel speed, the long run-out
distance, and the fact that precursors such as abnormal precipitation are often ignored by the local
population. After the damages produced by recent
landslides, significant effort is being made by the
scientific community to improve the knowledge about
landslides through a systematic collection of field
data and investigation, development of digital databases, and implementation of early warning systems.
As part of this commitment, it is mandatory to
understand how debris flow initiate, travel and
deposit in order to assess and mitigate the risk they
pose to the potentially affected population.
Information obtained from field surveys may be
used to quantify a set of relevant parameters that
describe the characteristics and behavior of debris
flows, such as run-out distance, inundated area, run-out
angle, peak discharge, velocity, flow depth and maximum deposit thickness and volume (Jakob 2005b;
Corominas 1996). Empirical-statistical methods, if
applied for predictive purposes in conditions similar to
those on which their development is based, offer useful
tools for predicting the run-out and extent of debris
flows and other types of landslides such as rock
avalanches (Rickenmann 2005; Legros 2002). Additionally they provide information on the rheological
properties which can find application in the mathematical modelling of mass movements. In the
development of dynamical models, the major difficulty
is the selection of appropriate friction parameters and
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Geotech Geol Eng (2009) 27:23–42
material rheology (Rickenmann 2005). The results
from empirical analyses can be used to calibrate the
input parameters in the numerical calculations of the
equations of motion for the landslide.
The present study describes the physical characteristics of landslides in Central America, and in
particular in Nicaragua, based on the available field
data. The data are analyzed and presented in form of
empirical relationships among the run-out distance,
the vertical drop, the travel angle, and landslide
volume. The Central American data are then compared with those proposed in earlier studies. The
study also highlights the differences in the observed
run-out distances and mobility among the different
types of landslides and between landslides in volcanic
and non-volcanic areas.
The data used in this study, were mainly gathered
from Nicaraguan landslides, but some events from El
Salvador, Costa Rica and Guatemala were also
included. The Nicaraguan data were taken from the
national landslide database (Devoli et al. 2007a). The
study includes all types of landslides identified in the
country such as rockfalls, rotational and translational
slides, debris flows and debris avalanches in both
non-volcanic and volcanic environments.
The study provides a statistically significant set of
data for the empirical analysis that may be used in the
evaluation of the landslide hazard in other parts of the
world with similar conditions. This work is part of a
more extensive research effort which aims to improve
the knowledge about landslides in Nicaragua, defining spatial and temporal distributions (Devoli et al.
2007a, b), physical characteristics, behavior and main
triggering mechanisms.
2 Regional Setting
Central America is a narrow isthmus (*538,000 km2)
connecting North and South America and bordered by
the Caribbean Sea to the east and the Pacific Ocean to
the west. It includes seven small countries: Guatemala,
Belize, Honduras, El Salvador, Nicaragua, Costa Rica
and Panama (Fig. 1a). Although differences exist
among these countries, common features can be
observed with respect to seismic and volcanic hazard,
climate and geology.
Geologically, the region can be divided in two
blocks. The northern block (Chortis block) containing
Geotech Geol Eng (2009) 27:23–42
25
Fig. 1 Spatial distribution
of Nicaraguan landslides
and the geomorphological
units. The delimitation of
the geomorphological units
is based on Fenzl (1989).
Landslides are represented
by blue points and orange
areas. Insert (a) shows the
map of Central America,
indicating in light grey the
countries where landslides
have also been collected.
Brown dots show the
approximate location of
volcanoes where landslides
occurred
Guatemala, Honduras, El Salvador and northern Nicaragua, is composed of Paleozoic metamorphic rocks
overlain by continental and marine Mesozoic
sequences, some local Tertiary marine sequences,
and by extensive Tertiary (Upper Miocene-Pliocene)
volcanic rocks. The southern block (Chorotega block)
extends from southern Nicaragua to Panama and is
composed of Mesozoic marine sediments and volcanic
rocks, overlain by Tertiary sedimentary rocks and by
Oligocene volcanic rocks. Intrusive bodies of Paleozoic, Mesozoic up to Tertiary age, as well as
serpentinites (Cretaceous?), have been observed in
both sectors. Pleistocene terraces and Holocene alluvium cover the Pacific and Caribbean Coastal plains
(Weyl 1980). A common feature is the Central
American Volcanic Chain that runs parallel to the
Pacific coast from Guatemala-Mexico border to Panama, superposed on the older structures and formed
after the two blocks had been sutured (Weyl 1980). The
volcanic chain is composed of active and dormant
volcanoes of Quaternary age. It is a product of the
north-east-directed subduction of the Cocos plate
beneath the Caribbean plate that occurs in the Middle
American Trench situated in the Pacific Ocean. The
largest earthquakes in the region are produced by the
convergence of these two plates, but the seismic
activity is also influenced by the interaction of other
major plates (North American, South American, and
Nazca).
The region has a tropical climate and experiences a
rainy season that begins in May and extends to October.
Because of its geographic position and geologic
setting, the region is subject to a large variety of natural
phenomena such as tropical cyclones, droughts, floods,
landslides, earthquakes, volcanic eruptions, and tsunamis. Landslides occur on slopes of active and
dormant volcanoes composed of Quaternary volcanic
rocks, which are frequently hydrothermally altered,
and on the mountain ranges of the interior on steep
slopes composed of highly weathered soil and rocks
(Paleozoic metamorphic rocks, Tertiary volcanic and
sedimentary rocks). Landslides take place primarily
during the wet season and are triggered by intensive
rainfalls sometimes associated with tropical cyclones.
They may also be triggered during the dry season by
earthquakes and volcanic eruptions.
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26
3 Data Sources and Criteria for Selection
Landslide studies in Nicaragua only started a decade
ago and have focussed mainly on the events associated with Hurricane Mitch that struck Central
America in October 1998. The Nicaraguan landslide
data used in this study were obtained from the
national landslide database which is currently under
development and updating at Instituto Nicaragüense
de Estudios Territoriales (Nicaraguan Geosciences
Institute, INETER), the national government institution responsible for landslide investigation, mapping,
and monitoring as well as dissemination of landslide
information, public awareness and emergency
response.
The data are from the first update of the database
that includes all data available up to 2005, but
temporally distributed from 1826 to 2003 (Devoli
et al. 2007a, b). The database includes more than
17,000 events. A second updating of the database is
in progress with the aim to integrate landslide events
that occurred after 2003. The data contained in the
database have been compiled from multiple sources
such as newspapers, technical reports and landslide
inventory maps. They are recorded in the form of
spatial data represented by geo-referenced points and
by polygons.
