I NSIVUMEH 

Landslides Triggered by Hurricane Mitch in Guatemala— 

Inventory and Discussion 

by Robert C. Bucknam, Jeffrey A. Coe, Manuel Mota Chavarría, Jonathan W. Godt, Arthur C. Tarr, 

Lee-Ann Bradley, Sharon Rafferty, Dean Hancock, Richard L. Dart, and Margo L. Johnson 

Open-File Report 01-443 

(also available in Spanish) 

2001 

U.S. Department of the Interior 

U.S. Geological Survey 
I NSIVUMEH 

Landslides Triggered by Hurricane Mitch in Guatemala— 

Inventory and Discussion 

by Robert C. Bucknam,1 Jeffrey A. Coe,1 Manuel Mota Chavarría,2 Jonathan W. Godt,1 Arthur C. Tarr,

1 

Lee-Ann Bradley,

1 Sharon Rafferty,1 Dean Hancock, Richard L. Dart1 and Margo L. Johnson1 

This report is based on a cooperative study by the U.S. Geological Survey, Denver, Colorado and the Instituto 

Nacional de Sismologia, Vulcanologia, Meteorologia e Hidrologia, Guatemala City, Guatemala. Work funded by 

the U.S. Agency for International Development’s Hurricane Mitch Reconstruction Program. 

Open-File Report 01-443 

(also available in Spanish) 

Cover Photos: Hurricane Mitch approaching Honduras on 1998 October 26, 13:15 

UTC (October 26, 07:15 local time). Note band of rain clouds in eastern Guatemala 

(outlined in yellow) about 650 km in front of the eye of the hurricane. The image is 

derived from satellite data which has been color-enhanced and processed to yield a 

perspective rendering of the hurricane. Modified from image produced by Hal Pierce, 

Laboratory for Atmospheres, NASA Goddard Space Flight Center. 

Landslide triggered by Hurricane Mitch on November 1, 1998, Rio La Lima, Sierra de 

las Minas, Guatemala. Photograph by Jeffrey Coe, January 2001. 

1USGS, Denver, Colorado


2INSIVUMEH, Guatemala City, Guatemala


This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial 

standards nor with the North American Stratigraphic Code. Any use of trade names in this publication is 

for descriptive purposes only and does not imply endorsement by the U.S. Government. 

2001 

U.S. Department of the Interior 

U.S. Geological Survey 
ABSTRACT 

The torrential rains that accompanied 

Hurricane Mitch in October and November 

of 1998 triggered thousands of landslides in 

the moderate to steep terrain bordering the 

Motagua and Polochic Rivers in eastern 

Guatemala. Using aerial photographs taken 

between January and March 2000 we 

mapped all visible landslides larger than 

about 15 m in minimum dimension in a 

study area of 10,000 km2 encompassing 

twenty 1:50,000-scale topographic map 

quadrangles. 

Rainfall from Hurricane Mitch was 

exceptional because it was geographically 

widespread, prolonged over a period of 

about a week, moderate to heavy in intensity, and occurred at the end of the rainy season when the ground already had a high 

moisture content. As documented in this 

report, this type of rainfall, on saturated or 

nearly saturated ground, has the capability to 

trigger both shallow and deep-seated landslides over a large area. 

We mapped about 11,500 landslides in 

the study area. The mapped landslides were 

of two general types: relatively small, translational and rotational landslides that commonly mobilized into debris flows and covered less than several hectares in area (not 

including flow paths), and large, commonly 

translational, landslides that sometimes generated debris flows and covered between 

15 ha and 25 ha (not including flow paths). 

The main concentrations of landslides are on 

moderate-to-steep hillslopes underlain by 

diverse geologic units. For the purpose of 

describing the mapped landslides, we divided the study area into five distinct regions 

based on differing geologic and geomorphic 

characteristics. These regions include the 

upper Polochic valley and surrounding highlands, the central Sierra de las Minas, the 

hills surrounding La Union and Zacapa, the 

eastern Sierra de las Minas, and the border 

region with Honduras. All of these areas 

received between 200 mm and 600 mm of 

rain over a 13-day period between October 

25 and November 6. The highest rainfall 

amounts (400 mm to 600 mm) occurred in 

the Upper Polochic valley and surrounding 

highlands and in the central Sierra de las 

Minas. The lower rainfall amounts (200 mm 

to 400 mm) occurred in the hills surrounding La Union, the eastern Sierra de las 

Minas, and in the border region with 

Honduras. In general, the rainfall received in 

these areas is roughly equivalent to the average precipitation received in a 1-year period. 

We used 10-m digital elevation models 

(DEMs) generated from contours on two 

quadrangles in the central Sierra de las 

Minas to create a map showing areas that 

were susceptible to landslides during 

Hurricane Mitch. To create the Hurricane 

Mitch susceptibility map, we developed a 

susceptibility threshold equation based on 

elevation and gradient. The analysis indicates that, at least on two quadrangles, gradients less than 9o were not susceptible to 

landslides during Hurricane Mitch. The 

slope of the line defined by the threshold 

equation indicates that less rainfall was 

required to initiate landslides on steep gradients than on shallow gradients. Ninety percent of the mapped landslides that were triggered by Hurricane Mitch are within the 

susceptible zone shown on the map. Eightysix percent of landslides that were mapped 

as predating Hurricane Mitch, and all landslides mapped as postdating Hurricane 

Mitch, are within the susceptible zone. 

We used LAHARZ software to model the 

potential downstream area affected by debris 

if a large landslide dam on the Río La Lima 

were to fail. The model shows that the area 

affected would be similar to the area that 

was affected by a debris flow that mobilized 

from a large landslide along the Río La 

Lima during Hurricane Mitch. 

The characteristics of rainfall-triggered 

landslides described in this report can be 

used as a partial guide to future landslide 

activity triggered by rainstorms. On the 

basis of existing data, hazardous areas 

include: moderate to steep hillslopes and 

less steep areas directly below these hillslopes, drainage channels downslope from 

landslide prone hillslopes, and alluvial fans 

at the mouths of drainages along mountain 

or hillslope fronts. Evidence for, and frequency of, past landslides at individual sites 

can be used to determine the level of future 

hazard. That is, one of the best indicators 

1
for future landslide activity is evidence of 

past landslide activity. For this reason, landslide inventory maps showing Quaternary, 

historic, and modern landslides are of critical importance and should continue to be 

compiled. 

Useful tools for predicting the occurrence 

of rainfall-triggered landslides in populated 

areas are rainfall intensity/duration thresholds. New and existing rainfall and landslide 

data could be used to develop two thresholds for Guatemala, one for debris flows 

triggered by intense bursts of rainfall, and 

one for deep-seated landslides triggered by 

prolonged rainfall. 

INTRODUCTION 

Hurricane Mitch, one of the strongest 

Atlantic hurricanes in history, began as a 

tropical depression in the western Caribbean 

Sea on October 22, 1998, and became a hurricane 2 days later several hundred kilometers south-southwest of Jamaica. The hurricane intensified rapidly, and by the 26th it 

was a category 5 hurricane with maximum 

sustained surface wind speeds estimated at 

290 km per hr and gusts over 320 km per 

hour (Lott and others, 1999). By October 27, 

Hurricane Mitch began to weaken and made 

landfall on the north coast of Honduras on 

the morning of October 29, but widespread 

heavy rainfall in advance of the eye of the 

hurricane (fig. 1) had already caused extensive damage in Honduras, Nicaragua, 

Guatemala, and El Salvador from flooding 

and landsliding. By October 30, Hurricane 

Mitch had weakened to a tropical storm, and 

by the next day it had become a tropical 

depression (Guiney and Lawrence, 1998). 

Rainfall from Hurricane Mitch affected 

southern Guatemala between October 27 and 

November 1st (fig. 2). Surface circulation 

from the storm dissipated near the 

Guatemala/Mexico border on November 1, 

but locally heavy rain continued over 

Central America for the next several days 

(Guiney and Lawrence, 1998). 

Measurements of the amounts of rain that 

fell during the storm were sparse, particularly at high elevations in mountainous regions 

where rain gages typically were absent and 

orographic effects are likely to have 

enhanced the amount of rainfall. However, 

Figure 1. Track of Hurricane Mitch through the western Caribbean and Central America, October 26 to November 1, 1998 

(coordinates from National Hurricane Center). Large red circles show locations of low pressure eye of the hurricane at date 

and time indicated; times (Z) are Universal Time Coordinated. Yellow polygon is area of this study. 

2
6 

5 

9 

1 

3 

4 

7 

8 

2 

A Figure 2A. Distribution of Hurricane 

Mitch rainfall in Guatemala at stations in 

the regional meteorological network of 

INSIVUMEH (open circles with crosses) 

for the period October 25–November 6, 

1998, and San Lorenzo station of INDE 

(solid circle with cross). Numbers by symbols refer to stations shown in figure 2B. 

B 

B. Cumulative precipitation at meteorological stations of INSIVUMEH and INDE in and adjacent to the landslide-inventory study area for the period October 25–November 6, 1998. 

3
records from regional networks in Central 

America show rainfall amounts from the 

storm as high as 1,612 mm, recorded 

between October 21 and 31, in westernmost 

Nicaragua near the Pacific coast (Instituto 

Nicaragüense de Estudios Territoriales, 

1998). Hellin and Haigh (1999) report 

896 mm between October 27 and 31 from a 

station in southern Honduras, and in 

Guatemala, the Puerto San José station on 

the Pacific Coast recorded 1,069 mm 

between October 25 and November 1, 1998 

(fig. 2). Heavy rain in eastern Guatemala 

began about October 27 in association with 

bands of rain 650 km in advance of the eye 

of the hurricane (see report cover). Rainfall 

in Guatemala was highly variable; between 

October 25 and November 6, 1,069 mm was 

recorded at Puerto San Jose on the Pacific 

coast, 663 mm was recorded at a high mountain site in the Sierra de las Minas, and 

182 mm was recorded in the Motagua Valley 

(fig. 2). 

Guatemala Impacts 

The intense rains of Hurricane Mitch produced landslides and flooding in Guatemala 

that caused extensive damage to infrastructure, and, despite preventive evacuation of 

more than 100,000 people at high risk, an 

estimated 268 fatalities occurred (U.S. 

Agency for International Development, 

1999). Damage to infrastructure included 53 

bridges damaged and 68 destroyed, 90 sections of road affected, and 2,293 houses 

were destroyed and 19,332 damaged. There 

was extensive damage to productive agricultural areas and farm-to-market access roads 

and trails. Agriculture was heavily impacted, 

with 90,000 hectares (ha) of losses in basic 

grains, coffee, vegetables, and bananas. 

Facilities for small production coffee processing were also seriously affected. The 

Government of Guatemala and the United 

Nations estimated rehabilitation and reconstruction costs at US$550 million. 

Much of the landslide damage to agriculture and roads was in the steep terrain bordering the Motagua and Polochic Rivers. 

However, even months after the hurricane, 

little was known or documented about the 

nature and distribution of the landslides, and 

many areas remain exposed to landslides 

from future periods of sustained heavy rainfall. Under the U.S. Agency for 

International Development (USAID) 

Hurricane Mitch Reconstruction Program, 

the U.S. Geological Survey (USGS) in collaboration with Instituto Nacional de 

Sismologia, Vulcanologia, Meteorologia e 

Hidrologia (INSIVUMEH) undertook the 

development of a comprehensive inventory 

of landslides by moderate-scale mapping of 

a large area (20, 1:50,000-scale quadrangles) 

adjacent to the Motagua and Polochic Rivers 

(fig. 3). These maps provide a detailed 

record of landslides over a large geographic 

area (about 10,000 km2) of diverse geology, 

geomorphology, microclimates, and vegetation. If combined with data on the physical 

properties of hillslope materials, hillslope 

form, and rainfall characteristics, these maps 

can provide a foundation for evaluating the 

susceptibility of other similar areas to landsliding. 

