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U.S. Department of the Interior 

U.S. Geological Survey

EVALUATION OF THE LANDSLIDE 

POTENTIAL IN CAPULIN CANYON 

FOLLOWING THE DOME FIRE, 

BANDELIER NATIONAL MONUMENT, 

NEW MEXICO

By Susan H. Cannon 

William L. Ellis 

Jonathan W. Godt

Open-File Report 98-42

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

Survey editorial standards and nomenclature. Any use of trade, product, or firm names is for 

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

U.S. Geological Survey 

Denver, CO 80225

1998
Contents

Abstract 1 

Introduction 2 

Landslide Descriptions 2

Boundary Peak Landslide 4

Base Camp Landslide 5 

Present Stability of Landslide Deposits 6

Global positioning system survey 6 

Soil Moisture Monitoring 7

Instrumentation 7

Soil-moisture sensor calibration 8

Instrument locations and installations 9

Results 13

Burned site response 13 

Unburned site response 18

Discussion 18

Summary and Conclusions 19 

References 21
EVALUATION OF THE LANDSLIDE POTENTIAL

IN CAPULIN CANYON

FOLLOWING THE DOME FIRE,

BANDELIER NATIONAL MONUMENT, NEW MEXICO

By Susan H. Cannon, William L. Ellis, and Jonathan W. Godt

ABSTRACT: The Dome fire burned 6684 ha in Bandelier National Monument and the adjacent Santa Fe National Forest in New Mexico. To assess the present stability of the Boundary 

Peak and Base Camp landslides in Capulin Canyon, and to evaluate the potential for a 

change in stability due to the removal of vegetation during the fire, a program of mapping and 

soil-moisture monitoring was undertaken. The Boundary Peak landslide covers an area of 

approximately 2.9 km2 , and appears to be approximately 150 meters thick, while the Base 

Camp landslide covers approximately 0.2 km2 . The thickness of the Base Camp landslide 

deposits is not known. The Boundary Peak landslide deposits experienced two areas of high 

burn intensity which cover a total area of approximately 0.15 km2 . The remainder of the 

deposits were mapped as moderate or low burn intensities. The Base Camp deposits show 

one area of low burn intensity which covers an area of 0.03 km2 .

Neither the Boundary Peak and Base Camp landslide deposits exhibit evidence of recent 

movement or instability. Both landslide deposits are mantled by the 50,000 to 60,000 yearold El Cajete pumice; deposition of the pumice appears to postdate the last movement of the 

landslides. The entire landslide topography is muted and subdued. No cracks, fissures or 

shear zones were observed, and only a few tilted trees, too few and far between to indicate 

instability of the deposits, were observed. The present-day interaction of Capulin Creek and 

the landslide toes appears to be negligible, and no danger of destabilization of the deposits by 

undercutting appears to exist at this time.

The likelihood of reactivation of the Base Camp landslide deposits due to increased infiltration 

in areas burned by the Dome fire appears to be negligible due to the small area and low 

intensity of the fire on the deposits.

Qualitative evaluation of soil-moisture data from the Boundary Peak landslide deposits indicates that (1) over time, and with continued rainfall, moisture infiltrates to greater depths at 

the burned site than at the unburned site, and (2) the soil at the burned site stays relatively 

moist throughout the summer monsoon season, while the unburned site dries out rapidly 

with the onset of warm temperatures. These differences may be due to the lack of vegetationinduced transpiration at the burned sites. Further evaluation is necessary to determine if the 

increased infiltration could potentially destabilize the landslide deposits.
INTRODUCTION

The Dome fire of May, 1996, burned 6684 ha 

in Bandelier National Monument and the 

adjacent Santa Fe National Forest in New 

Mexico. The report of the Burned Area 

Emergency Rehabilitation (BAER) team that 

evaluated conditions at the Monument immediately after the fire identified two 

Quaternary-age landslide deposits in Capulin 

Canyon as potentially unstable as a result of 

the fire, and recommended further evaluation. The larger of the two landslide deposits 

in Capulin Canyon is located on the north 

flank of Boundary Peak, while the considerably smaller deposit occurs just southwest of 

the Ranger Base Camp (fig. 1).

A potential consequence of the reactivation of 

either of these two landslide deposits is the 

creation of unstable ground that would pose 

a navigational hazard for people recreating in 

the canyon. The integrity of archeological 

sites on the deposits would be threatened 

should movement continue for any extended 

period of time. A possibility, albeit remote, 

also exists for the landslide deposits to move 

into Capulin Canyon and dam Capulin 

Creek. Should this occur, catastrophic failure of the dammed material and the resultant flooding could potentially result in 

destruction of downstream archeological 

sites, as well as the loss of human life.