Different methodologies have been used to map
and collect the original information, and hence, the
type and quality of available information in the
database are variable and heterogeneous. Important
parameters needed for the debris flow analysis such
as volume, run-out distance, peak discharge, inundated area, or velocity have not been collected
systematically and all are not always available, either
because they were not measured in the original
sources, or because they have not been entered in the
database. As a consequence only those cases with
available geometric parameters already in the database or available in the original sources were used in
the statistical analysis. The rejected cases included
those where key parameters were missing or, were
difficult to estimate with sufficient accuracy, where
the data were obtained only from historical sources
such as newspapers, where reported data deviated
from field observations or were contradictory, or
where metadata such as the location of a measurement were missing. A large number of records
(16,785 events) did not contain parameters required
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Geotech Geol Eng (2009) 27:23–42
for the analysis. Therefore, the sample used (348
events) in this study is not representative of the total
amount (17,133 events) of landslides recorded so far
in the country.
Most of the events used in this study were mapped
during the AECI project (INETER-AECI 2004) and
the PRRAC project (Álvarez et al. 2003a) (Table 1).
The events mapped by the first author during 4 years
(from 1999 to 2003) of systematic observations by
INETER were also included. The events analyzed are
spatially distributed along the Pacific Volcanic Chain
and in the Interior Highlands, especially in the
northern region in the Department of Nueva Segovia,
with a few events located in the central region close
to the towns of Telpaneca, Estelı́ and Esquipulas
(Fig. 1). Few data (19 events) are available for the
other Central American countries (Fig. 1a). The
landslide data for Guatemala, El Salvador and Costa
Rica (Table 1) were extracted from Siebert et al.
(2006), Crosta et al. (2005), and Alvarado et al.
(2004).
4 Types of Landslides and Terminology
The term ‘‘landslide’’ in this paper is used to describe
all types of mass movements. For the purpose of this
study the landslides have been classified under the
main categories falls, slides and flows, and the flowlike landslides have been subdivided into three subcategories.
4.1 Rock Falls and Slides
The terminology used to describe falls and slides
follows that proposed by Cruden and Varnes (1996),
based on the type of material and type of movement. In
Nicaragua, rock falls and earth falls start as abrupt and
rapid detachment of a single mass, or a group of rocks.
They occur on steep man-made slopes (i.e. Cuesta del
Plomo) or on natural slopes like the inner walls of
calderas (i.e. Apoyo), craters (i.e. Cosigüina), or small
hills which are the remains of collapsed old volcanic
edifices. Rock and earth falls are triggered by earthquakes, rainfalls and human activities and frequently
affect roads and touristic infrastructures (national
parks and lake resorts) located in the proximity of
calderas and craters. Few of them affect urban areas.
Those triggered by human activities have occurred
El Salvador
El Salvador
El Salvador
El Salvador
El Salvador
El Salvador
Guatemala
Guatemala
Guatemala
Guatemala
Guatemala
Guatemala
Guatemala
DA_V
DA_V
DF_V
DF_V
FS
FS
DA_V
DA_V
DA_V
DA_V
DA_V
DA_V
DF_V
Costa Rica
DA_V
Costa Rica
Costa Rica
DA_V
Costa Rica
Costa Rica
DA_V
DA_V
Costa Rica
DA_V
DA_V
Country
Type
Tolimán volcano
(Panabaj 2005)
Tecuamburro volcano
Pacaya volcano
(Rı́o Metapa)
Fuego/Acatenango volcano
(Escuintla)
Acatenango volcano
(La Democracia)
Almolonga volcano
(Cerro Quemado)
Tacaná volcano
(Agua Caliente)
Cordillera del BalsamoCerro San Jacinto
Cordillera del Balsamo
(Las Colinas)
San Salvador volcano
(Montebello)
San Vicente volcano
San Vicente volcano
(Tecoluca)
Santa Ana volcano
(Acajutla)
Turrialba volcano
(Angostura)
Irazú volcano (Prusia)
Tenorio volcano (Tierras
Morenas)
Miravalles volcano
(La Fortuna)
Rincón de la Vieja volcano
(Azufrales)
Cacao-Orosı́ volcano
(Quebrada Grande)
Location
15 Sep. 2001
5 Oct. 2005
100–38.3 ka
1.6–0.6 ka
30–8.5 ka?
70–43 ka
*1.2 ka
26.3–10.6 ka
10 Oct. 1986
13 Jan. 2001
19 Sep. 1982
1480
1800
2500
4000
3780
780
2800
85
158
1050
1080
2160
1920
\56.9
Pleistocene
884
2465
1622
2057
1095
1408
H
(m)
17 ka
Holocene
Pleistocene
8.3 ka
Pleistocene
Pleistocene
Age
Table 1 List of Central American landslides used in the analysis
45,00
15,000
25,000
50,000
42,000
6000
0.328
0.120
0.100
0.080
0.090
0.130
0.350
[8000
0.197
0.228
0.193
0.090
0.040
0.062
0.145
0.069
0.110
0.123
0.088
H/L
0.190
Lmax
(m)
440
800
4600
5600
24,000
48,000
14,250
17,000
23,500
18,700
8900
16,000
L
(m)
4E+05
4E+09
1E+09
2E+10
5E+09
1E+08
1E+09
8000
2E+05
3E+05
1E+05
1E+09
2E+10
1E+09
2E+09
2E+09
8E+09
4E+08
2E+09
V (m3)
2.57
55
[1
(*4)
440
210
13
6
540
15–25
5.2
80–118
92–127
11–18
36–52
A
(km2)
15
5
0.1
1
[[1]
16 ± 5
0.75–1.4
1.35–2.0
1.6–2.36
6.0–8.2
0.2–0.36
1.4–2.0
V ranges
(km3)
Connor et al. (2006)
Siebert et al. (2006)
Siebert et al. (2006)
Siebert et al. (2006)
Siebert et al. (2006)
Siebert et al. (2006)
Siebert et al. (2006)
Rymer (1987)
Crosta et al. (2005)
Blanco et al. (2002)
Blanco et al. (2002)
Siebert et al. (2006)
Siebert et al. (2006)
Alvarado et al. (2004)
Alvarado et al. (2004)
Alvarado et al. (2004)
Alvarado et al. (2004)
Alvarado et al. (2004)
Alvarado et al. (2004)
References
TOL
TEC
PAC5
FUE
ACA
ALM
TAC
CSJ
COL
ES2
ES1
SV
SA
TUR
IRA
TEN
MIR
RV
CAC
Event
Geotech Geol Eng (2009) 27:23–42
27
123
123
Nicaragua
Nicaragua
Nicaragua
Nicaragua
Nicaragua
Nicaragua
Nicaragua
Nicaragua
Nicaragua
DF_V
DF_V
DF_V
DF_V
DF_V
DF_V
DF_V
DF_V
RF
05 Apr. 2003
30 Oct. 1998
May 2000
May 2000
May 2000
May 2000
2001
L
(m)
1370
1340
96
450
0.266 1E+05
4500 15000
0.296 51,000
4700 15,000 0.285 3E+05
4650 17,000 0.288 5E+05
3077 15,000 0.318 1E+05
5000
0.314 2E+05
0.304 3E+05
0.335 2E+06
0.519 2000
0.391 2E+06
0.101 1E+09
20
36
0.556 96
(1)
(1)
45?