Geologic and Geographic Setting 

The study area encompasses the steep 

mountainous terrain that borders the 

Motagua and Polochic Rivers in east-central 

Guatemala (fig. 3). The east-northeasttrending Sierra de las Minas, which lies 

between the two rivers, rises from an elevation of about 10 m at the Polochic River and 

200 m at the Motagua River to an elevation 

of 2,948 m at the crest of the range south of 

the Polochic River. To the north of the 

Polochic River, the terrain rises more than 

1,800 m to a high north-sloping karst 

plateau with scattered peaks at elevations up 

to 2,540 m. 

The Polochic and Motagua Rivers follow 

the general trend of the Motagua and 

Polochic fault systems, two sub-parallel leftlateral faults that mark the boundary 

between the North American plate to the 

north and the Caribbean plate to the south. 

Paleozoic metamorphic rocks are the predominant rock type in the central part of the 

Sierra de las Minas range; clastic and carbonate rocks are the dominant rock types at 

the eastern end of the range (Bonis and others, 1970). 

4
Figure 3. Index map 

to landslide-inventory 

mapping area. 

Population centers and highways are concentrated in the Motagua and Polochic valleys. The two most important highways in 

the region are CA9 in the Motagua valley 

and 7E in the Polochic valley. These two 

east-west-trending roads link population 

centers and agricultural areas with Puerto 

Barrios, the primary port city on the 

Caribbean Sea. Both of these roads were 

closed by landslides during Hurricane 

Mitch, and Highway CA9 was closed again 

by a debris flow in 1999. Secondary roads 

and farm trails on the flanks of the ranges 

bordering the Motagua and Polochic Rivers 

are important routes for communication with 

small communities and for transport of agricultural products. Landslides triggered by 

Mitch cut many of these routes. 

General Landslide Terminology 

We use the term “landslide” to describe 

all types of gravitational slope failures: 

rotational and translational slides, slowmoving earth flows, (Varnes, 1978; Cruden 

and Varnes, 1996), and fast-moving debris 

flows composed of mud, gravel (up to 

boulder-sized material) and organic debris 

that often mobilize from slides (see Pierson 

and Costa, 1987, for classification of fastmoving flows). Most of the landslides that 

we mapped are debris flows. Debris flows 

typically occur in response to periods of 

intense rainfall. They initiate as rotational or 

translational slides that turn into muddy 

slurries, or from concentrated erosion of 

surface material by runoff. As they travel 

down hillslopes and channels, the slurries 

can substantially increase in volume by 

incorporating additional colluvium, channel5
The aerial photographs 

used in this study are 

available from: 

U.S. Geological Survey 

EROS Data Center 

Attn: Ron Risty 

47914 252 Street 

Sioux Falls, SD 57198 

Telephone: 

605 594-6969 

E-mail: risty@usgs.gov 

http://mitchnts1.cr.usgs. 

gov/data/aerial.html 

fill material, and water. Addition of sufficient volumes of water relative to the sediment content can also result in dilution of 

the debris flow to the consistency of normal 

streamflow. Debris flows can occur with little warning and are capable of transporting 

coarse debris (containing fragments 5 m or 

more in longest dimension) long distances 

over relatively gentle slope gradients. Debris 

flows can develop momentum as well as 

impact forces that can cause considerable 

destruction. As a result of these characteristics, reducing the hazards of debris flows 

can be more difficult than those of floods. 

METHODS 

Digital versions of 1:50,000-scale topographic maps of Guatemala were used as 

base maps for photogrammetric compilation 

and presentation of the landslide data. 

Digital data for most quadrangles were provided by the National Imaging and Mapping 

Agency (NIMA), which digitally scanned 

published topographic maps, converted the 

scanned images to equirectangular projection (a non-conformable projection; see 

Snyder, 1987), and combined the images 

into mosaics that were supplied to the 

USGS. Digital versions of a few quadrangles 

for which there were newer base maps than 

those supplied by NIMA were prepared by 

the USGS or a commercial vendor by scanning the most recent published versions of 

the quadrangles and georeferencing the 

scanned images to the same projections and 

datums as the published maps. 

Landslide inventory maps are based on 

interpretation of 1:40,000-scale black-andwhite aerial photographs taken between 

January 14 and March 6, 2000. The area for 

which aerial photographs were requested for 

mapping was based on a reconnaissance helicopter survey of the region in September 

1999 by the USGS and INSIVUMEH. The 

aerial photographs were taken as part of a 

cooperative map revision project by Instituto 

Geografico Nacional (IGN) and NIMA. 

Cloud cover on the photographs was minor 

except for a few photographs on which 

clouds covered as much as about 40 percent 

of the image. Where the ground was 

obscured by clouds, the approximate outline 

of the covered area is shown on the maps. 

In areas where the concentration of landslides was moderate to high, a Kern PG-2 

photogrammetric plotter was used to map 

the landslides. The PG-2 plotter is traditionally used to create topographic maps, but 

also has many geologic applications 

(Pillmore, 1989). The plotter is a highresolution optical-mechanical instrument 

that makes it possible to stereoscopically 

view aerial photographs at 2x, 4x, or 8x 

magnification. The plotter has an illuminated marker that is mechanically linked to a 

pencil mounted on an arm above a base 

map. Photographs in the PG-2 are registered 

to a base map using prominent topographic 

or cultural landmarks. Once registered, features visible in the photographs can be 

drawn on the base map by tracing the features on the map while stereoscopically 

observing the illuminated marker on the 

photographs. 

We mapped the landslides from the 

1:40,000 scale photographs on transparent 

polyester overlays registered to 1:50,000- or 

1:25,000-scale (2x enlargements of the base 

maps). The photographs were taken between 

January and March 2000; thus all mapped 

landslides occurred prior to this date. The 

scale of the photography allowed us to accurately identify and map landslide features as 

small as about 15 m in width. Each landslide shown on the maps includes a headscarp, downslope travel path, and the resulting deposits. Landslides were mapped as 

Hurricane Mitch-caused if features appeared 

to be fresh, that is, non-vegetated. Hurricane 

Mitch landslides typically appear as nearly 

white scars that contrast strongly with the 

adjacent darker vegetated ground surface. 

Landslides that were significantly darker in 

tone or that appeared to have some vegetation, but still appeared to be relatively fresh, 

were mapped as pre-Hurricane Mitch landslides. In one instance, on the Río Hondo 

quadrangle (plate 9), we mapped a group of 

landslides as post-Mitch because a large 

debris flow in the drainage below the landslides closed a major highway on September 

17, 1999, nearly a year after Hurricane 

Mitch. In some quadrangles, we also 

mapped fresh flood deposits along major 

6
rivers and tributary drainages. In general, 

the downstream extent of debris-flow 

deposits was not known, and the storm 

effects mapped in tributary stream channels 

are likely a mixture of debris-flow deposits, 

channel scour, and flood deposits. 

In areas where the concentration of landslides was sparse, it was more time efficient 

to use a desktop mirror stereoscope to map 

the landslides. Using the stereoscope, photographs were viewed stereoscopically at 3x 

magnification. Outlines of landslides were 

transferred from the photographs to the base 

maps by visual inspection; that is, we identified the landslide on the photographs, found 

the location of the landslide on the map, and 

manually drew the outline of the landslide 

on the map. As with the photogrammetric 

plotter mapping, we mapped from 1:40,000 

scale photographs onto 1:50,000 or 1:25,000 

scale base maps onto transparent overlays. 

In general, only Hurricane Mitch landslides 

and flood deposits (as defined above) were 

mapped with the mirror stereoscope. 

Accuracy 

Accuracy of the mapped landslides is 

comparable to the accuracy of the 1:50,000-

scale topographic maps used as base maps. 

When scaling the photogrammetric model to 

the topographic maps, we found that some 

features, such as the courses of some 

streams, were generalized or simplified on 

the maps. Because digital versions of our 

landslide maps could in the future be transferred to a revised and possibly more accurate base map, we did not modify our mapping to match local deviations from the 

topographic base maps. 

A conspicuous example of inaccuracy in 

a base map is shown on the Juyama quadrangle (plate 18) at UTM 294,400 m E, 

1,684,600 m N. What is shown on the base 

map as a single stream is actually two 

streams separated by a narrow drainage 

divide. A landslide and its downstream 

deposits that appear to climb uphill out of a 

drainage actually stay within a parallel side 

drainage that is not shown on the base map. 

The maps accurately portray the shape, 

size, and relative location of landslides and 

related downslope channel deposits. 

However, in some locations mapped channel 

deposits are not well aligned with the 

drainages as shown on the base maps. This 

may be due to: 

(1) differences between generalized 

depiction of drainages on the base maps 

and detailed mapping of landslide channel deposits (as described above), 

(2) changes in the courses of streams 

since the time that the base maps were 

made, 

(3) locally insufficient topographic control to accurately register the aerial photographs to the base maps, and 

(4) better exposure of the courses of 

drainages in some heavily vegetated areas 

by clearing of trees since the base maps 

were prepared. 

Considering all these potential mapping 

errors, we estimate that landslide locations 

mapped using the PG-2 plotter are typically 

accurate to within 50-100 m. The locations 

of landslides that were mapped using a mirror stereoscope are estimated to be accurate 

to within approximately 200 m. 

Digital Data Processing 

The digital data that comprise each map 

are publicly available as ArcInfo Export data 

files. Links to the files are given at 

http://mitchnts1.cr.usgs.gov/data/landslide.html. 

Each map may have up to four data layers 

associated with it in addition to the layer 

depicting the landslides triggered by 

Hurricane Mitch. The additional data include 

(1) clouds in the aerial photographs that 

obscured the ground surface, (2) the limit 

and method of mapping, (3) landslides interpreted as having occurred prior to Hurricane 

Mitch, (4) landslides that occurred after 

Hurricane Mitch in September of 1999, and 

(5) landslide initiation locations. Landslide 

initiation locations are points that were digitized at the upslope end of each landslide 

polygon. These points are assumed to be 

landslide initiation locations and are called 

such throughout the report. Each data file 

has an alphanumeric file name. The two 

7
--

--

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

characters that begin the file name indicate 

which features the file contains (see table 1), 

and the five digit numeric code corresponds 

to one of the 20 quadrangles (see table 2). 

For example, the file named ls22612.e00 

contains the landslides triggered by 

Hurricane Mitch (‘ls’) for the Rio Hondo 

quadrangle (‘22612’). The suffix (‘.e00’) 

identifies it as an ArcInfo Export file. 

The mapped features were converted to 

digital vector data in an ArcInfo Geographic 

Information System (GIS) by either manual 

digitization or optical scanning. These data 

were clipped at the quadrangle boundary and 

manually edited to build topology and in a 

few cases to correct location errors. 

Landslide features are represented as polygons and carry a single attribute (LS) indicating whether the feature is a landslide 

(attribute = 1) or an area within a landslide 

polygon that appeared unaffected (attribute = 

0, see table 1). The mapping method and 

limits are represented by polygons that carry 

a single attribute (MM) indicating either that 

Table 1. Information regarding ArcInfo data files available at


http://mitchnts1.cr.usgs.gov/data/landslide.html. 


Individual columns are described in the text.


File identifier Feature type Attribute Value 

‘ls’ Landslide triggered by 

Hurricane Mitch 

‘ols’ Old landslide feature LS 0 or 1 

‘yls’ Landslide that occurred after 

LS 0 or 1 

LS 0 or 1 

Hurricane Mitch 

‘ip’ Landslide initiation location


‘cl’ Clouds


‘mm’ Mapping method and limit MM mirror, plotter,


unmapped 

Table 2. Index linking quadrangle names and plate numbers to digital file codes. 