To assess the current stability of these 

deposits and evaluate the potential for a 

change in stability due to the removal of vegetation, a two-phase study was initiated. The 

first phase involved both field and aerial-photographic mapping of the extent of the landslide deposits, paying particular attention to 

features that could indicate potential instability such as tilting trees and cracks or fissures. Color infra-red aerial photographs 

taken on May 5, 1996, at l:8000-scale were 

used for the mapping. The potential for 

destabilization of the landslides due to channel incision at the base of the deposits was 

also assessed by examining conditions at the 

toe of the landslide deposits in Capulin 

Canyon. Lastly, an array of survey monuments were established for a GPS-based 

movement-detection system.

The second phase of the evaluation addresses 

the issue of a potential change in stability of 

the landslide mass due to the removal of vegetation by the fire by comparing soil-moisture 

characteristics and infiltration responses to 

rainfall and snowmelt events at burned and 

unburned sites. Two soil-moisture and rainfall monitoring sites were established, one at 

a burned site on the landslide deposits, and 

the other on similar unburned terrain. At 

each site, a series of soil-moisture sensors 

are used to document the infiltration of rainfall into the soil during summer thunderstorm events. A comparison of soil-moisture 

data collected through one partial and one 

complete summer monsoon season at the 

burned and unburned sites, relative to rainfall accumulations, indicate varying infiltration characteristics of the two sites, some of 

which might be attributed to live tree transpiration rates.

This report consists of the following elements:

 Descriptions of the landslides, the observations made, and the conclusions drawn 

regarding their morphology, mode of fail 

ure, and present stability.

 Description of the GPS survey methods 

and array.

 Description of the soil-moisture monitoring 

experiment and evaluation of data collected 

through one partial and one complete summer monsoon season.

 Conclusions regarding the likelihood of 

major landslide activity in the canyon.

LANDSLIDE DESCRIPTIONS

The larger of the two landslides is located on 

the north flank of Boundary Peak and is 

referred to as the Boundary Peak landslide in 

this report (fig. 1). The other, considerably 

smaller, landslide occurs just southwest of 

the Ranger Base Camp and is called the Base 

Camp landslide (fig. 1). The landslides were 

identified by Goff and others (1990) on their 

geologic map of the area.
Capulin Creek 

Drainage Boundary

R.5E. R.6E.

1.0 0.5 0.0 1.0 kilometer

N contour interval 20 feet

Figure 1. Topographic map of portion of Capulin Canyon in Bandelier National Monument 

showing locations of Boundary Peak and Base Camp landslide deposits, burn intensity, 

instrumentation sites, GPS survey monuments, and other locations discussed in the text. 

Stippled areas dentoe area of high (H) burn intensity on the Boundary Peak landslide deposits, 

and an area of low (L) burn intensity on the Base Camp landslide deposits. Istrument site IS-1 

is within the burned area, and IS-2 is in the unburned. Filled triangles show locations of GPS 

survey monuments; open triangle (sueO) shows location of reference base station. Letter B 

marks the location of a possible basal slip surface. Letter C denotes the location of the alluvial 

fan wher 14£-dated samples were obtained. Letter D shows the location of surficial raveling of 

the landslide toe. Base is from U.S. Geological Survey Frijoles, New Mexico, 7.5' quardrangle.
Deposits from the Boundary Peak landslide, 

as outlined in Figure 1, extend a distance of 

1.2 km from the base of the headscarp to 

Capulin Canyon, and are approximately 2.4 

km wide in the canyon. Delineation of the 

landslide deposits was accomplished through 

examination of the l:8000-scale color IR aerial photographs taken on May 5, 1996, and 

field examination. The western and southwestern boundaries of the deposits were easily delineated based on topographic expression; the landslide deposits are generally 

smoother, and have gentler slopes than the 

adjacent undisturbed ground. The southeastern boundary, however, required a little 

more investigation. The 7657-foot-high peak 

located near the south margin of the landslide deposits is composed of Paliza Canyon 

Formation hornblende dacite that dips 55 

degrees to the south with a N10W strike. 

This dip is considerably greater than that 

measured for the same unit to the south (Goff 

and others, 1990), and is oriented back 

toward the headscarp, suggesting that this 

peak is not inplace material, but rather a 

back-tilted rotational block that has moved 

downslope. The southeastern boundary of 

the landslide deposits was further located by 

what might possibly be the remnants of a 

flank ridge, a feature commonly found along 

the margins of actively moving landslides 

(Fleming and Johnson, 1989). In addition, a 

contact between the Bandelier Tuff and landslide material was observed just east of this 

flank ridge, and the remnants of rotational 

slump blocks in landslide material were 

observed on the slopes below. The northeast 

margin of the deposits was delineated based 

on the topographic expression of a steep 

landslide toe in Capulin Canyon.