60
93
85
352/353
214 (CAS)
81
80
Event
Devoli et al. (2007a)
Scott et al. (2005)
Devoli et al. (2007a)
Devoli et al. (2007a)
Devoli et al. (2007a)
Devoli et al. (2007a)
Devoli et al. (2007a)
46
214 (CAS-DF)
211
210
209
205
158
Álvarez et al. (2003b) 154
Devoli et al. (2007a)
Devoli et al. (2007a)
Álvarez et al. (2003a)
Scott et al. (2005)
Ui (1983)
Ui (1983)
V (m3) V ranges A
References
(km2)
(km3)
0.092 1E+09
H/L
1125 10,000 25,000 0.113 3E+06
1330
1340
1340
980
1330
Lmax
(m)
4400 5500
4500
4000
185
1150
1270 12,600
1260 13,700
H
(m)
28, 31 Oct. 2002 1380
1993?
Apr. 1979
Oct. 1998
30 Oct. 1998
Holocene
1570
Age
The list shows only the events with available volume values. The data are listed by country and by landslide type. Abbreviations: DA_V: Volcanic debris avalanches; DF_V:
Volcanic debris flows; FS; Flowslides; DF_NV: Non-volcanic debris flows; RF: Rock falls
Cuesta El Plomo
Casita volcano (Southern
slope)
San Cristóbal volcano
(El Corazón-east)
San Cristóbal volcano
(El Corazón)
San Cristóbal volcano
(El Corazón-west)
San Cristóbal volcano
(Las Rojas-La Suiza)
San Cristóbal volcano
(El Corazón)
Concepción volcano
(La Chirca)
Concepción volcano
(San José del Sur)
Concepción volcano
(San José del Sur)
Casita volcano (Southern
slope)
Nicaragua
Nicaragua
DA_V
Mombacho volcano
(Las Isletas)
DF_V
Nicaragua
DA_V
Mombacho volcano
(El Cráter)
Ocotal
Nicaragua
DA_V
Location
DF_NV Nicaragua
Country
Type
Table 1 continued
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Geotech Geol Eng (2009) 27:23–42
Geotech Geol Eng (2009) 27:23–42
along roads or inside gold mines (northeast of Nicaragua). The 13 rockfall events considered in the present
analysis involved Holocene andesitic lavas and ignimbrites, Paleozoic metamorphic rocks, or Tertiary
volcanic rocks of the Coyol and Matagalpa formations.
The run-out distances varied from 12 to 870 m. The
volume is known for only one event.
Slides are down-slope movements of soil or rock
mass occurring dominantly on a distinct surface of
rupture that can be curved, concavely upward (rotational slides) or planar (planar or traslational slides). In
Nicaragua, slides are frequent along roads, in unpopulated areas, along stream banks or in open slopes
affecting communication lines and agricultural areas
used for crops (coffee plantations, beans, corn) and
pasture fields. Eighty-one translational and rotational
slides were considered in the present analysis. Most of
them occurred in the northern and central region of
Nicaragua and only two of them belonged to the
volcanic chain. Although classified as translational and
rotational slides, most of them could also be classified
as complex slides where the event may transform
progressively from a slide to an earth or debris flow.
The slides usually occur on slopes ranging between 20°
and 43°. The rocks involved are Paleozoic metamorphic units (schists and phyllites), Tertiary volcanic
rocks (basalts, ignimbrites, andesites, dacites), colluvial deposits and soil of Holocene age. The run-out
distances vary from 20 m to 2.5 km and the depth of
the initial failure surface is generally [10 m. Most of
these landslides are now considered inactive.
4.2 Flow-like Landslides
To classify ‘‘flows’’ several classifications have been
proposed based on the type of material, style and rate of
movements, morphology, sedimentology of deposits,
and thresholds in rheologic behavior (Pieson and Costa
1987; Hungr 2005). Consequently, at international
level there is a confused state of terminology for flowlike landslides (Hungr 2005) and different terms are
sometimes used to describe the same event in volcanic
environments (Vallance 2005). The terminology used
to describe debris flows follows in general that of
Cruden and Varnes (1996) and Hungr et al. (2001), but
for flows in volcanic areas the terminology proposed by
Vallance (2000) is preferred.
In this study debris flows, flowslides and debris
avalanches were analyzed. Other types of flows (i.e.
29
mud flows, and earth flows) have occurred in
Nicaragua, but they were not considered for the
present analysis because of the lack of data.
4.2.1 Debris Flows
Debris flows are extremely rapid flows of a saturated
mixture of debris and water in a steep channel. The
mixture of debris and water has a sediment concentration[60% by volume or 80% by weight with a density
resembling wet concrete. Sediments involved are
poorly sorted ranging from clay to boulders. Significant proportions of organic material, including logs
and, tree stumps can be present in the mixture. They
occur in channels and are characterized by an initiation, transport and deposition zone. Although they
usually initiate in unpopulated areas, debris flows are
highly destructive because they affect roads, bridges
and settlements located far away from their source.
In this study, the term debris flow is prefaced with
non-volcanic to indicate an event occurring in the
mountain ranges of the interior, and volcanic to
indicate those occurring on slopes of quaternary
volcanoes and other volcanic structures (i.e. calderas), with the dominant clastic component volcanic in
origin.
4.2.1.1 Non-volcanic debris flows The nonvolcanic debris flows analyzed, have occurred in the
mountainous slopes of the Interior Highlands,
involving soil, colluvium and weathered rocks
(schists, phyllites, ignimbrites, conglomerates) of
Paleozoic and Tertiary age. A shallow failure surface
(in general \10 m deep) was observed, especially for
the youngest events. In some cases they were initiated
as shallow planar slides or rotational slides. Most of the
224 events occurred in the Department of Nueva
Segovia, with a few events in the central region in the
municipalities of Telpaneca and Estelı́. They occurred
in unpopulated areas along slopes between 16° and 60°
reaching run-out distances up to 1.5 km. Volume
estimation is available only for one event. Most of the
events were triggered by rainfall associated with
Hurricane Mitch, and in general occurred on top of
older landslides (in proximity of the old scarp or in the
frontal part) or in deforested areas.