Quadrangle name Plate number Numeric code Available files 

Cobán 21623 

Tactic 21614 

Caquipec 21622 

Tucurú 21611 

Senahú 22623 

La Tinta 22614 

Panzós 22622 

Pueblo Viejo 22611 

Río Hondo 22612 

Zacapa 22601 

Sierra de las Minas 23614 

Gualán 23613 

La Unión 23604 

Mariscos 23622 

Los Amates 23611 

Castillo San Felipe 24624 

Morales 24623 

Juyamá 24614 

Entre Ríos 24621 

Cerro Caral 24622 

‘ls, ols, ip, mm’


‘ls, ols, ip, mm’


‘ls, ip, mm’


‘ls, ip’


‘ls, ols, ip, cl, mm’


‘ls, ols, ip’


‘ls, ols, ip, mm’


‘ls, ols, ip, cl, mm’


‘ls, ols, yls, ip’


‘ls, ip, mm’


‘ls, ols, ip, cl, mm’


‘ls, ip, mm’


‘ls, ols, ip, mm’


‘ls, ip’


‘ls, ip, cl, mm’


‘ls, ols, ip, mm’


‘ls, ip’


‘ls, ip, cl, mm’


‘ls, ols, ip, mm’


‘ls, ip, cl, mm’


8
the landslide features within the polygon 

were mapped with a photogrammetric stereoplotter ( = plotter) or a mirror stereoscope 

(= mirror). If the limit of the study area falls 

within a quadrangle, the polygon defining 

the unmapped part is attributed as MM = 

unmapped. 

To prepare the maps, the digital vector 

data were assembled in ArcMap 8.1 running 

on a Windows workstation and exported as 

Encapsulated Postscript (eps) files. The map 

base for each sheet is an optically scanned 

image of the published 1:50,000-scale paper 

map that was georeferenced to the map 

coordinates of each quadrangle. A georeferenced image maintains a relation between 

the image pixels and planar-map page coordinates. The base map images were color 

corrected and sharpened using Adobe 

Photoshop 6.0 running on a Windows workstation. The final map graphics were assembled in Adobe Illustrator 9.0 running under 

MacOS 9.0 and are available online as 

Adobe Portable Document (.pdf) files. 

Resolution at map scale 

The 1:50,000 scale of the base maps limits the resolution of our mapping. For example, using a carefully sharpened lead in the 

photogrammetric plotter to map the outline 

of the landslides produces a line about 

0.1 mm wide, and as the lead wears, the line 

commonly increases to 0.2–0.3 mm width. 

At a line width of 0.3 mm, features less than 

about 15 m across cannot be shown without 

exaggeration, and this represents the typical 

lower limit of the size of features shown on 

the maps. 

Field observations 

We conducted several reconnaissance 

field reviews (both air and ground based) of 

our aerial photographic mapping. The purpose of the field observations was to provide 

comparisons between the characteristics of 

landslides observed on aerial photographs 

and their characteristics as observed at low 

levels from the air and on the ground, to 

verify the completeness and interpretations 

of the mapping, to obtain measurements on 

materials and other characteristics that cannot be obtained from aerial photographs, 

and to obtain eyewitness accounts of landslide events. Ground-based field observations were limited to about a dozen remote 

landslide sites that had suitable landing 

areas for a helicopter and sites that had 

nearby access by road or jeep track. 

Completeness 

In the areas that we have investigated, we 

estimate that the maps show greater than 

95 percent of all landslides larger than about 

15 m in smallest dimension except on very 

steep hillslopes or in heavily forested areas. 

On very steep hillslopes, the angle of view 

near the margins of the aerial photographs 

can be nearly parallel to the ground surface, 

and landslides in those cases may not be 

visible on the photographs. In densely 

forested areas, small landslides may be 

obscured by the forest canopy, and the ability to see larger landslides is a complex relationship between the geometry of the aerial 

photograph, the height and density of the 

forest canopy, and the direction and amount 

of slope gradient of the ground surface. At 

the principal point (center) of a 1:24,000-

scale aerial photograph, Pyles and Froehlich 

(1987) calculated that a landslide would 

need to be 30 m on a side (1 ha) to be visible. At the edge of the photograph, a landslide on a 39° (80 percent) hillslope facing 

away from the principal point would need to 

be 100 m on a side (1 ha) to be equally visible. Pyles and Froehlich’s (1987) study 

showed that without knowledge of the true 

density of landslides in heavily forested 

areas our maps of landslides cannot be used 

to draw inferences about the impact of 

clearing of forests on landslide occurrence 

from Hurricane Mitch, or by extension, 

other similar heavy rainfall events. 

PRECIPITATION 

Intense and/or prolonged rainfall is a 

principal trigger for debris flows and landslides. Studies in temperate and humidtropical environments have shown that there 

is a threshold in the relationship between 

rainfall intensity and duration for stormrainfall-triggered landslides (Caine, 1980; 

Cannon, 1988; Larsen and Simon, 1993). 

High-intensity, short-duration rainfall events 

9
typically trigger shallow soil slips and debris 

flows. Long-duration, low-intensity rainfall 

typically produces large deep-seated landslides, such as debris avalanches and slumps 

(Larsen and Simon, 1993). In Guatemala, 

Hurricane Mitch produced landslides typical 

of both high-intensity short-duration and 

long-duration low-intensity rainfall. Small 

landslides mapped in this study are likely 

the result of local severe storm cells that 

formed during the passage of Mitch, whereas the large deep-seated landslides were the 

result of the prolonged rain during the 

approximately 6-day passage of Mitch 

through Guatemala. 

General Characteristics of 

Precipitation in Guatemala 

The study area encompasses a wide range 

of rainfall, most of which falls in the wet 

season from May through October, when the 

area receives 80–90 percent of its annual 

precipitation (Portig, 1976). A regional rainfall map of Central America shows annual 

totals in the general area of this study as 

ranging from less than 100 mm/yr in the low 

elevations along and south of the Motagua 

River west of Zacapa (fig. 3), and 200–300 

mm/yr in the eastern part of the study area 

(Portig, 1976), to more than an estimated 

600 mm/yr in the Sierra de las Minas north 

of the Polochic River. Data for the Sierra de 

las Minas were lacking in Portig’s (1976) 

study, and orographic effects may result in 

annual total rainfall higher than he estimated. However, the relationship between elevation and precipitation is likely to be complex. For example, in Costa Rica, large rainfall totals have been found to be concentrated on the tops of mountains of moderate elevation and on the slopes of the high ranges. 

Range crests above about 2,500 m receive 

less than half the precipitation of that on the 

slopes (Portig, 1976). 

Rainfall During Hurricane Mitch 

Local heavy storms during the rainy season in Guatemala periodically trigger landslides each year, but the duration and widespread nature of heavy rains from Hurricane 

Mitch provided the conditions needed to 

produce landslides over a wide area. 

Additionally, Hurricane Mitch struck 

Guatemala at the end of the rainy season 

when antecedent soil moisture levels were 

high. Meteorological stations, which are 

widely but sparsely distributed across 

Guatemala, provided a general picture of the 

precipitation associated with Hurricane 

Mitch throughout the country, which ranged 

from 182 mm to 1,069 mm (fig. 2). Two stations, San Lorenzo and Pasabien (fig. 2), 

provided data adjacent to the core area of 

dense landslides in an area of high relief— 

the Sierra de las Minas—which was heavily 

impacted by landslides and debris flows 

from Hurricane Mitch. Station San Lorenzo, 

operated by Instituto Nacional de 

Electrificación (INDE), is on the south flank 

of the Sierra de las Minas at an elevation of 

1,780 m. The crest of the range lies 9.5 km 

northwest of the station at an elevation of 

2,987 m. Station Pasabien, operated by 

INSIVUMEH, is at the base of the range at 

an elevation of 250 m, 6 km south of Station 

San Lorenzo. 

Data from the San Lorenzo and Pasabien 

gages indicate that rainfall during Mitch was 

prolonged and moderate to heavy, but not 

extraordinary during any single day. At 

Station San Lorenzo, which was at an elevation comparable to that where abundant 

landslides occurred in the surrounding area, 

there were 4 consecutive days each with 

more than 40 mm of rain (figs. 4A and 5). 

Maximum daily rainfall was 65 mm on 

October 30. Total cumulative rainfall during 

Mitch (October 27–November 1) was 

275 mm (figs. 4A and 5). At Station 

Pasabien, at an elevation where debris flows 

were absent on nearby surrounding hillslopes (plate 9), there were only 2 consecutive days with rainfall above 20 mm (figs. 

4B and 5). Maximum daily rainfall was 

60 mm on October 31. Total cumulative 

rainfall at station Pasabien (October 27– 

November 1) was 124.5 mm. 

Cumulative rainfall amounts at the two 

stations during the 1998 rainy season were 

quite different. At Station San Lorenzo , 

cumulative rainfall prior to Mitch (March 1– 

October 22, 1998) was 1,082 mm (fig. 5). 

Daily rainfall on 2 days during this period 

(67 mm on June 1 and 71 mm on September 

6) was greater than rainfall on any day dur10
ing Mitch, but did not trigger any reported 

debris flows. This indicates that, either 

antecedent soil moisture on these dates was 

less than adequate to trigger debris flows, or 

that the rainfall was too short in duration to 

trigger debris flows. At the nearby Station 

Pasabien, 1,530 m lower in elevation, cumulative rainfall during the same period prior to 

Mitch was 573 mm (fig. 5). Both cumulative 

seasonal rainfall and rainfall during 

Hurricane Mitch at the two sites show that 

elevation has a strong influence on precipitation. 

Rainfall in 1999 (Quebrada Sucia event) 

On September 17, 1999, debris flows in 

the Quebrada Sucia drainage on the Río 

Hondo quadrangle (plate 9) closed Highway 

CA9. The event is described in detail in a 

later section of this report. Rainfall associated with this event is shown in figures 6 

and 7. The San Lorenzo gage is about 

3 km west of the source area for the 

debris flows and at a similar elevation, 

whereas the Pasabien gage is about 6 km 

to the southwest and at a lower elevation. 

Both gages show that 1999 was a wet 

year (figs. 6 and 7). Annual rainfall prior 

to September 17 at the San Lorenzo gage 

was about 1,280 mm, which is about 

200 mm more than 1998 annual rainfall 

prior to Mitch. Rainfall on September 17 

at the San Lorenzo gage was about 

66 mm, which is about the same as the 

heaviest daily rainfall at the gage during 

Mitch (65 mm). Data from the San 

Lorenzo gage also indicate that the 

debris flows occurred in about the middle of the most intense, 2-week period of 

rainfall in 1999. 

Overview of Landslide Variability and 

Distribution within Study Area 

We mapped about 11,500 landslides 

in the study area (plates 1-21). In a broad 

sense, the mapped landslides were of 

two general types: relatively small, translational and rotational landslides that 

commonly mobilized into debris flows 

and covered less than several hectares in 

area (not including flow paths), and 

large, commonly translational, landslides 

that sometimes generated debris flows 

and covered between 15 ha and 25 ha in 

area (not including flow paths). The 

majority of landslides mapped were the 

Figure 4. Precipitation during 1998 in the Sierra de las Minas at rain gage first type. The small landslides were 

stations San Lorenzo (A) and Pasabien (B). Station elevations in upper left probably triggered during intense bursts 

corner of figures; daily precipitation during heavy rain of Mitch at the stations of rainfall between October 27 and 

(October 27–November 1) shown by filled red bars. November 1. For some large landslides, 

RESULTS


11
Figure 5. 

Cumulative precipitation in the Sierra 

de las Minas at rain 

gage stations San 

Lorenzo and 

Pasabien during 

Hurricane Mitch. 

Station elevations 

given in the inset; 

date and elevation of 

landslide initiation 

location for two 

large landslides on 

the Río la Lima 

given in insets. 

we were able to collect detailed time-ofoccurrence information from eyewitnesses. 

Where we have these data, there is a 

remarkable coincidence in the documented 

dates of occurrence; they all occurred on 

November 1. The upper Río Lima landslide 

in the Río Hondo quadrangle (plate 9) was 

one of the large landslides with a documented time of occurrence. The rain gage located 

near this landslide (the San Lorenzo gage) 

indicates that 275 mm of rain fell over the 6-

day period before the landslide occurred 

(fig. 5). If we assume that antecedent moisture conditions necessary for the occurrence 

of landslides had been met before Mitch 

rainfall started, which is a reasonable 

assumption because Mitch occurred at the 

end of the rainy season, then about 275 mm 

in 6 days (an average of 46 mm/ day) could 

be considered an estimate for the triggering 

rainfall for the La Lima landslide. However, 

because the La Lima landslide occurred in 

an area of relatively high rainfall compared 

to the rest of the study area (where other 

large landslides occurred), the actual triggering threshold for large landslides was probably less than 275 mm in 6 days. 