The headscarp of the landslide developed in 

the volcaniclastic rocks of the Cochiti 

Formation, although the landslide itself may 

have also involved the Canovas Canyon Tuffs, 

the sandstones and siltstones of the Santa Fe 

Formation, and the Paliza Canyon Formation 

hornblende dacites, all of which make up the 

flanks of Boundary Peak. The present-day 

headscarp has an average slope of 70%, 

although in places it is as steep as 86%. 

Slopes vary from 9% on the surface of the

landslide, to 50% on the steepest section of 

the toe where it rests in Capulin Canyon.

The surface of the landslide deposits is mantled by the El Cajete pumice from the 

youngest eruption of the Valles caldera about 

50- to 60 ka (Reneau and others, 1996). A 

poorly-developed soil has formed in places in 

this loose, largely unconsolidated material. 

Note that strongly water-repellent conditions, 

a phenomenon commonly described following 

intense wildfire (for example, DeBano and 

Letey, 1969; Kalendovsky and Cannon, 1997) 

were observed at only one of eleven sites on 

the deposits examined by Cannon (1997).

According to a map of burn intensity prepared by the U.S Forest Service from 

l:12,000-scale aerial photography taken after 

the fire and with limited field checking, the 

Boundary Peak landslide deposits experienced two areas of high intensity burn, both 

in stands of mature Ponderosa pine. These 

areas are shown as stippling on figure 1, and 

cover a combined area of 0.15 km2. In these 

areas all pine needles, leaf litter, and branches up to 8 cm in diameter were consumed by 

the fire. Black and gray ash and charcoal 

deposits up to 5-cm deep were observed on 

the surface. The remainder of the deposits 

were mapped by the Forest Service as 

exhibiting moderate or low burn intensities.

What appears to be a basal failure zone of 

the Boundary Peak landslide is exposed in 

the west wall of a stream cut at map location 

B (fig. 1). This zone was measured to be 84- 

cm thick, is inclined at 3 degrees to the 

north, and consists of a plastic, silty clay of 

variable color. Laboratory determination of 

the Atterburg limits obtained a liquid limit of 

61.5%, plastic limit of 41.1% and a plasticity 

index of 20.4. This material would thus be 

classified using the Unified Soil Classification 

System as a silt of high plasticity (Craig, 

1987). This possible failure surface rests on 

what appears to be red Galisteo sandstone. 

Given the location and geometry of the failure 

surface, and the slope of the headscarp, a 

possible location of the failure surface 

beneath the landslide can be inferred, as 

shown in cross-section A-A' (fig. 2). This 

reconstruction indicates that the deposits 

may be about 150 m thick. Given the impre-
2600

2400

 8 2200

I

2000

1800

Capulin 

Creek

Inferred location of 

basal slide plane

200 400 600 800 1000

Distance (m)

1200 1400 1600

Figure 2. Cross section through Boundary Peak landslide deposits. Topography is from 

U.S. Geological Survey Frijoles 7.5' quadrangle.

else values for the width and length of the 

deposits, a volume of the landslide deposits of 

approximately 530,000,000 m3 is calculated.

Movement of the Boundary Peak landslide 

likely occurred along a deep-seated, convexupward failure surface, which resulted in a 

rotational transfer of material downslope and 

out onto the valley floor. Material did not 

travel down Capulin Canyon for any distance. 

The topography of the landslide suggests that 

it moved primarily as one unit, although it 

appears that the main rotational block broke 

into a number of smaller, nested blocks at its 

lateral margins, resulting in a stepped topography on either side of the main block. No 

sedimentologic or geomorphic evidence was 

observed upstream from the landslide deposit 

that would indicate that the landslide ever 

dammed Capulin Creek, suggesting that the 

rates of movement into Capulin Creek were 

sufficiently slow to allow the creek to maintain a channel.

An alluvial fan is located on the southeast 

margin of the landslide deposits; its outline is 

shown on figure 1. This fan consists of fluvially reworked landslide material, as well as 

material eroded from the headscarp. The fan 

surface is covered with abundant open-work 

boulder and cobble berms. The materials 

that make up these berms are often imbricated, indicating a surface-water transport

mechanism, and the berms themselves lack 

the matrix material necessary to identify 

them as debris-flow deposits. In addition to 

the fan surfaces, boulder berms have been 

deposited where drainages off the headscarp 

intersect the landslide deposits.