4.2.1.2 Volcanic debris flows The volcanic debris
flows can differ from the non-volcanic ones in origin
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30
and size, and show downstream evolutions less
commonly observed in debris flows from other
environments (Vallance 2005). They are also called
‘‘lahars’’ which is a term referring to the event and
not the deposit produced by it (Vallance 2000). The
term lahar includes a high-sediment-fraction volcanic
debris flow (debris flow phase), a low-sedimentfraction hyperconcentrated flow (hyperconcentrated
flow phase), and a muddy streamflow phase. In the
debris flow phase the solid and liquid fractions are
approximately equal volumetrically and in a vertical
section they move downstream approximately in
unison. The muddy (silt and clay) stream flow phase
is characterized by fine-grained sediments which
move in suspension with the fluid (suspended load),
and coarse-grained sediments that move along the
bed at discrete intervals (bedload) (Vallance 2005).
The hyperconcentrated flow phase (or transitional
flow phase), which is intermediate between debris
flow and streamflow, is characterized by a mixture of
non-uniform debris and water having a water content
larger than that of debris flow but less than that of
muddy streamflow. The flow possesses fluvial
characteristics but can carry very high sediment
loads. The sediment concentration is between 20%
and 60% of the volume (Pierson and Costa 1987;
Vallance 2000, 2005). The transitions between phases
are gradational and dependent on other factors like
sediment-size distribution and energy of the flow.
Volcanic debris flows can be subdivided into two
types based on the clay content (Scott 1988; Scott et al.
1995, 2001; Vallance and Scott 1997). Clay-rich
(cohesive) volcanic debris flows have a matrix composed of a mix of sand and silt and contain more than 3–
5% clay-size sediment. They typically begin with slope
failures caused by tectonic earthquakes, or simple
gravitational collapse, hydrovolcanic activity, or
intense precipitation. They form by collapse of
water-saturated, hydrothermally altered volcanic
deposits (e.g. debris avalanches) that rapidly transform
downstream to debris flows. Clay-poor (non-cohesive
or granular) volcanic debris flows have a matrix
composed of silty sand and contain \3–5% clay-size
sediments. They can be triggered by eruption-induced
meltwater surges, lake breakouts, eruptions through
crater lakes, and intense rainfall. They commonly
initiate as water floods and transform into debris flows
by incorporating sediment through erosion. They can
transform downstream to more dilute flows.
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The 27 volcanic debris flow events considered in
this study occurred along the steep slopes and gullies
of active and dormant volcanoes (Concepción, San
Cristobal, Maderas and Casita), along inner walls of
the caldera of Apoyo, and in small hills remaining
after volcanic collapses, such as Cerro Los Martı́nez
close to the capital Managua. They occurred between
1979 and 2002, were triggered by rainfall, and
involved loose pyroclastic material, blocks of lavas,
tuffs and ashes of Holocene age. The events that
occurred in the inner walls of calderas or in small
hills resulting from volcanic collapses, had maximum
run-out distances of about 500 m. The events
occurred in active volcanoes (i.e. San Cristóbal and
Concepción), started as water floods and transformed
into debris flows, eroding and incorporating loose
pyroclastic material deposited on the slopes during
recent eruptions. Some events were triggered by
intense and local rainfall during an eruption or
following an eruption, other events by an intense
and prolonged rainfall associated with hurricanes and
tropical depressions. For a few events the combination of microseismicity, hydrothermal activity
preceding an eruption, and rainfall was identified as
the triggering mechanism. In these events the debris
flow phase is easily identified, but hyperconcentrated
phase is rarely distinguishable from muddy streamflow. The volume was in general \1.5 million m3
and the run-out distance of the debris flow phase was
\10 km. For some lahars the measured maximum
run-out distance includes the hyperconcentrated and
muddy streamflow phase and in those cases the runout distance was about 15–16 km. Geotechnical
classification tests have been performed to characterize the material from the San Cristóbal volcano
(Heyerdahl et al. 2003). Samples were collected in
two main gullies where debris flows occurred in 2000
(Event # 210 in Table 1). The deposits consisted of
large blocks of 1–2 m diameter, cobbles, pebbles, and
sand in a very mixed state. Clay and silt fractions
were almost completely absent. The grain size
distribution of the source area was similar to that of
the deposit area, with particles in the sand fraction,
but also gravel and larger particles were present.
The lahars on slopes of dormant and deeply eroded
volcanoes (Casita and Maderas) began with the failure
of water-saturated and hydrothermally altered volcanic
deposits and transformed into debris flows. In the 1998
lahar at the Casita volcano, Scott et al. (2005)
Geotech Geol Eng (2009) 27:23–42
identified several phases: landslide phase, debris
avalanche phase, transitional or hyperconcentratedflow phase, debris flows phase, transitional or hyperconcentrated-flow phase and streamflow phase. The
run-out distance of the debris flow phase was about
10 km, but the hyperconcentrated and muddy streamflow phase had a run-out distance of about 25 km. The
deposit of the first hyperconcentrated flow consists of
clasts of pebble size in a sandy matrix with few larger
clasts. The percentage of silt and clay is about 2%. The
debris flow deposit is massive and consists of a coarse
phase of pebble size clasts with variable proportions of
cobbles dispersed or floating in a muddy matrix. The
observed boulders have diameter of about 4 m. The
grain size distribution is bimodal with sorting value
increasing downstream. Silt and clay constitute, on
average, 18% of the deposits. The clay is derived from
the hydrothermal alteration within the edifice. The
distal run-out deposit (hyperconcentrated and stream
flow phase) is thin and texturally indistinguishable
from the overbank layers of sandy silt and gravel bars
in the channels (Scott et al. 2005).
In the statistical analyses described in Sect. 5, three
lahars from the neighboring countries of El Salvador
and from Guatemala were also included. The two
events from El Salvador, which occurred in 1982 at the
San Salvador volcano and in 2001 at the San Vicente
volcano, were both triggered by intense rainfall. Both
events occurred in volcanic rocks of Holocene age and
reached a distance of about 5 km from their sources.
The event from Guatemala occurred in 2005 at the
Tolimán volcano and was triggered by intense rainfall
during Hurricane Stan. The run-out distance for this
event was also about 5 km.
4.2.2 Flowslides
Flowslides are characterized by the suddenness of
failure, following some disturbance, and a rapid and
extensive run-out over gentle or horizontal ground.