The main concentrations of landslides are 

on moderate-to-steep hillslopes underlain by 

various geologic units. For the purpose of 

describing the mapped landslides, we divide 

the study area into five distinct regions based 

on differing geologic and geomorphic characteristics. These regions include the upper 

Polochic valley and surrounding highlands, 

the central Sierra de las Minas, the hills surrounding La Union and Zacapa, the eastern 

Sierra de las Minas, and the border region 

with Honduras. All of these areas received 

between 200 mm and 600 mm of rain over a 

13-day period between October 25 and 

November 6 (plate 21). The highest rainfall 

amounts (400 mm to 600 mm) occurred in 

the Upper Polochic valley and surrounding 

highlands and in the central Sierra de las 

Minas. The lower rainfall amounts (200 mm 

to 400 mm) occurred in the hills surrounding 

La Union, the eastern Sierra de las Minas, 

and in the border region with Honduras. In 

general, the rainfall received in these areas is 

roughly equivalent to the average precipitation received in a 1-year period (see precipitation section earlier in report). Below, we 

describe some of the landslides in each of 

the five regions. 

12
Figure 6. Precipitation 

during 1999 in the Sierra 

de las Minas at rain gage 

stations San Lorenzo (A) 

and Pasabien (B). 

13
14

Upper Polochic Valley and 

surrounding Highlands

Hurricane Mitch triggered landslides

throughout the upper Polochic Valley and

the surrounding highlands (plates 1-5), one

of the primary coffee-growing areas in

Guatemala. This is also an area of steep hillslopes, high relief, and Quaternary earthquake activity along the Polochic fault.

Erosion along the Polochic fault formed the

valley. The highlands on the north side of

the valley are predominantly underlain by

calcareous rocks and are known for their

spectacular karst topography. The highlands

on the south side of the valley are predominantly underlain by metamorphic and clastic

sedimentary rocks. Below, we discuss some

of the landslides in the region.

Cobán Quadrangle (plate 1)

Landslides in the vicinity of Cerro Xalijá 

The primary concentration of landslides

on the Cobán quadrangle (plate 1) is near

Cerro Xalijá on the headwaters of the Río

Chilax and the Río Meslelá, about 12 to

17 km southeast of Cobán. Villages in this

area include Campat, Chitix, and Xucaneb.

The area is underlain by Jurassic and

Cretaceous carbonate rocks (Bonis and others, 1970; Paulsen, 1976). There are about

150 landslides in the Cerro Xalijá area.

Elevations of landslide initiation locations

range from about 1,500 to 2,100 m. These

landslides are shallow (generally less than

about 3-5 m deep) and encompass areas of

less than 1 ha. Many mobilized into debris

flows. There is also one earthflow that was

mapped in this area at UTM coordinates

793200 m E and 1703100 m N.

Tactic Quadrangle (plate 2)

Rotational landslide near Cuyquel

Large rotational landslides were rather

rare in the study area. One example is the

large rotational landslide shown on figure 8

located near Cuyquel, about 3.5 km southeast of Tactic on the Tactic quadrangle

(plate 2). The area is underlain by

Carboniferous to Permian shales, siltstones,

Figure 7. Cumulative precipitation in the Sierra de las Minas at rain gage stations San Lorenzo and Pasabien 

during 1999. Value for day of Quebrada Sucia debris flow shown by open symbol on the San Lorenzo data series.
sandstones, conglomerates, and phyllites. It 

lies about 1 km south of the mapped trace of 

the Polochic fault (Bonis and others, 1970; 

Nicolaus and Muller, 1979). The landslide is 

at the intersection of the Río Frio and the 

Río Cahabon, on the east side of Highway 

CA14. The landslide is about 225 m wide 

and 100 m long (about 2.5 ha in area) and 

partially blocked the Río Cahabon. The elevation at the head of the slide is about 

1,530 m. The gradient of the undeformed 

hillslope above the landslide ranges from 20o 

to 30o. We examined the headscarp of the 

landslide and found a well developed, clayrich soil formed on a brecciated siltstone 

and/or phyllite. The soil profile included, 

from top to bottom, a 10-30 cm thick, gray 

to black A horizon, and an 80-cm-thick B 

horizon that was comprised of a 50-cm-thick 

red horizon, and a 30-cm-thick whitishyellow horizon. The underlying brecciated 

rock had a soft, clay-rich matrix that resembled gouge. Blocks of breccia ranged up to 

about 10 m by 10 m in two dimensions. We 

observed old landslide scars at the east end 

of the landslide and fresh scarps above these 

scars. The fresh scarps, which cross relatively intact and in-place landslide blocks, indicate that the east end of the landslide is 

unstable and may be susceptible to future 

Figure 8. Large rotational landslide near Cuyquel; landslide is about 

225 m wide and 100 m long. View is to the northeast. UTM coordinates 

887650 m E, 1694000 m N. Photo taken January 4, 2001. 

failure. The brecciated nature of the bedrock 

and the old landslide scars indicate that this 

area may be preferentially susceptible to 

future landslides as compared to surrounding 

areas. 

Landslides on the north flank of the 

Sierra de Chuacus 

On the south side of the Río Polochic, the 

north flank of the Sierra de Chuacus in the 

Tactic quadrangle (plate 2) is preferentially 

susceptible to landslides as compared to the 

surrounding areas. The susceptible area is 

bounded on the west by the Hacienda 

Cumbre de Rocjá and on the east by the 

Quebrada Muxilija. During our mapping, we 

noticed numerous old (Quaternary) landslide 

scars and deposits in this area. We mapped 

about 50 landslides that were triggered by 

Hurricane Mitch, and three pre-Hurricane 

Mitch landslides in this area. The reason that 

this area is landslide prone is unclear. The 

area is underlain by Permian siltstones 

interbedded with limestone and fine-grained 

sandstones (Nicolaus and Muller, 1979), but 

so is much of the surrounding area that did 

not have an abundance of Quaternary landslides. A more detailed study of the physical 

properties of the bedrock and colluvial soil 

in the area is needed to accurately assess the 

reason for the preferential susceptibility. 

Tucurú Quadrangle (plate 4) 

La Concepción Landslide 

One of the largest landslides in the upper 

Polochic Valley is near the Finca La 

Concepción, about 3 km southwest of 

Tucurú on the Tucurú quadrangle (plate 4). 

The landslide shown on figure 9 is about 

700 m wide and 250 m long (about 18 ha in 

area) and destroyed several houses in the village of Amapola. Landslide movement 

appears to have been predominantly translational. The head of the landslide is at an elevation of about 1,140 m. Existing geologic 

mapping (Paulsen, 1980) indicates that the 

landslide is underlain by siltstone interbedded with limestone. Eyewitness accounts 

indicated that some initial movement of the 

landslide was triggered by an earthquake 

that shook the area about 1 year before 

Hurricane Mitch, but that catastrophic movement occurred about 14 days after the start 

15
Figure 9. La Concepción landslide near Tucurú; landslide is about 700 m 

wide and 250 m long. View is to the west. UTM coordinates 808000 m E, 

1690500 m N. Photo taken January 5, 2001. 

Figure 10. Landslide typical of the area northwest of Senahú; landslide is 

about 70 m wide and 400 m wide. View is to the north. UTM coordinates 

193850 E, 1711100 N. Photo taken January 6, 2001. 

of Hurricane Mitch rainfall. Other eyewitnesses stated that the slide moved catastrophically during Mitch, and then moved 

again about 14 days later during a second 

earthquake. In all accounts, the landslide 

moved slowly enough that residents of houses on the landslide mass had time to evacuate. 

Senahú Quadrangle (plate 5) 

Landslides northwest of Senahú 

One of the primary concentrations of 

landslides on the Senahú quadrangle (plate 

5) is on the headwaters of the Río 

Seritquiche, Río Sepec, and Quebrada 

Setzimaj about 5 to 10 km northwest of 

Senahú. Villages and farms in this area 

include Sejocob, Sechich, Secareché, Vado, 

Finca Semarac and Finca Chirreaj. The highest landslide concentrations are near 

Sejocob. The area is at and near the faulted 

contact between Cretaceous and Permian 

carbonate rocks (Bonis and others, 1970). 

Vegetation in the area is either forest or 

cleared land. Elevations of landslide initiation locations range from about 1,000 m to 

1,400 m. Landslides in this area are typically 

shallow (generally less than about 3-5 m 

deep) and encompass less than 3 ha (fig. 10). 

Many mobilized into debris flows. 

Landslides above La Tinta 

Another concentration of landslides on 

the Senahu quadrangle (plate 5) is on the 

south flank of the Montaña Piedras Blancas, 

above La Tinta. These landslides damaged 

coffee and cardamom crops and contributed 

sediment to numerous streams. Floods in six 

of the drainages carried sediment to the Río 

Polochic (plate 6). Floods in two of the 

drainages flowed around the edges of La 

Tinta and apparently did not affect the town. 

Most of the landslides are on moderateto-steep hillslopes directly below the steepest hillslopes on the flank of the Montaña 

Piedras Blancas. Landslides initiated at elevations ranging from about 500 to 1,400 m 

and ranged in area from less than 1 ha to 

about 16 ha. Areas where landslides initiated 

are underlain predominantly by Paleozoic 

metamorphic rock, and to a lesser extent by 

Permian carbonate (Bonis and others, 1970). 

The largest landslide (fig. 11) is on a hill 

16
with gradients ranging from 45o to 50o. The 

failure appeared to be at the bedrock/colluvial contact at depths that ranged from 2 m 

to 10 m below the surface. Eyewitness 

accounts indicate that the landslide occurred 

during a 24-hour period starting on or about 

November 1. 

Scarps and elongate depressions 

at the edge of the karst highland 

There were several features that we 

observed during our mapping and reconnaissance that are worthy of description even 

though they were not created by Hurricane 

Mitch. One of the most interesting of these 

features was a series of scarps and elongate 

depressions (fig.12) located in the southwest 

corner of the Senahú quadrangle (plate 5) in 

an area underlain by Permian carbonate rock 

(Bonis and others, 1970). The features are at 

and near the edge of the karst highland, just 

above the steep southern flank of the 

Montaña Yalijux and the Montaña Piedras 

Blancas. The features trend between N20°E 

and N90°E, which is parallel to sub-parallel 

to the steep flank. Some of the features closest to the steep flank appear to be uphill-side 

down scarps that have created elongate 

closed depressions (fig. 12). These characteristics are typical of gravity-spreading features (trenches and grabens collectively 

Figure 11. Landslide on the south flank of the Montaña Piedras Blancas 

above La Tinta. View is to the north. UTM coordinates 185200 m E, 

1700100 m N. Photo taken January 15, 2001. 

known as sackungen) that have been 

described in the mountains of the U.S. and 

Europe (for example, see Varnes and others, 

1989). The location of the scarps and 

depressions is consistent with the setting of 

many sackungen; that is, along ridges or 

plateaus that are bounded by very steep 

flanks. The major difference is that in the 

U.S. and Europe sackungen typically are in 

terrain that has been oversteepened by 

glaciation, while this has not been the case 

in Guatemala. In the Senahú quadrangle, the 

flank of the plateau is very steep, probably 

because of differential uplift and erosion 

along the Polochic fault. Another possible 

origin for the features is that they are simply 

fractures (possibly related to the Polochic 

fault) that have been expanded by dissolution of calcareous rock. Without a detailed 

study of the features, however, their exact 

origin and any associated hazard is 

unknown. 

Central Sierra de las Minas 

The middle-to-high elevations of the 

Sierra de las Minas form the largest concentration of landslides (see map of landslide 

locations, plate 21) in the study area (plates 

6, 8, 9, and 11). The area is rugged, with as 

much as 2,700 m of relief from the crest of 

the range at 2,948 m to the foot of the range 

at about 200 m. Above about 1,000 m, the 

area is heavily forested; lower elevations 

have variable amounts of cleared land or are 

covered by scrub vegetation. Most of the 

area is underlain by Paleozoic metamorphic 

rock, including phyllite, schist, gneiss, marble, and migmatite. Serpentinite and granite 

and diorite intrusives ranging from Tertiary 

to Paleozoic age are locally present. Shale, 

sandstone, conglomerate, and phyllite of 

Upper Paleozoic age flank the north side of 

the central part of the range (Bonis and others, 1970). 