Incision into the fan surface at map location 

C by recent surface flows revealed a stratigraphy that indicates that fires have occurred 

on or near the landslide deposits in the past. 

The surface of the fan is blanketed with 

approximately 2.5 cm of ash and charcoal 

from the Dome fire. Beneath this, exposed in 

a 2.50-m-high cut, are two sequences of primarily water-lain sediments capped with thin 

layers that contain abundant ash and charcoal fragments. These ash- and charcoalrich units are interpreted as slack-water 

deposits associated with runoff events following fires located upslope in the drainage. The 

i 4C dates of A.D. 1650-1950 and A.D. 1280- 

1630 were obtained from charcoal in the 

upper, and lower soils, respectively. We did 

not see any evidence of landslide response to 

these past fires.

Base Camp Landslide

The Base Camp landslide deposits, as outlined in figure 1, extend 0.5 km from the 

headscarp to the canyon, and are O.4 km
wide at their broadest point. The landslide 

appears to have formed in the Upper 

Bandelier Tuff. The arcuate headscarp is as 

steep as 85%, and the toe of the landslide 

also rests in Capulin Canyon, with a slope of 

53%. This landslide also failed as a single 

rotational unit that left deposits on the hillside and in the canyon. Material did not 

travel down Capulin Canyon. No sedimentological evidence was observed upstream from 

the landslide deposit that would indicate that 

the landslide ever dammed Capulin Creek, 

suggesting that the rates of movement into 

Capulin Creek were sufficiently slow to allow 

the creek to maintain a channel. 

One area of low burn intensity that covers 

approximately 0.03 km2 , or one-sixth, of the 

deposits is shown on the U.S. Forest Service 

map of fire intensity (fig.l).

PRESENT STABILITY OP LANDSLIDE DEPOSITS

Both the Boundary Peak and Base Camp 

landslide deposits are mantled the El Cajete 

pumice; geochronologic data suggests an age 

of about 50 to 60 ka for this deposit (Reneau 

and others, 1996). The superposition of the 

pumice on the landslide deposits indicates a 

minimum age of 50,000 to 60,000 years for 

the last significant movement of the landslides. The entire landslide topography is 

muted and subdued, also indicating an 

advanced age, and lack of recent movement. 

We observed no cracks, fissures, or shear 

zones, or any other signs of instability on the 

landslide deposits. Although the thickness of 

the pumice mantle on the landslide deposits 

is unknown, the weathering of the pumice 

and degree of soil development is sufficient 

such that reactivation of the underlying landslide deposits could be reflected at the surface. Although our proposal suggested 

installing photographic-monitoring sites on 

the landslide deposits, this lack of evidence of 

active movement or unstable ground made it 

impossible to select sites for monitoring that 

would give informative results.

A few tilted trees were observed on the landslide deposits but they are too few and far 

between to indicate instability. The tilting of 

the few trees we observed can be explained as 

a phototropic response (Pfripps, 1974), and a

grouping of contiguous, similarly-aged tilted 

trees is necessary to indicate landslide instability.

The interaction of Capulin Creek and the 

toes of the landslides appears to be negligible, and no danger of destabilization-of the 

deposits by incision appears to exist at this 

time. The stream bed of the creek in 

Capulin Canyon is quite broad and flat, and 

is not constricted by either of the landslide 

toes at this time. At one location (map location D) the steep front of the Boundary Peak 

landslide toe has failed as a surficial slip. 

The approximately 1-m-high scarp is subtle 

and smoothed by erosion, indicating that 

this is not a recent feature. The slip is 

approximately 15-m wide and 3-m high. The 

recent flooding on Capulin Creek has, however, incised slightly into this raveling; surface, resulting in a 2-m- high cut into the 

channel bank. This was the only interaction 

of Capulin Creek with the either of the toes 

of the landslides observed in the canyon bottom, and its scale precludes any threat of 

destabilization of the landslide mass.

Global Positioning System Survey

A network of survey monuments was 

installed on the landslide deposits in July of 

1997 for a GPS-based movement-detection 

system. Locations of the monuments are 

shown as triangles in figure 1. The 1997 

GPS survey was made using three Ashtech 

Z-12 dual-frequency receivers and rapid-static survey technique which involves ten to 

thirty minute site occupations. The data 

were reduced using Ashtech's PNAV software 

(v. 2.4.0M) with forward processing running 

under DOS on a notebook PC. Processing 

for the survey array used the reference base 

station -labeled sueO on figure 1. Control 

was established using static survey techniques between a known Cooperative Base 

Network Control Station located at Technical 

Area 33, Los Alamos National Laboratory 

(National Geodetic Survey point F01671, Los 

Alamos National Laboratory survey marker 

1709 5-62). Relative positional accuracy of 

the survey monuments should be on the 

order of O.O2 m in the horizontal and O.03 m 

in the vertical.
Only one survey of the array has been completed; repeated surveys will be necessary to 

determine and monitor movement of the 

landslide deposits.