They involve cohesionless or, weakly cemented
materials of high porosity (Evans and Bent 2004)
and usually come to rest abruptly. In the present
analysis, two examples from El Salvador were
considered. They occurred along the coastal cordillera
(Cordillera del Balsamo), triggered by earthquakes in
1986 and 2001. They involved poorly consolidated
volcanic tuff and stratified volcanic deposits of the
Balsamo, Cuscatlán and San Salvador Formations of
31
Miocene to Holocene age (Rymer 1987; Evans and
Bent 2004; Crosta et al. 2005).
4.2.3 Debris Avalanches
The term ‘‘debris avalanche’’ is used in the literature to
indicate a variety of very rapid to extremely rapid flow
processes that often occur on open-slope without
confinement in an established channel. Cruden and
Varnes (1996) refer to them as to larger events. In
contrast Hungr et al. (2001) define them as shallow
flow of partially or fully saturated debris on a steep
slope. In volcanic environments the same term is used
to describe large slope failures that exhibit some
combination of slide- and flow-like character. Schuster
and Crandell (1984) used for the first time the term at
volcanoes referring to a sudden and very rapid flow of
incoherent, unsorted mixture of rock and soil in
response to gravity. Vallance (2005) added that debris
avalanches are not water saturated flows and the load is
entirely supported by particle-particle interactions.
The definition proposed by Hungr et al. (2001)
describes well the non-volcanic shallow debris avalanches triggered by rainfalls on steep and open slopes
of the Interior Highlands in Nicaragua. In contrast, the
debris avalanches on volcano slopes differ in magnitude, triggering mechanisms, deposition patterns and
distance travelled and conform better to the descriptions by Ui et al. (2000), Siebert et al. (1987), Naranjo
and Francis (1987), Crandell (1989), Glicken (1998),
Capra et al. (2002). Volcanic debris avalanches are
produced from a sector collapse of a volcanic edifice,
triggered by intrusion of new magma, a phreatic
explosion or an earthquake (Ui et al. 2000). Sector
collapses are large volcanic landslides that remove the
summit of the failed volcano and leave an open,
horseshoe-shaped (amphitheatre) crater. The deposit
has a characteristic hummocky topography on the
surface and its texture is defined by two end member
facies, namely block and mixed (matrix) facies (Glicken 1998). The volume of these events is generally in
excess of 1 km3 (Ui et al. 2000). However, volcanic
debris avalanches are also a common middle stage in
the transformation of a cohesive debris flow from a
landslide or rockslide (Scott et al. 2001). Smaller
debris avalanches (also known as flank collapses) that
do not include the volcano summit may also occur and
can produce debris flows, such as the 1998 Casita event
(Scott et al. 2001).
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32
Non-volcanic debris avalanches were not analyzed
because of lack of data. Three volcanic debris
avalanches from Nicaragua were included in this
study. Evidence of volcanic debris avalanches in
Nicaragua have been found only at two volcanoes. At
the Casita volcano a small debris avalanche (described
as flank collapse by Scott et al. 2005) occurred in 1998
with a volume of 1.6 million m3 and a run-out of about
1.1 km, transforming into a catastrophic debris flow.
The deposit consists of a coarse granular fraction with
subordinate granular matrix (Scott et al. 2005). It has a
locally intact framework of cobbles and boulders with
subordinate interstitial pebbles and finer sediment, and
contains a small proportion of silt and clay (2%). At the
Mombacho volcano one debris avalanche (Avalancha
Las Isletas) occurred in prehistoric times on the
northern slope, and another one (Avalancha El Cráter)
in 1570 on the southern slope caused the death of 400
people. Both were produced from sector collapses and
have a run-out distance of about 12–13 km from their
sources, and a volume approximately of 1 km3 (Ui
1983). Similar debris avalanches have been recently
identified elsewhere in Central America and some of
them are considered in this analysis (Table 1). From
Costa Rica seven deposits of debris avalanches that
occurred in prehistoric times on the volcanoes Cacao,
Tenorio, Miravalles, Turrialba, Rincón de la Vieja and
Irazú, with run-out distances ranging between 6 and
20 km, were included in the analyses (Alvarado et al.
2000, 2004). Also included in the analyses were six
debris avalanches in Guatemala, which occurred on the
volcanoes Tacaná, Almolonga, Acatenango, Fuego,
Fig. 2 Sketch of landslide
deposit and failing mass,
and definition of the
parameters used in the
present analysis: (A)
position of the starting
point; (B) position of the
lowest point; (H) height of
fall; (L) run-out distance;
(Lmax) maximum run-out
distance shown for volcanic
debris flows; (b) slope
angle; (a) travel distance
angle
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Geotech Geol Eng (2009) 27:23–42
Pacaya and Tecuamburro, with run-out distances
ranging between 6 to 50 km; as well as two debris
avalanches in El Salvador, which occurred on Santa
Ana and San Vicente volcanoes with run-outs[20 km
(Siebert et al. 2006).
5 Parameters Considered in Correlation Analyses
The parameters considered for the analysis are
presented on Fig. 2. The difference between the
highest altitude of the source area and the lowest
altitude of the deposit along the run-out path represents the height of fall (H) or vertical drop. This
corresponds to the total drop height defined by Legros
(2002) and to the collapse height defined by Ui
(1983) for volcanic debris avalanches. The highest
point of the pre-avalanche volcanic edifice is sometimes hard to assign for a volcanic debris avalanche
because of the failure of the volcanic edifice that
produced the avalanche. In these cases the highest
point of the present crater rim or present summit of
volcano was used (as proposed by Ui et al. 1986).
The horizontal projection of the distance between the
starting point and the lowest point of the sliding mass
is defined here as the run-out distance (L), also
known as the total travel distance (Rickenmann
2005). For debris flows the estimate of this parameter
is somewhat subjective. Some surveyors define runout distance as the limit of fine sediment deposition
while others use the term for the extent of coarse
debris (Jakob 2005a). For some Nicaraguan volcanic
Geotech Geol Eng (2009) 27:23–42
debris flows two run-out distance estimates are
recorded in the database. One value refers to the
run-out distance of the debris flow phase, while the
other refers to the maximum run-out distance (Lmax)
that may include an hyperconcentrated/muddy stream
flow phase, characterized by fine sediments (Fig. 2).
These measurements are available only for the events
that were mapped immediately after their occurrence.
In the analysis presented below, L refers to the
maximum run-out distance (Lmax) for rock falls,
slides, non-volcanic debris flows and volcanic debris
avalanches, while for volcanic debris flows L refers
to the distance L in Fig. 2 (run-out distance of the
debris flows phase) and not the maximum run-out
distance of the event. This was done for two reasons:
most of the observed damages are within the area
where coarse debris prevails and more consistent
comparison can be done with those cases where the
end location of the fine sediments was not measured.