Most of the slides were relatively shallow, 

typically involving a layer of colluvium less 

than about 5 m thick and underlying blocks 

of jointed bedrock. A few deep-seated slides 

transported blocks of bedrock as much as 

20 m in diameter. The landslides form two 

primary patterns on the maps. One pattern, 

shown on figure 13 consists of slides that are 

17
Figure 12. Elongate depressions and scarps at the southern edge of the 

Montaña Yalijux. View is to the northwest. UTM coordinates at the 

approximate center of the trench 178350 E, 1698275 N. Photo taken 

January 6, 2001. 

Figure 13. Landslides typical of the central part of the Sierra de las Minas 

at elevations between 1200 and 1800 m (plate 11). Photograph taken to 

northwest above the Río Mojanal. Center of view at UTM coordinates 

232100 m E, 1679400 m N. 

small and isolated, typically 20-50 m wide 

and as much as 100-200 m long (0.2–1 ha). 

The other pattern consists of larger slides 

that mobilized into debris flows and flowed 

down drainages. These form a dendritic pattern on the maps that mimics the drainage 

pattern. Slides in this group are as much as 

25 ha, but on average cover between 1 and 

5 ha. Large slides commonly initiated at or 

near the crest of ridges high on the headwalls of steep, amphitheatre-shaped basins. 

Prominent examples of these large landslides 

are at the head of Río La Lima (plate 9, 

Cover) and on the east side of Cerro Picudo 

(plate 11). 

Landslide scars that pre-date Hurricane 

Mitch are widely distributed in the central 

Sierra de las Minas. These pre-Mitch landslides are abundant on some quadrangles 

(see, for example, the La Tinta quadrangle, 

plate 6). The pre-Mitch landslides are 

expressed as vegetated topographic depressions similar in outline and form to 

Hurricane Mitch landslides, but with more 

subdued morphology. Vegetation on the preMitch landslides is smaller and less dense 

than in adjacent terrain outside the landslide. 

In general, the material transported downslope from the pre-Mitch landslides lacks 

topographic expression and was not mapped. 

Río Hondo Quadrangle (plate 9) 

Río La Lima 

Two landslides along the Río La Lima 

upstream from the town of Jones (figs. 14A, 

B) are the largest landslides in the central 

part of the Sierra de las Minas. Both of these 

slope failures were dip-slope, rock and 

debris slides on steep hillslopes in granitic 

gneiss (Newcomb, 1978) along the west wall 

of the canyon of the Río La Lima (Schuster 

and others, 2001). The lower of the two 

slides (area about 16 ha; toe location about 

4 km north of the town of Jones) dammed 

the Río La Lima (figs. 15 and 16). The 

upper of the two slides, shown on the cover, 

(area about 25 ha; toe location about 5.5 km 

north of Jones) initiated at the head of the 

Río La Lima on November 1, 1998, and preceded the lower slide by 1 day (Jorge Mario 

Aldana Ramirez, personal commun., January 

2000). Subsequent erosion of the debris-flow 

18
15 

B 

Figure 14. A. Index map of area of landslide 

dam on Río 

and 

La Lima. 

B. Map showing areas (shaded) affected by 

landslides, debris flows, and flooding in the 

upper Río La Lima drainage. Dark shading 

shows the landslide complex that produced 

16. 

the 

landslide dam. Arrows show the approximate 

photo points and directions of view of figures 

19
deposits mobilized from the upper slide contributed much of the sediment that fills the 

impoundment behind the landslide dam. The 

upper slide initiated at an elevation of 

1,820 m, and debris-flow deposits, flood 

scour (fig. 17), and flood deposits are continuous along the Río La Lima and its continuation, Río Jones, for 14.5 km to the 

Motagua River at an elevation of about 

150 m. Locally, the river channel was 

scoured down to bedrock (fig. 17). These 

two large landslides and related deposits 

along the Río La Lima and Río Jones are 

clearly visible on a Landsat Thematic 

Mapper image of the area taken December 4, 

1998, from an altitude of 705 km (image ID 

LT5019050009833810). 

Stratigraphic studies by Tobisch (1986) 

show that debris flows along the piedmont at 

the southern foot of the Sierra de las Minas 

have been an ongoing process for most of 

Quaternary time (past 1.8 m.y.). Major 

drainages from the Sierra de las Minas in the 

central Motagua Valley have locally wellpreserved terraces covered by boulders and 

underlain by sediment characteristic of 

debris flows. Large boulders cover extensive 

areas of the alluvial fan surface associated 

Figure 15. Landslide dam on the Río La Lima, 

looking upstream (north) from a point 4 km 

north (upstream) of Jones (see fig. 14); photograph taken 25 January 2000. The landslide 

originated on the steep slope in the upper left 

corner of the photograph. The point of discharge of the river from the debris that forms 

the dam is at the point where the water is first 

visible at the middle right part of the photograph. 

Figure 16. Oblique aerial view to north of the landslide that produced the 

dam on the Río La Lima; photograph taken 12 January 2001. Smooth eventoned surface crossed by Río La Lima at the toe of the landslide is the sediment fill behind the landslide dam. 

20
Figure 17. Scoured channel on the Río La Lima (UTM coordinates 

227337 m E, 1674690 m N) about 1 km downstream from the landslide 

dam shown on figures 15 and 16. 

Figure 18. Coarse boulders on surface of alluvial fan near 

Piedra de Afilar. 

with the Río Jones drainage; fields of these 

boulders are conspicuous along Highway 

CA9 in the vicinity of Piedra de Afilar 

(fig. 18), about 6 km east-northeast of Río 

Hondo. Late in its development, Río Jones 

was captured by a nearby drainage east of its 

former channel near Mal Paso, leaving much 

of the fan without a source for continued 

deposition. Relict channels as narrow as 2-3 m 

wide and with levees characteristic of debris 

flows, are well-preserved on the old fan surface suggesting that the fan was abandoned 

recently, perhaps within the past few thousand years. Although the large debris flows 

in area associated with Hurricane Mitch are 

historically unique, the geologic record 

shows that they are part of a long-term 

process. 

Quebrada Sucia 

The rainy season of 1999 was unusually 

wet, and on September 17, 1999, a series of 

debris flows initiated in the steep headwall 

amphitheater of Quebrada Sucia, 7 km 

northwest of Río Hondo (plate 9) and coalesced in the channel of Quebrada Sucia. 

The debris flow crossed Highway CA9, 

engulfing several vehicles. Boulders 3-4 m 

in diameter are common in the debris-flow 

deposits (fig. 19), and the velocity of the 

debris flow was great enough to elevate 

deposits on the outside of some curves 2-3 m 

higher than deposits on the inside of the 

curve. 

A local resident whose farm adjoins 

Quebrada Sucia north of Highway CA9 said 

that it was not raining at his home at the 

time of the debris flow, but he believed that 

there was a big storm in the mountains at the 

head of Quebrada Sucia. He reported that 

the first debris to come down the drainage 

was a mixture of logs, rocks, and mud, with 

large boulders being deposited at that time. 

That was followed about 2 hours later by a 

flood of water (Sergio Antonio Aparicio, 

oral commun., January 2000). 

Because the aerial photographs used to 

map the debris flow deposits shown on plate 

9 were taken sometime between January and 

March 2000, we cannot preclude the possibility that some of the landslides shown in 

the Quebrada Sucia drainage were not triggered by Hurricane Mitch. In fact, no debris 

flow in the drainage was observed by resi21
dents of the area during Hurricane Mitch, 

and the large volume of debris transported 

by the 1999 debris flow suggests that the 

slides shown in the drainage originated in 

September 1999. 

Sierra de las Minas Quadrangle 

(plate 11) 

Disappearing drainage in the 

Río Zarquito area 

Sediment from a landslide in the northeast quadrant of the Sierra de las Minas 

quadrangle (plate 11) follows an unnamed 

drainage to the north-northeast for about 

3 km to an abrupt end at a closed depression 

at a natural barrier in the drainage (UTM 

247600 m E, 1693600 m N). There is no 

ponding or accumulation of sediment in the 

depression. The area has karst morphology, 

and the barrier was probably caused by subsidence above a cavern. The channel of a 

drainage that originates at the foot of a steep 

hill 1.7 km to the north-northwest is filled 

with fresh sediment with no apparent 

source. We infer that sediment was transported underground from where the sediFigure 19. Coarse boulders along margin of debris flow in Quebrada Sucia 

about 1 km north of Highway CA9. Note sharp trim line at edge of vegetation on left side of photograph. Large boulder in brush is from a previous 

debris flow. Post-debris flow flooding removed most of finer debris-flow 

matrix from the upper part of the boulder deposit. Photograph taken 

January 26, 2000. 

ment disappears at the closed depression in 

the channel to the south-southeast. 

La Union and Zacapa Quadrangles 

(plates 10 and 13) 

There were several areas of moderate-todense concentrations of landslides in the 

hills surrounding La Unión and Zacapa 

(plates 10 and 13). The hills are generally 

moderate in steepness and reach a maximum 

elevation of about 1,800 m near the center of 

the La Unión quadrangle. In general, above 

elevations of about 1,000 m the area is heavily forested, whereas lower elevations have 

variable amounts of smaller, less dense vegetation or cleared land. The area is underlain 

by Paleozoic metamorphic rocks, prePermian to Tertiary intrusive rocks, and 

Tertiary and Quaternary volcanics (Bonis 

and others, 1970). Most of the landslides 

occurred in the La Unión quadrangle on hillslopes underlain by metamorphic rocks. 

According to residents of La Unión, landslides closed the road on both sides of the 

town on the night of October 30 or early in 

the morning of October 31. The town was 

then isolated for about 1 month while the 

landslides were cleared from the road. 

Below, we describe four main concentrations 

of landslides, three on the La Union quadrangle and one on the Zacapa quadrangle. 

The first concentration of landslides and 

debris flows is in steep topography on the 

headwaters of the Río Timushán and the 

Quebrada Colorado, about 3-7 km south of 

La Union (plate 13). The landslides initiated 

from an area underlain by metamorphic rock 

at elevations between about 1,100 m and 

1,500 m. Most of them were probably less 

than 3 m deep and covered less than 1 ha. 

Material from these landslides and debris 

flows was deposited in downstream channels. Flooding and undercutting along these 

channels contributed to the initiation of several large landslides along the channel banks. 

Several roads that crossed these channels 

were washed out by flooding. 

The second concentration of landslides is 

in steep topography in and near the towns of 

Talquezal and Volcan (plate 13). Most of the 

landslide activity was 1 to 7 km west of the 

towns, but we also observed several landslides near the towns that destroyed coffee 

22
Figure 20. Landslides on the La Unión quadrangle. Prominent 


landslide in right foreground is at UTM coordinates 243175 E, 1648650 N.


Figure 21. Large landslide on the La Unión quadrangle at UTM


coordinates of 245000 E, 1647700 N.


fields and roads. Most landslides in these 

areas were similar to those near La Unión as 

described above; that is, they were shallow 

and small and in steep topography underlain 

by metamorphic rock at elevations above 

1,000 m (fig. 20). The main exception to this 

observation is a large translational landslide 

about 1.5 km southwest of the town of 

Talquezal (fig. 21). This landslide is about 

350 m long and as much as about 150 m 

wide (about 5 ha). This slide deposited sediment in downstream areas, but apparently 

did not cause damage to fields or residences 

on the hillslope. Until this slide becomes 

vegetated, it will continue to be a source of 

sediment in downstream areas. According to 

residents of Talquezal, this landslide failed 

rapidly at about 10 a.m. on November 1, 

1998. 

The third concentration of landslides is 

along the Río Grande o Jocotán in the southwest corner of the La Unión quadrangle. 

This concentration consisted mostly of 

debris flows with long flow paths (commonly longer than 700 m) that terminated in the 

river. Most of the debris flows originated 

from an area underlain by intrusive rock 

from what appear to be the steepest hillslopes in the La Union quadrangle. 