The travel distance angle (fahrböschung), also
called run-out angle or reach angle (a), is the angle of
the line connecting the head of the landslide source to
the distal margin of the displaced debris mass. The
tangent of this angle, termed run-out ratio or apparent
friction coefficient, is the ratio H/L between the height
of fall and the run-out distance. For a sliding body, it is
the apparent coefficient of friction at the surface of
contact between the sliding mass and the ground that is
commonly used to describe landslide mobility (Scheidegger 1973; Corominas 1996; Rickenmann 2005;
Legros 2002). The debris flow volume may change in
time and depends on three factors: the volume of the
initial failure mass, the volume entrained along the
transport reach, and the volume deposited (Jakob
2005b). In our study the volume (V) refers to the latter.
This was estimated by multiplying the area covered by
the deposit with an approximate thickness. For recent
debris flows the cross sections along the path and the
inundated area are available and these were used in the
estimation of the volume.
6 Results of Analyses
6.1 Relationship Between the Height of Fall and
Run-out Distance
The first analysis looked at the relationship between
the run-out distance L and the height of fall H
33
(Figs. 3 and 4). Different mechanisms of failure, rock
types and geomorphological environments were considered. A similar analysis was done by Corominas
(1996) for different landslide types, and by Ui (1983)
for volcanic debris avalanches. The rock falls and
slides (Fig. 3) and debris flows and flowslides
(Fig. 4) were analyzed separately.
The correlation between H and L shows a linear
trend for rock falls and slides (Fig. 3) with an
exponent close to one. For rock falls (Fig. 3a) the best
interpolation obtained with the standard leasts square
regression method gives the empirical relationship
log L = 0.8653log H + 0.5085 with a coefficient of
determination r2 = 0.8599, where L and H are in
meters. The standard deviation is 0.21. The equation
can also be approximated as L = 3.22 H0.865 indicating that the run-out distance is proportional to the
height of fall for this type of landslides. For slides
(Fig. 3b) a better fit is obtained with log
L = 1.1172log H + 0.228 or L = 1069 H1.117, with
r2 = 0.8526 and a standard deviation equal to 0.22.
The analysis of debris flows and flowslides was done
with a total number of 256 events and the results are
presented in both arithmetic (Fig. 4a) and log-log plots
(Fig. 4b). Non-volcanic debris flows fall in the left
corner of the plot limited by a height of fall of about
500 m and a run-out \1500 m. Slides and rock falls
data analyzed in the previous plot (Fig. 3) also fall in
this corner of the plot. The data for slides and nonvolcanic debris flows plot below the rockfalls and show
a higher mobility. Volcanic debris flows fall mainly in
the upper part of the plot with only a few events in the
left corner. Vallance (2005) emphasized that volcanic
debris flows exhibit a different behavior, especially in
terms of the distance travelled, compared to nonvolcanic debris flows. This difference in run-out
distance is apparently due to the abundance of loose
debris on steep slopes and aprons of volcanoes, and the
presence of weakened, hydrothermally altered rocks
that can be easily eroded during post-eruptive rainfall
and entrained along the path of the debris flow,
increasing substantially the initial volume (Vallance
2000). The data plotted on Fig. 4 imply that volcanic
debris flows have greater mobility than non-volcanic
ones. However, because of the gap in data for debris
flows with height of fall between 500 and 800 m, a
definite conclusion cannot be drawn. Although all
debris flows along the quaternary volcanic chain were
classified as volcanic, along this unit it is possible to
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Geotech Geol Eng (2009) 27:23–42
Fig. 3 Relationship
between the height of fall
and the run-out distance for:
(a) rock falls (13) and (b)
slides (81)
find different types of volcanic structures that differ in
shape and elevation (i.e. strato-volcanoes, cinder
cones, caldera, craters, small hills remaining from old
collapses). This difference in topography is highlighted by the plotted data. The events that occurred in
isolated cones (strato-volcanoes actives or dormant)
are located in the upper right part of the plot on Fig. 4,
while those that occurred in inner walls of calderas,
craters, and remains of old collapses are located in the
lower left part of the plot. Obviously, for these events,
the available H is lower than that available in isolated
cones, hence the run-out distance is lower and limited
by the topography. When the height of fall and the
topography are similar, the material properties seem to
123
influence the run-out distance. The Las Colinas
flowslide (COL) has a longer run-out than the debris
flow indicated as event 8202, which occurred at the
Apoyo caldera. The former involved stratified fine
volcanic deposits, while the latter occurred in a slope
composed of heterogeneous coarser material like
ignimbrites, fractured lavas, and colluvium. This
suggests that, besides landslide volume and height of
fall, other factors such as material properties, slope
geometry, slope inclination, topographic obstacles and
topographic constraints (bends, deflection, opposing
wall) along the path also affect the debris flow run-out
distance (Corominas 1996; Finlay et al. 1999; Okura
et al. 2003).
Geotech Geol Eng (2009) 27:23–42
35
Fig. 4 Relationship
between the height of fall
and the run-out distance for
debris flows
Trend lines for slides and non-volcanic debris flows
are very close for run-out distances shorter than 1 km.
To curve-fit the data in Fig. 4, the empirical relationship H = DH[1 - exp(-bL)] with DH = 1600 m;
b = 0.00033 m-1, was obtained by visual method.
This functional form gives a near linear relationship
between H and L for a run-out distance less than 4 km,
but it flattens out for greater distances indicating that
different run-out distances may be reached with the
same height of fall. More useful for practical purposes
is the inverse relationship:
H
L ¼ 3000 ln 1 1600
where L and H are in meters. In this equation a value
H [1550 m should not be used. The standard
deviation is about 610 m strongly influenced by the
outliner indicated as CAS. The coefficient of determination r2 is 0.86.
The available data were scrutinized to identify the
important factors that could influence the run-out
distance and the ratio H/L. In particular, attention was
focused on events that occurred on the same volcano
(or even in the same channel) and reached different
run-out distances, like the events 8414 and 8405 on
the San Cristóbal volcano, plotted in the right upper
part of the plot on Fig. 4, and those indicated as
events 205, 207, 210. For the events with longer runout (i.e. events 8414 and 8405) volume estimates are
not available. Therefore it is not possible to document
that the longer run-out distance corresponds to a
higher volume. However, one has made the
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36
observation that they occurred during Hurricane
Mitch (rainfall intensity *500 mm/24 h) and the
amount of water available during these events was
much higher than the amount of water available
during the events that occurred at the same volcano
triggered by local intense rainfall (*54 mm/24 h). It
is likely that the run-out distance is rather sensitive to
the amount of water available during the event, but
this assumption cannot be proved because of the
limited data available.
6.2 Relationship Between the Apparent
Coefficient of Friction and the Height of Fall
Figure 5 shows the relationship between the apparent
friction coefficient H/L and the height of fall H. The
ratio H/L is often used as a measure of landslide
mobility. The figure shows the range of values of H/L
for the different types of landslides considered in the
present analysis. Rock falls and rock avalanches,
rotational and planar slides, and non-volcanic debris
flows show a large range of H/L with values between
0.04 and 1.6. Volcanic debris flows have a ratio H/L
between 0.11 and 0.5, and flow slides have an H/L
value of about 0.19. For volcanic debris avalanches the
ratio H/L is between 0.04 and 0.14 for those formed
from sector collapses (upper left part of the plot).
Debris avalanches formed from small flank collapses
show a higher H/L of about 0.35 (indicated as CAS and
TAC in the figure). The figure shows that, for the same
Fig. 5 Apparent coefficient
of friction plotted against
the height of fall for all
types of landslides
considered. The analysis
was done with 367 landslide
data, small non-volcanic
debris flows with H \ 10
were not included
(Abbreviations:
CAS = Casita; COL = Las
Colinas; TAC = Tacaná)
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Geotech Geol Eng (2009) 27:23–42
height of fall, different values of H/L (i.e. mobility) can
be found, demonstrating that the height of fall alone is
not sufficient for predicting the run-out distance,
especially in non-volcanic areas. This is in agreement
with the findings by Corominas (1996).
6.3 Relationship Between the Apparent
Coefficient of Friction and the Landslide
Volume
The correlation between landslide volumes and apparent coefficient of friction has previously been
extensively studied for large rock avalanches with
volumes from 0.1 to 1 million m3 (Scheidegger 1973;
Li 1983; Legros 2002). For volcanic debris avalanches,
relationships have been proposed by Ui (1983),
Schuster and Crandell (1984), and Siebert et al.
1987. More recently, similar relationships have been
investigated for landslides with volumes less than
0.1 million m3 (Corominas 1996; Fannin and Wise
1996; Rickenmann 2005) and for small landslides in
man-made slopes (Finlay et al. 1999). A plot of H/L
versus volume is presented on Fig. 6 for the Central
American data. Unfortunately, the number of estimated volumes available is small, and this represents
an important limitation in the analysis. Only 33
landslides with different mechanisms of failure ranging from rockfalls, debris flows, flow slides and
volcanic debris avalanches were included in the
analysis. As already pointed out by previous authors,
Geotech Geol Eng (2009) 27:23–42
37
Fig. 6 Relationship
between the apparent
coefficient of friction and
landslide volume
the ratio H/L shows a clear tendency to decrease with
increasing landslide volume. The ratio H/L is often
used to describe the mobility of a landslide, it may be
seen that volcanic debris flows and volcanic debris
avalanches exhibit greater mobility than non-volcanic
debris flows and rock falls. Nicaraguan volcanic debris
flows are consistent with the ones from the other
Central American countries. The volcanic debris
avalanches also show consistency among Central
American countries. The volcanic debris avalanches
started as sector collapses, fall in the same lower right
part of the plot. The outlier data point (CAS_DA)
shows a higher H/L and corresponds to the small Casita
debris avalanche. For the event indicated as TAC
reported by Siebert et al. (2006) the reason for the high
value of H/L is not clear. Nor is it known whether the
event is a small flank collapse. For the 1998 Casita lahar,
the three main phases (debris avalanche, debris flow and
hyperconcentrated flows) of the event are distinguished
in the plot. This event, which started as a debris
avalanche, had longer run-out distance and involved
more volume than the events which started as normal
water flows and have characteristics of non-cohesive
debris flows, like the one indicated as event 210.
In order to check the consistency of the Central
American data with those presented by other researchers, data reported in several references were collected
(Rickenmann 2005; Corominas 1996; Scheidegger
1973; Hsü 1975; Hayashi and Self 1992; Li 1983; Ui
1983; Siebert et al. 1987; Capra et al. 2002; Evans
et al. 2005; Vallance and Scott 1997; Iverson 1997;
Kanji et al. 2003; Legros 2002). These sources
included data for 527 events. The landslide types
considered were rock falls and rock avalanches, planar
slides, debris flows and debris avalanches in volcanic
and non-volcanic environments, earthflows and mudflows. Figure 7 compares the H/L vs. volume
relationships of the international data with the Central
American data. The linear negative correlation observed
is consistent with the data available in the literature. For
Central American data the best interpolation obtained
with the standard leasts square regression method gives
an empirical relationship log H/L = -0.1047 logV
-0.0253 having a coefficient of determination
r2 = 0.692. The relation can be also expressed as
L = 1.06V0.105 H. The standard deviation for these data
was found equal to 0.16. For the international data the
best fit equation is logH/L = -0.0916 logV - 0.041
that can be also expressed as L = 1.1V0.0916 H. The
correlation coefficient is r2 = 0.532 and the standard
deviation is 0.21. The fit proposed by Corominas (1996)
is also presented in the figure. In all these equations, the
volume V is expressed in cubic meters.
Figure 8 shows the relationship between H/L and
volume for rock falls, rock avalanches and volcanic
debris avalanches. Most of the scattered data correspond to rock falls (Corominas 1996). Rock
avalanche data are also scattered, but the largest
ones are concentrated in the lower right part of the
plot and show similar mobility to volcanic debris
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Geotech Geol Eng (2009) 27:23–42
Fig. 7 Relationship
between the apparent
coefficient of friction and
landslide volume—
Comparison between
international (527 events)
and Central American data
(33 events)
avalanches. Volcanic debris avalanches that formed
from sector collapses, as already pointed out by Scott
et al. (2001), behave as large rock avalanches in nonvolcanic environments, but have greater mobility and
the volumes involved are larger. Schuster and Crandell (1984) and later Siebert et al. (1987) proposed
that empirical methods can give a good estimate of
the potential run-out of a debris avalanche if one
assumes that the debris avalanche will have a volume
of at least 1 km3, a value of H/L based on the H/L
ratios of some of the world’s largest debris avalanches, and H is at least as great as the vertical
distance between the top and the base of the volcano
Fig. 8 Comparison of
apparent coefficient of
friction and volume of
Central American rock falls,
rock avalanches and
volcanic debris avalanches
with similar data available
in literature. The analysis
was done with 192 data
available in literature (134
rock fall and rock avalanche
data and 58 volcanic debris
avalanche data) and 18
Central American data (1
rock fall and 17 volcanic
debris avalanches)
123
being considered. Carrasco-Nuñez et al. (1993) suggested that the method only be used for volcanic
debris avalanches that do not transform into debris
flows, and that the anticipated maximum run-out
distance can be calculated by dividing H by 0.04,
which is the minimum H/L found for volcanic debris
avalanches. This approach, in conjunction with an
evaluation of the topography, should lead to a
realistic assessment of the areas most likely to be
affected (Schuster and Crandell 1984).