Elevations of initiation locations for the 

landslides range from 500 m to 1,100 m. 

The debris flows formed small fans in the 

channel of the Río Grande o Jocotán. Above 

its intersection with the Quebrada de 

Lanchor, the channel appears to have been 

scoured to bedrock by flooding. Downstream 

from this intersection, deposition and lateral 

erosion were the dominant processes. 

Railroad tracks near the intersection of the 

Río Grande o Jocotán and the Río Grande de 

Zacapa were damaged by lateral erosion during flooding. 

The fourth concentration of landslides is 

about 3 km southwest of El Conacaste on 

the Zacapa quadrangle (plate 10). These 

landslides are on moderately steep hillslopes 

underlain by Quaternary volcanic rock at 

elevations between 1,100 m and 1,200 m. 

The landslides initiated from old landslide 

scars and deposits formed on the volcanic 

rocks. The landslides were probably less 

than 3-5 m in depth and generally covered 

less than 3 ha, but contributed a large 

23
amount of sediment to downstream channels. 

Because there are very few landslides in 

adjacent steeper areas underlain by intrusive 

and metamorphic rocks, it appears that the 

location of the landslides was strongly controlled by the physical properties of the colluvial soil mantle formed on the Quaternary 

volcanic rocks; that is, the geology made the 

area more susceptible to landslide occurrence. 

Eastern Sierra de las Minas and 

Montañas del Mico 

The eastern Sierra de las Minas (plates 

14, 15, and 17), and its eastern extension, 

the Montañas del Mico (plates 16 and 19), 

form a relatively narrow, elongate mountain 

range that occupies a position south and east 

of Lago de Izabal and north of the Río 

Motagua. Elevations are low compared to 

the central part of the Sierra de las Minas; 

they reach a maximum of about 940 m in the 

Los Amates quadrangle (plate 15) and generally decrease to the east. Unlike the central 

Sierra de las Minas, which is predominantly 

underlain by metamorphic rock, the eastern 

Sierra de las Minas is underlain by a variety 

of rocks including serpentinite of unknown 

age, Permian to Cretaceous carbonate rock, 

Paleozoic metamorphic rock, and 

Carboniferous to Permian shale, sandstone, 

conglomerate, and phyllite (Bonis and others, 1970; Muller, 1977). The highest concentrations of landslides are located in the 

Los Amates (plate 15), Mariscos (plate 14), 

Castillo San Felipe (plate 16), and Entre 

Ríos (plate 19) quadrangles. 

Mariscos Quadrangle (plate 14) 

Landslides south of Mariscos 

The primary concentration of landslides 

on the Mariscos quadrangle (plate 14) is on 

the flanks of several unnamed peaks in an 

uninhabited area about 4-9 km south of 

Mariscos. One of the highest peaks in the 

area is identified by benchmark “Cachirul” 

(elevation 844 m). Hillslopes in the area are 

moderate to steep. The area is forested on 

the east side of the Río Carcaguatalilla, and 

grass covered (logged) on the west side of 

the Río Carcaguatalilla. The area is just to 

the north (0-4 km) of one of the mapped 

traces of the Motagua fault (Bonis and others, 1970). The lithology of rocks in the area 

is diverse and consists of serpentinite of 

unknown age, Cretaceous carbonate, and 

Carboniferous to Permian shale, sandstone, 

conglomerate, and phyllite. Landslides initiated at elevations ranging from about 300 m 

to 800 m and ranged in area from less than 

1 ha up to about 3 ha. Many landslides 

mobilized into debris flows. There are also 

several earthflows in the area, primarily on 

the grass-covered hills on the west-side of 

the Río Carcaguatalilla. One of these earthflows is described in the following section. 

Piedra Parada Earthflow 

Several earthflows are on the grasscovered hills of the Finca Piedra Parada on 

the west side of the Río Carcaguatalilla. We 

examined one of these earthflows in the 

field and have informally named it the 

Piedra Parada earthflow. The Piedra Parada 

earthflow (fig. 22) is about 250 m long, 

50 m wide, and 1 m to 2 m deep. The head 

of the earthflow is at an elevation of about 

490 m. The earthflow occupies a position at 

the bottom of a small drainage on a northeast-facing hillslope. The basal slip surface 

of the earthflow is at the top of underlying 

serpentinite bedrock, which has been polished and striated by movement of the earthflow. The earthflow material is composed of 

a red, colluvial-soil matrix that contains a 

moderate number of cobble- to bouldersized serpentinite clasts. The uppermost part 

of the earthflow includes several internal 

extensional scarps. The middle and lower 

portions have several compressional (thrust) 

scarps. 

This earthflow appears to have moved in 

at least two phases. The first phase of movement involved colluvial soil in the lower 

part of the drainage channel. This material 

moved directly down the channel and then 

to the south as it cleared the front of the hillslope. The second phase of movement 

involved colluvial soil in the upper and 

lower portions of the drainage. This material 

flowed down the channel and to the north as 

it cleared the front of the hillslope. Within 

the channel, movement was translational on 

top of the bedrock surface. Beyond the hillslope front, the earthflow pushed, and flowed 

24
Figure 22. The Piedra Parada earthflow. View is to the west. UTM 

coordinates 273100 E, 1698725 N. 

over, footslope colluvial soils, channel alluvium, and possibly old landslide deposits. 

A portion of the hillside that failed as a 

debris slide is exposed on the side of the 

north flank of the earthflow, in the upper 

part of the channel. The failure occurred during or after movement of the upper part of 

the earthflow. The exposure reveals rubbly, 

disaggregated, serpentinite bedrock. At the 

base of this exposure is the deposit from the 

debris slide, which rests within and on top of 

earthflow material. 

Interviews with farmhands and the owner 

of the Finca Piedra Parada indicated that the 

area surrounding the earthflow was logged in 

about 1995. One farmhand who had worked 

on the farm for 35 years indicated that he 

had not observed any landslide activity in 

the area prior to Hurricane Mitch, including 

1974, when he said there was rainfall similar 

to that during Hurricane Mitch, and in 1976, 

during the M=7.5 earthquake on the 

Motagua fault (see Harp and others, 1981). 

These observations suggest that the area was 

less susceptible to landslide activity prior to 

logging. 

Los Amates Quadrangle (plate 15) 

Landslides northwest of Los Amates 

A prominent northeast-trending zone of 

landslides about 9 km northwest of Los 

Amates was strongly controlled by the geology of the area. Landslides in the zone 

formed on Paleozoic phyllite and schist on 

the steep southeast flank of Montaña de 

Colombia at elevations between 400 m and 

900 m. An abrupt decrease in the density of 

landslides southeast of the zone coincides 

with the thrust fault boundary between the 

phyllite and schist to the northwest where 

the density of landslides is high and serpentinite to the southeast (Muller, 1977), where 

the density of landslides is low. 

Castillo San Felipe and Entre Ríos 

Quadrangles (plates 16 and 19) 

There are several moderate-to-dense concentrations of landslides near the study area 

boundary on the Castillo San Felipe (plate 

16) and Entre Ríos (plate 19) quadrangles. 

The position of the landslides close to the 

border indicates that there may be additional, 

unmapped landslides in the hills north of the 

border. The majority of landslides on the 

Castillo San Felipe quadrangle are on moderate-to-steep hillslopes near the Río San 

Marcos and 4 km to 10 km northeast of 

Highway CA13. Landslides on the Entre 

Ríos quadrangle are on moderate-to-steep 

hillslopes, 2 to 6 km north of Highway CA9. 

Individual landslides on both quadrangles 

generally cover less than 1 ha and initiated at 

elevations ranging from 200 m to 600 m. 

Both quadrangles are underlain by 

Cretaceous carbonates and Carboniferous to 

Permian shale, sandstone, conglomerate, and 

phyllite. One large landslide on the Entre 

Ríos quadrangle dammed a tributary of the 

Río Tenedores (see landslide dam at UTM 

321200 E, 1723200 N). We do not know if 

this natural dam is retaining water upstream. 

Guatemala-Honduras Border Region 

In general, the density of landslides 

appears to increase to the southeast in the 

vicinity of the Guatemala-Honduras border 

in eastern Guatemala (e.g., Cerro Caral 

quadrangle, plate 20). We also observed, but 

25
did not map, a high density of landslides in 

Honduras by scanning aerial photographs 

from east-west flight lines that extend into 

Honduras. 

Juyamá Quadrangle (plate 18) 

In the mountainous part of the Juyamá 

quadrangle (plate 18), there were no aerial 

photographs from the IGN-NIMA mapping 

mission used elsewhere in this study. 

However, we obtained 1:30,000-scale aerial 

photographs taken in March 1999 from 

Aerofoto Centroamericana, S.A. for part of 

the area and used them to map an area near 

the Guatemala-Honduras border. The density 

of landslides in part of the mapped area is 

the highest seen in our study, with as many 

as 120 mapped landslides in a 1 km2 area. 

Much of the mapped area has been cleared 

of trees; landslides in the cleared areas typically involved only a surface layer of vegetation and an underlying layer of colluvium 

and weathered bedrock (Paleozoic metamorphic rocks; Bonis and others, 1970) up to 

1-2 m thick. Most of the landslides are at 

elevations between 500 and 1,000 m. By the 

time of our field visit to the area in January 

2001, the landslides scars were revegetated 

except for the steep scarps at the heads of 

some slides. 

A farmer who lives in the central part of 

the area (UTM 291 583E, 1 686 039N) 

reported that following about 8 days of rain, 

there was an intense rainstorm (“tormenta”) 

that lasted about 3 hours. When the storm 

stopped all of the landslides in the area 

around his farm occurred about a half hour 

after the storm. At one landslide on his farm, 

his children were working in a field on the 

slide and ran out of the field as the hillside 

began to fail. Failure of the hillside took 

place within a period of about 5 minutes. 

Landslide Susceptibility Mapping on the 

Pueblo Viejo and Río Hondo 

Quadrangles 

The Pueblo Viejo (plate 8) and Río 

Hondo (plate 9) quadrangles were selected 

to demonstrate the utility of landslide-susceptibility mapping because they include 

abundant pre-Hurricane Mitch, Hurricane 

Mitch, and post-Hurricane Mitch landslides 

that were initiated on a variety of slope gradients and impacted the built environment. 

Additionally, the La Lima landslide, which 

is modeled in a later section of this report, is 

on the Río Hondo quadrangle. The number 

of mapped landslides that were triggered by 

Hurricane Mitch in the two quadrangles is 

2,951. We have used the Hurricane Mitch 

landslides to develop a landslide susceptibility map for the prolonged, elevation-controlled rainfall associated with Mitch. We 

have used the pre- and post-Hurricane Mitch 

landslides to evaluate the susceptibility map. 

Landslide susceptibility can be derived 

using a number of different methods 

depending on the data that are available 

(Soeters and van Westen, 1996). In many 

methods, physical properties of hillslope 

materials, as well as gradient values from a 

digital elevation model (DEM), are used in a 

slope-stability model to estimate varying 

levels of susceptibility. On the Pueblo Viejo 

and Río Hondo quadrangles, geologic mapping is incomplete and physical-property 

data are not available. Therefore, the susceptibility map that we created was based only 

on landslide locations and data that were 

derived from a DEM. In order to determine 

the factors that contribute to landslide susceptibility, we use the DEM to determine 

elevation, gradient (slope of ground surface), 

topographic curvature, and aspect (direction 

of slope) at each landslide-initiation location. We generate frequency distributions for 

each data set where frequency is expressed 

as the percentage of the total number of 

landslide-initiation locations. The frequency 

distribution of each landslide-initiation data 

set (example given, gradients at landslideinitiation locations) is then compared to the 

frequency distribution of the entire population of data within the two quadrangles 

(example given, gradients of all 10-m cells 

within the study area). Finally, a ratio 

between the frequency distribution for each 

landslide-initiation data set and the corresponding frequency distribution of population data is computed (see Wieczorek and 

others, 1988; and Coe and Godt, 2001, for 

other examples of this approach). The logic 

behind this comparison is that each landslide-initiation data set is a subset of the corresponding population data set and that ratio 

26
values above a value of one identify areas 

within the frequency distributions that were 

preferentially susceptible to landslides during the triggering event. Below, we first 

describe how our DEM was created, then 

follow with a description and analysis of elevation, gradient, curvature, and aspect, and 

lastly present a susceptibility map based on 

results from our analyses. 

Creation of the DEM 

We use a 10-m resolution DEM that was 

generated from 20-m contours on the 

1:50,000-scale quadrangles. The DEM was 

created using a drainage-enforced, inversesquare, weighted-average algorithm. The 

algorithm assigns elevation values to DEM 

cells on the basis of proximity to contour 

lines, that is, the closer a cell is to a contour 

line, the closer the value of that cell is to the 

contour value. The algorithm also uses 

breaklines (lines including varying elevation 

values) along ridges and drainages, to ensure 

that the DEM is hydrologically correct. The 

algorithm produces a DEM that is ideal for 

flow modeling (see LAHARZ modeling in 

the next section) but introduces abrupt 

changes in elevations between DEM cells 

near contour lines. When the DEM is viewed 

as a shaded-relief map, the abrupt changes in 

elevation are visible as steps and terraces on 

the DEM surface. Because these steps and 

terraces could adversely affect our analysis 

of gradient, we processed the DEM used for 

the gradient analysis as follows. First, we 

created a gradient grid using the slope function in ArcInfo. The slope function computes a gradient at each grid cell based on 

the maximum change in elevation from eight 

surrounding cells. Once the gradient grid 

was created, we filtered the grid using the 

focalmean function in ArcInfo. The 

focalmean function computes a mean value 

at each grid cell based on the values of 

neighboring cells. We used a 7 cell (70 m) 

radius to define the neighboring cells used in 

the computation of the mean. We found that 

this processing removed most of the step and 

terrace artifacts. The original DEM was used 

for analyses of elevation, topographic curvature, and aspect. 

Analysis of Elevation 

An elevation was determined for each 

mapped landslide by digitally overlaying the 

landslide-initiation locations on the DEM 

and recording the elevation of the DEM cell 

that was coincident with each landslide-initiation location. About 96 percent of the landslides initiated from elevations between 500 

and 2,500 m (fig. 23 and plate 22). When 

landslide frequency is tabulated for every 

100-m change in elevation, the highest percentage of landslides (about 11.7 percent of 

the total) occurred between 2,000 and 

2,100 m. The entire population of elevations 

at 10-m DEM cells in the two quadrangles 

ranges from 1 m to about 2,990 m (fig. 23). 

The highest percentage of these elevations 

(about 10.6 percent of the total) occurs 

between 200 m and 300 m. The ratio of 

landslide-initiation gradients to the entire 

population of gradients (fig. 23) indicates 

that areas with elevations between 1,200 m 

and 2,800 m, where the ratio is greater than 

1, were preferentially susceptible to landslides during Hurricane Mitch. Available 

rainfall data indicate that these areas were 

probably preferentially susceptible to landslides because they received greater amounts 

of rainfall than areas at lower elevations. 

Although there were only two gages operating in the two quadrangles during Hurricane 

Mitch, data from these gages show that 

about twice as much rain fell at 1,800 m 

(San Lorenzo gage) than at 260 m (Pasabien 

gage). Differences in the density and species 

of vegetation (high density, tropical species 

at higher elevations; low-density, semi-arid 

species at lower elevations) suggest that this 

pattern of rainfall is typical for the region. 

The abundance of landslides at higher elevations (plates 8 and 9) indicates that 

Hurricane Mitch rainfall at higher elevations 

was exceptional for the region. 

Analysis of Gradient 

A gradient was determined for each 

mapped landslide by digitally overlaying the 

landslide-initiation locations on the filteredgradient grid and recording the gradient of 

the grid cell that was coincident with each 

landslide-initiation location. About 96 per27
Figure 23. Histograms of elevations measured from the 10-m DEM. Number of 10-m cells in the study area is about 

10 million. Number of landslides is 2951. Ratio was computed by dividing the percentage of landslide elevations by the 

percentage of study-area elevations for each histogram bin. 

cent of the landslides initiated from gradients between 15° and 45° (fig. 24). When 

landslide frequency is tabulated for every 5° 

change in gradient, the highest percentage 

of landslides (about 26.7 percent of the 

total) occurred between 25° and 30°. The 

entire population of gradients at 10-m DEM 

cells in the two quadrangles ranges up to 

75°. The highest percentage of these gradients (about 16.6 percent of the total) occurs 

between 0° and 5° and between 25° and 30° 

(fig. 24). The ratio of landslide-initiation 

gradients to the entire population of gradients (fig. 24) indicates that most areas with 

gradients between 15° and 55°, where the 

ratio is greater than 1, were preferentially 

susceptible to landslides during Hurricane 

Mitch. There is not a strong positive correlation between ratio and gradient. Such a correlation would indicate that landslide incidence increased as gradient increased. Our 

data seem to indicate that all areas with gradients above about 15° were nearly equally 

susceptible to landslides during Hurricane 

Mitch. This observation, however, does not 

take into account the distribution of gradients with respect to rainfall. 

An analysis of gradient with respect to 

elevation, a proxy for rainfall, provides 

some additional insight into landslide susceptibility. Figure 25 shows the relative percentages of gradients and elevations for 

landslide initiation locations and for a random sample of population cells. We used a 

28
random sample of population cells, as 

opposed to all of the population cells, 

because the large number of population cells 

(about 10 million) made all of the population data difficult to analyze. A ratio of 

these two data sets (fig. 26) shows a distinct 

cluster of preferred susceptibility during 

Hurricane Mitch. The lower bound of the 

cluster forms a relatively straight line that 

can be modeled using the equation y = -23x 

+ 1775, in which y is elevation and x is gradient. This line defines a susceptibility 

threshold, that is, elevations above the line 

had a preferred susceptibility to landslides 

during Hurricane Mitch, and those below 

the line had no preferred susceptibility. The 

left edge of the cluster defines a gradient 

cutoff line, that is, gradients to the left of 

the cutoff (< 9°) had no preferred susceptibility, whereas gradients to the right of the 

cutoff (≥ 9°) were preferentially susceptible. 

The susceptibility threshold makes intuitive 

sense because it indicates that as gradient 

increases, elevation decreases, that is, 

because elevation is a proxy for Hurricane 

Mitch rainfall, the amount of rain required 

to make steep gradients fail is less than that 

required to make shallow gradients fail. 

Analysis of topographic curvature 

Indices of topographic curvature are 

often used to infer the direction and concentration of water flow over a topographic surface and can be used to delineate landforms 

into geomorphic units such as ridges and 

channels (for example, see Gallant and 

Wilson, 2000). Topographic curvature has 

Figure 24. Histograms of gradients measured from the gradient grid. See figure 23 caption for the total number of 10-m 

cells and the number of landslides. Ratio was computed by dividing the percentage of landslide gradients by the percentage of 

study-area gradients for each histogram bin. 

29
30

Figure 25. Diagram showing the

elevations of landslide and study

area cells with respect to corresponding gradients. Study-area

data is from a random sampling

of the total population of 10-m

cells. Percentages were contoured using PTCOUNT software (Savage and others, 2001).

PTCOUNT uses moving countcircle methodology to count data

points. We used a count-circle

size of 2.5 units (elevation and

gradient) and a grid spacing of 1

unit. After counting the counted

points were converted to a percentage of total. The total number of random sample points was

3,299. The number of landslides

is 2,951.

Figure 26. Diagram showing the

ratio of landslide data to studyarea data as shown in figure 25.

Ratios greater than one are preferentially susceptible to landslide

occurrence. Areas of no data are

locations where there were no

randomly sampled study-area

points but there were landslide

points. 
been shown to control the downslope transport of colluvial soils, surface runoff, and 

shallow, sub-surface flow on colluvialmantled hillslopes (Dietrich and others, 

1995). Topographic curvature is typically 

computed from elevations of cells in a 

DEM. Curvature can be computed for the 

entire surface surrounding each DEM cell, 

or the curvature of the surface in a particular 

direction. In this study, we used the curvature function in ArcInfo to compute the curvature of the DEM surface perpendicular to 

the aspect (direction of inclination of ground 

surface) for each cell in the original DEM. 

ArcInfo refers to this type of curvature as 

planform curvature. The curvature function 

computes planform curvature by fitting a 

fourth-order polynomial to nine elevations 

contained in a 3x3 window of cells where 

the center cell is the cell for which curvature 

is being computed. The units of planform 

curvature are 1/100 m. Negative values indicate topography that is concave upward and 

positive values indicate topography that is 

convex upward. Planar surfaces have a curvature of zero. Materials transported by colluvial processes and surface runoff tend to 

accumulate in concave areas. As a result, 

colluvium, colluvial soils, and sediments 

tend to be thicker in concave areas. Some 

studies suggest that concave areas are more 

susceptible to the initiation of shallow landslides (Dietrich and others, 1986). 

We determined a planform-curvature 

value for each mapped landslide by digitally 

overlaying the landslide-initiation locations 

on the grid of curvature cells and recording 

the curvature of the grid cell that was coincident with each landslide-initiation location. 

Ninety-nine percent of the landslides initiated from areas that had planform curvatures 

between –4 and +4 (fig. 27). The highest 

percentage of landslides (about 10.1 percent 

of the total) had curvature values of zero 

(fig. 27) and the landslide curvatures were 

approximately normally distributed about 

zero. As with the landslide curvatures, 

99 percent of the entire population of 10-m 

DEM cells had curvatures that ranged from 

–4 to +4 (fig. 27). The highest percentage of 

these curvatures (about 17.7 percent of the 

total) had values of zero and the curvatures 

were approximately normally distributed 

about zero. The ratio of landslide-initiation 

curvatures to the entire population of curvatures (fig. 27) reveals that both concave 

(curvatures less than zero) and convex (curvatures greater than zero) areas were about 

equally susceptible to landslides during 

Hurricane Mitch. 

Analysis of aspect 

We used the original DEM to create an 

aspect (direction of inclination of ground 

surface) grid using the aspect function in 

ArcInfo. The aspect function determines the 

aspect of each DEM cell by identifying the 

down-slope direction of the maximum rate 

of change in elevation between the DEM 

cell and its neighboring cells. Aspect values 

range from 0° to 359°. An aspect was determined for each mapped landslide by digitally overlaying the landslide-initiation locations on the aspect grid and recording the 

aspect of the grid cell that was coincident 

with each landslide-initiation location. 

When landslide frequency is tabulated for 

every 10° change in aspect, the highest percentage of landslides (about 6.8 percent of 

the total) occurred between 90° and 100° 

(fig. 28). The highest percentage of the 

entire population of aspects for all 10-m 

cells in the two quadrangles (about 4.5 percent of the total) also occurs between 90° 

and 100°. The ratio of landslide initiation 

aspects to the entire population of aspects 

(fig. 28) indicates that east-, southeast-, and 

south-facing hillslopes (aspects between 70° 

and 220°, in fig. 28) were preferentially susceptible to landslides during Hurricane 

Mitch. The reason for this preference is 

unclear. However, one possible explanation 

is that the preference is related to the position and direction of movement of 

Hurricane Mitch. Between October 30 and 

November 1, 1998, when the heaviest rain 

fell in Guatemala, the eye of Hurricane 

Mitch was south of the two quadrangles and 

the direction of movement was from east to 

west (fig. 1). The direction of movement 

and position of Hurricane Mitch may have 

caused east-to-south facing hillslopes to 

receive more rain than west-to-north facing 

hillslopes. 

31
Susceptibility Maps 

As we indicated above, we produce a 

susceptibility map, showing landslide susceptibility during Hurricane Mitch. This 

map shows susceptibility for landslide 

occurrence, but does not show flow paths or 

risk associated with potential landslides. 

The susceptibility map for Hurricane Mitch 

(plate 23) was created using the susceptibility threshold developed using gradient and 

elevation data (fig. 26). All areas with gradients of 9° or greater and elevations above 

the threshold line are shown as being susceptible to landslides. Planform-curvature 

data were not used to create the map 

because our curvature analysis showed that 

landslides occurred in about equal numbers 

on both concave and convex hillslopes. 