Figure 9 compares debris flows in volcanic and
non-volcanic environments. Non-volcanic debris
flows include international data from Switzerland,
Geotech Geol Eng (2009) 27:23–42
Canadian Cordillera (Rickenmann 2005), Brazil
(Kanji et al. 2003), and Pyrenees (Corominas 1996).
For volcanic debris flows, the data are more limited,
but the data from Vesuvio volcano (Corominas 1996;
Legros 2002), Cascade Range volcanoes (Vallance
and Scott 1997; Capra et al. 2002) and data presented
in Iverson (1997) are included. Whereas for nonvolcanic debris flows empirical relations are available
(Rickenmann 1999), no specific correlations have
been proposed for volcanic debris flows. This may be
related with the fact that the use of the H/L method
for volcanic debris flows is questionable (CarrascoNuñez et al. 1993; Vallance and Scott 1997; Scott
et al. 2001; Capra et al. 2002) and debris flow run-out
distance could be substantially underestimated by use
of the H/L parameters, especially for cohesive debris
flows. The empirical relationship proposed in earlier
studies for non-volcanic debris flows from the Swiss
Alps (Rickenmann 2005) does not fit with well with
Central American debris flows data.
The data for non-volcanic debris flows from
Switzerland, Canadian Cordillera, Brazil and Pyrenees cover a wide range and seem consistent, while
volcanic debris flows data have large scatter. In terms
of mobility, Brazilian debris flows in weathered
granites (Kanjii et al. 2003) and some debris flows in
the Swiss Alps are the most mobile among the nonvolcanic debris flows. Cohesive volcanic debris flows
from the Cascade Range volcanoes and one in
39
Mexico are the most mobile and show mobility and
volumes comparable to those of volcanic debris
avalanches. The Nicaraguan non-volcanic debris
flows are consistent with the international data.
However, the Central American volcanic debris flows
show values of mobility and volumes more consistent
with international non-volcanic debris flows. Only
the Casita lahar shows values of H/L consistent with
volcanic debris flows presented by Vallance and Scott
(1997).
6.4 Other Relationships
For debris flows, the relationship between the inundation area and flow volume is considered to be a
better indicator of flow mobility than run-out distance
vs. flow volume (Capra et al. 2002; Iverson et al.
1998; Vallance and Scott 1997). However the lack of
inundation area data in the Central American dataset
limited the analysis. In Fig. 10, the available run-out
distance vs. volume data are compared.
7 Summary and Conclusions
A better understanding of the physical characteristics
and behavior of landslides is crucial for realistic hazard
and risk assessment. In this paper a series of empirical
relationships to better describe landslide behavior in
Fig. 9 Comparison of apparent coefficient of friction and volume of Central American non-volcanic and volcanic debris flows (15
events) with similar data available in literature (193 events)
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Geotech Geol Eng (2009) 27:23–42
Fig. 10 Relationship between run-out distance and volume.
The analysis was done with 296 data available in literature
(134 rock fall and rock avalanche data, 58 volcanic debris
avalanche data, 67 debris flows and debris avalanches, 37
volcanic debris flows) and 33 Central American data
Nicaragua and in its neighbouring countries of El
Salvador, Costa Rica and Guatemala, were proposed.
Based on the available field data, different types of
landslides were studied, but the focus of the study was
on debris flow behavior. The relationships among the
important parameters characterizing landslides, such
as run-out distance, landslide volume, height of fall and
run-out ratio were studied, and a series of empirical
relations emerged.
The analyzed data show differences in run-out
distance and landslide mobility among different types
of landslides and between debris flows in volcanic and
non-volcanic areas. For rock falls and slides the
relationship between run-out and height of fall is
approximately linear. For volcanic debris flows the
run-out distance increases proportionally to the height
of fall up to a run-out distance of about four kilometres,
but larger run-outs seem to be independent of the height
of fall. Volcanic debris flows that occur on volcano
slopes (conical shape) reach longer distances than
those in the inner walls of calderas and craters and in
non-volcanic areas because of different slope geometry, slope inclination and topographic constraints.
Besides the landslide volume, geotechnical material
properties also affect the run-out distance. However,
the lack of reported data on material properties does not
allow the authors to quantify the influence.
The height of fall alone is not sufficient parameter
for predicting the run-out distance, because for the
same height of fall, different values of H/L (i.e.
mobility) can be found especially in non-volcanic
areas. The empirical relations obtained for events in
Central America are largely consistent with those
proposed in the literature for other regions. In general,
the tendency for the apparent friction coefficient to
decrease with landslide volume is in line with earlier
investigations. Crosta et al. (2005) emphasized that
landslides in volcanic materials are usually characterized by a higher mobility than those involving nonvolcanic rocks. The Central American data also show
clearly that volcanic debris avalanches have higher
mobility than other types of landslides. Because of
scattered volcanic debris flow data is difficult to
compare the Central American volcanic debris flows
with similar events in other countries. It is observed
that volcanic debris flows that transformed from
volcanic debris avalanches show higher volume and
mobility with respect to the non-volcanic debris flows
and the volcanic debris flows that started as water
floods and transform into debris flows by incorporating
sediment through erosion. The 1998 Casita debris flow
that transformed from a debris avalanche shows a value
of H/L of about 0.11. Other Central American volcanic
debris flows that started as water floods and transformed into debris flows by incorporating sediment
through erosion show volume and mobility values
more consistent with the most mobile and largest
international non-volcanic debris flows.
123
Geotech Geol Eng (2009) 27:23–42
The study also highlighted the shortcomings of the
Nicaraguan database. The analysis showed that there
is a scarcity of reliable data, and demonstrated the
necessity of collecting more quantitative and qualitative information in the field. During a landslide
survey, one should obtain estimates of volume, runout distance, inundation area, and the height difference of the landslide deposit. More sophisticated
parameters, such as the geometrical shift of the center
of mass of the landslide, should preferably also be
estimated and recorded. More quantitatively oriented
databases will increase our understanding of the
mechanical, dynamic, and rheological characteristics
of landslides. This, in turn, will improve future
hazard zoning and design of optimal risk mitigation
measures.
Acknowledgements The work presented in this paper was
supported by the Research Council of Norway through the
Centre of Excellence ‘‘International Centre for Geohazards’’
(ICG ). Their support is gratefully acknowledged. The authors
also wish to thank José Cepeda, who provided data from El
Salvador, and Carolina Sigarán and Guillermo Alvarado who
provided data from Costa Rica. Dr. Farrokh Nadim provided
very useful comments and suggestions in reviewing the
manuscript.
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