Also, we did not use aspect data because we 

were unsure about how to interpret these 

data. These data showed that east-to-south 

facing hillslopes were preferentially susceptible to landslides. Users of the susceptibility 

map should be aware that this preference 

existed for Mitch and that it may exist during future Mitch-like storms. Also note that 

even though some areas where gradients are 

very steep (greater than 50°) are shown as 

being susceptible, figure 24 indicates that 

the percentage of landslides that actually 

occurred on these gradients is very low 

(about 0.5 percent of the total). Additionally, 

note that very steep gradients that lack a colluvial-soil mantle may be susceptible to 

deep-seated, bedrock-involved landslides, 

but are not susceptible to shallow-colluvial 

landslides. 

Figure 27. Histograms of curvatures measured from the planform-curvature grid. See figure 23 caption for the total number 

of 10-m cells and the number of landslides. Ratio was computed by dividing the percentage of landslide curvatures by the 

percentage of study-area curvatures for each histogram bin. 

32
Ninety percent of the mapped landslides 

that were triggered by Hurricane Mitch are 

within the susceptible zone shown on the 

map. Eighty-six percent of the preHurricane Mitch landslides, and all of the 

post-Hurricane Mitch landslides, are within 

the susceptibility zone. The high percentage 

of pre- and post-Mitch landslides that fall 

within the susceptibility zone suggests that 

the positive correlation between elevation 

and rainfall that was observed during 

Hurricane Mitch may also apply to other 

rainstorms. If future studies confirm this 

hypothesis, then the Hurricane Mitch susceptibility map may be applicable for predicting landslide susceptibility during more 

commonly occurring rainstorms. 

One additional way that this hypothesis 

can be tested would be by mapping all of 

the Quaternary landslide scars and deposits 

in the two quadrangles (not just the recent 

ones as in this study). If these landslide features are within the susceptibility zone 

defined in this study, then that would be very 

strong evidence that the Hurricane Mitch 

susceptibility map applies to all rainstorms. 

Another way to test this hypothesis would be 

by studying long-term rainfall characteristics 

from rain gages at varying elevations. Such a 

study might help to determine a rainfall 

threshold for triggering landslides, as well as 

to determine if such a threshold is ever 

exceeded at lower elevations, and how often 

it is exceeded at higher elevations. Existing 

historic landslide data would be particularly 

useful in the development of a landslide-triggering rainfall threshold. 

Figure 28. Histograms of aspects measured from the aspect grid. See figure 23 caption for the total number of 10-m cells 

and the number of landslides. Ratio was computed by dividing the percentage of landslide aspects by the percentage of 

study-area aspects for each histogram bin. 

33
Simulated failure of the landslide dam 

on the Rio La Lima 

Two large landslides triggered by 

Hurricane Mitch affected the Río La Lima 

about 4 km upstream from the town of Jones 

on the Rio Hondo quadrangle (plate 9). The 

lower landslide dammed the river. The landslide dam has an estimated volume of 

500,000 m3 and impounds an additional 

200,000 m3 of water and sediment derived 

from the upper landslide. The likelihood of 

failure of the total 700,000 m3 is considered 

small, but in the event of a strong earthquake, severe rainstorm, or a combination of 

the two, catastrophic failure is possible 

(Schuster and others, 2001). To evaluate the 

potential hazard from catastrophic failure of 

the landslide dam, we applied a GIS-based 

simulation using LAHARZ software 

(Schilling, 1998) to estimate the plainimetric 

and cross-sectional area inundated by the 

resulting debris flow. LAHARZ is written in 

the ArcInfo Macro Language (AML) that 

runs within the GRID module of ArcInfo 

and delimits areas of potential inundation 

from large debris flows or lahars that originate on the flanks of volcanoes. The software uses a digital elevation model (DEM) 

and the results of a scaling and statistical 

analysis of 27 lahars from nine volcanoes to 

estimate cross-sectional and planimetric 

areas of inundation as a function of landslide volumes (Iverson and others, 1998; 

Schilling, 1998). The analysis of Iverson 

and others (1998) and the derived LAHARZ 

software was not specifically intended for 

prediction of inundated areas due to catastrophic failure of landslide dams. However, 

the conditions at the La Lima site are very 

similar to those that the model was designed 

to simulate, that is, the potential debris-flow 

volume is large and reasonably well constrained, and the debris flow would be largely confined to the Río La Lima channel. 

Four simulations were run with debrisflow volumes of 500,000 m3, 700,000 m3, 

900,000 m3, and 1,100,000 m3. This range 

represents failure of the landslide dam 

(500,000 m3) to failure of the landslide dam, 

the impounded sediment and the entrainment of additional material from the upper 

landslide (1,100,000 m3). The results show 

that the LAHARZ simulations clearly define 

hazard zones in areas of low slope adjacent 

to the channel of the Río La Lima (fig. 29). 

The extent of these hazard zones could not 

be delimited by inspection of a topographic 

map alone, thus demonstrating the utility of 

this approach. Comparison of the simulation 

with the mapped extent of the deposit that 

resulted from the debris flow during 

Hurricane Mitch shows good agreement 

with the inundation predicted from a 

700,000 m3 debris-flow volume (fig. 29 and 

plate 9). This result suggests that the volume 

of the debris flow triggered by Hurricane 

Mitch in the Río La Lima drainage was at 

least 700,000 m3. 

SUMMARY 

Hurricane Mitch triggered about 11,500 

landslides in a 10,000 km2 area of east-central Guatemala. On average, this is about 

one landslide/km2 , but ranged up to as 

many as 120 landslides/km2. Rainfall from 

Hurricane Mitch was exceptional because it 

was geographically widespread, prolonged 

over a period of about a week, moderate to 

heavy in intensity, and occurred at the end 

of the rainy season when the ground already 

had a high moisture content. As documented 

in this report, this type of rainfall, on saturated or nearly saturated ground, has the 

capability to trigger both shallow and deepseated landslides over a large area. The 

landsliding documented by this study would 

probably have been less extensive had 

Hurricane Mitch occurred early in the rainy 

season. 

We have made a few limited observations 

regarding rainfall amounts necessary for 

triggering landslides. Specifically, eyewitness accounts at three of the largest deepseated landslides indicated that all three 

occurred on November 1, 1998, near the end 

of Hurricane Mitch rainfall. Rain gage data 

collected near one of these landslides indicates that the slide occurred after 6 days of 

rain that averaged about 46 mm/day. We 

were also able to document rainfall amounts 

that triggered shallow landslides that mobilized into debris flows. These data happen to 

be from debris flows that occurred in 

34
September 1999 but are useful nonetheless. 

In this case, the debris flows were triggered 

during a period of heavy rainfall preceded 

by 1280 mm of antecedent rainfall during 

1999. Rainfall on the day of the debris flow 

was 66 mm, which was comparable to the 

heaviest daily rainfall during Hurricane 

Mitch. 

Areas affected by landslides were typically moderate to steep hillslopes mantled 

by colluvial soil. In several areas, underlying geology played a role, making hillslopes 

preferentially susceptible to landslides. The 

geologic units in these areas were Permian 

siltstone, Quaternary volcanic rocks, and 

Paleozoic phyllite and schist. Many shallow 

landslides typically mobilized into debris 

flows and affected downslope areas, includFigure 29. Inundation areas from LAHARZ modeling of DEM for volumes given on explanation. 

ing less steep hillslopes and drainages. Once 

debris from the flows was in the drainages, 

it was often carried great distances downstream (as much as 14 km) by flooding or 

larger coalesced debris flows. These flows 

often carried debris past mountain or hillslope fronts to major rivers. In particular, 

debris from landslides and debris flows contributed at least a moderate amount of sediment to the Río Motagua and its major tributaries. Areas affected by large landslides 

were similar to shallow landslides, but often 

involved large fragments of bedrock. 

Because of the large volumes of material 

involved and the relatively rapid failure of 

these large landslides, they tended to have a 

more immediate and catastroprophic affect 

on downstream areas. Additionally, the large 

landslides tend to be remaining landslide 

hazards, that is, their source areas remain 

unstable and have the potential to contribute 

moderate to large volumes of sediment to 

downstream locations at least until they 

become revegetated. 

We used 10-m DEMs generated from 

contours on two quadrangles in the central 

Sierra de las Minas to create a map showing 

landslide susceptibility during Hurricane 

Mitch. To create the Hurricane Mitch susceptibility map, we developed a susceptibility threshold equation based on elevation and 

gradient. The analysis indicates that, at least 

on these two quadrangles, gradients less 

than 9o were not susceptible to landslides 

during Hurricane Mitch. Because we can 

show that elevation was a proxy for rainfall 

in these two quadrangles, the slope of the 

line defined by the susceptibility threshold 

equation indicates that less rainfall was 

required to initiate landslides on steep gradients than on shallow gradients. 

We used LAHARZ software to model the 

potential downstream area affected by debris 

if a large landslide dam in the Río La Lima 

were to fail. The model shows that the area 

affected would be similar to the area that 

was affected by a debris flow that mobilized 

from a large landslide along the Río La 

Lima during Hurricane Mitch. The 

LAHARZ software provides a powerful tool 

for hazard scenario planning along 

drainages. 

35
IMPLICATIONS FOR LANDSLIDE 

HAZARDS 

The characteristics of rainfall-triggered 

landslides described in this report can be 

used as a partial guide to future landslide 

activity triggered by rainstorms. On the basis 

of existing data, hazardous areas include: 

moderate to steep hillslopes and less steep 

areas directly below these hillslopes, 

drainage channels downslope from landslide 

prone hillslopes, and alluvial fans at the 

mouths of drainages along mountain or hillslope fronts. Evidence for, and frequency of, 

past landslides at individual sites can be 

used to determine the level of future hazard 

(for example, see Coe and others, 2000). 

That is, one of the best indicators for future 

landslide activity is evidence of past landslide activity. For this reason, landslide 

inventory maps showing Quaternary, historic, and modern landslides are of critical 

importance. Areas susceptible to rainfalltriggered landslides are not necessarily the 

same as those susceptible to earthquake triggered landslides. The reader is referred to 

Harp and others (1981) for information on 

landslides triggered by the 1976 Mw = 7.6 

earthquake in Guatemala. 

RECOMMENDATIONS 

Attempts should be made to prevent 

development of housing and infrastructure in 

potentially hazardous areas (given in previous section). In order to specifically identify 

these areas, inventories of landslides should 

continue to be made after local and widespread rainstorms. Additionally, to the extent 

possible, physical-property information on 

colluvial soils should be compiled. As stated 

in the susceptibility section of this report, 

physical-property data can then be combined 

with DEM data to produce landslide susceptibility maps. The next step beyond susceptibility maps, would be hazard maps that 

include downslope areas that lie in landslide 

flow paths. The creation of hazard maps will 

require additional mapping of Quaternary 

and historic landslide and debris-flow 

deposits. 

For hazardous areas that are already 

inhabited, a method for predicting and delivering landslide warnings can be developed. 

One of the easiest, and most accurate ways 

to predict the timing of rainfall-triggered 

landslides, is by using a rainfall threshold. 

When such a threshold has been exceeded, or 

is expected to be exceeded by an approaching storm, a landslide warning can be issued 

for hazardous areas. The data to develop a 

preliminary rainfall threshold may already 

exist. Two thresholds should be developed, 

one for debris flows that commonly mobilize 

from shallow landslides during intense bursts 

of rainfall, and one for deep-seated landslides that are usually triggered by prolonged 

rainfall. The primary data needed to develop 

a rainfall threshold are landslide times of 

occurrence and rainfall data from a nearby 

rain gage. Also, of nearly equal importance, 

are rainfall amounts that do not trigger landslides. Because the most hazardous types of 

landslides are typically debris flows, rain 

gage data used to develop a rainfall threshold 

for debris flows (shallow landslides) should 

have at least hourly resolution. For examples 

of rainfall thresholds see reports by Caine 

(1980), Cannon (1988), and Larsen and 

Simon (1993). 

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38