SOIL-MOISTURE MONITORING

This phase of the evaluation addresses the 

issue of a potential change in stability of the 

landslide mass due to the removal of vegetation. This analysis is based on the assumption that the only variable altered by the fire 

that affects the stability of the landslides is 

the infiltration of rainfall and snowmelt into 

the slide mass at the surface. Presumably, 

any other deep water source and the internal 

hydrologic characteristics of the mass were 

not altered by the fire. Two possible effects 

of the fire are: (1) a change in infiltration 

rates and amounts of rainfall and snowmelt 

as a result of removal of the mulching litter 

on the ground surface; and (2) a change in 

the rates and amounts of rainfall that can 

infiltrate to depth because of the decreased 

transpiration rates of the burned trees. To 

address these issues, two soil-moisture monitoring sites were established, one on the 

burned slide mass, and the other on similar 

unburned terrain. Each site consists of a 

tipping bucket rain gage and two sets of four 

soil-moisture sensors installed to determine 

negative soil pore-water pressures, that is, 

soil tensions, at varying depths. This configuration was designed to document the infiltration of rainfall into the soil during summer 

thunderstorm events.

Soil tension is a measure of the forces holding soil moisture to the soil structure. When 

the soil is very dry,, the small amount of 

inter-particle water in the voids is bound 

tightly to the soil particles. As the inter-particle voids in the soil are filled with moisture, 

the overall forces binding the moisture to the 

grains is lessened. Thus, in the simplest 

sense, lower soil tension values indicate a 

higher moisture content. Note, however, that 

the relation between soil tension and volumetric water content for silt and fine sand is 

not linear, but rather resembles a flattened-S 

shaped curve, as determined experimentally 

and shown in figure 3. The form and position of the curve depends on the grain-size

distribution of the soil, or better yet, the poresize distribution (Burdine, 1953). As represented by the tails of the S-shaped curves, 

the change in volumetric water content 

becomes negligible at varying values of soil 

tension, depending on the materials. 

Although the form of this moisture-retention 

curve is unknown for the materials at the 

instrument sites without further testing, 

grain-size analyses of the site materials indicates a silty sand to sandy gravel texture. 

For such> materials, the change in volumetric 

water content can be considered to be negligible for soil-tension values less than -50 kPa.

Instrumentation

Watermark model 200SS soil-moisture sensors, manufactured by Irrometer Company, 

Inc. of Riverside California, were selected for 

monitoring soil-pore water tension conditions 

at each site. The sensors consist of two concentric electrodes embedded in a granular 

matrix which has a consistency similar to fine 

sand. Included in the matrix is a gypsum 

block which minimizes any effects of soil 

salinity on electrical conductivity. These 

granular-matrix sensors were developed in 

the early 1980's, and have been used extensively in the agricultural industry for irrigation monitoring and control.

For purposes of this investigation, the granular-matrix sensors offer several advantages 

over other possible soil-moisture instrumentation. The cylindrical sensors, having 

dimensions of 2.25 cm in diameter and 8 cm 

in length, are easily installed in small-diameter hand-augered holes at various depths in 

the ground with a minimal disturbance of the 

existing soil column. Careful backfilling and 

tamping of the emplacement hole minimizes 

the possibility that it may provide an avenue 

of increased permeability for surface water to 

migrate to the sensors, although this possibility cannot be eliminated entirely. Other 

methods, such as TDK (time-domain reflectometry) or gypsum block sensors, would 

require greater disturbance of the overlying 

and surrounding soil column for emplacements of the sensing elements, and minimal 

disturbance of the natural soil column was 

considered to be a critical concern for this
study. Further, the granular-matrix sensors 

can be placed in the ground for long periods 

of operation (even freezing) with no maintenance, and the cost is low relative to other 

instruments.

Additional instrumentation at each of the 

sites includes a tipping bucket rain gage 

capable of measuring rainfall in increments 

of 0.25 mm (0.01 in.), and soil-temperature 

sensors with an accuracy of ±1 °C installed 

at 15 cm and 61 cm depths. The soil-temperature sensors were installed to provide 

-temperature correction in converting soil-sensor output to soil-tension values.

Data from the rain gages, soil-moisture sensors, and temperature sensors at each site 

are monitored and recorded by a datalogger/cellular telemetry system marketed by 

Environmental Cellular Inc. of Boulder, 

Colorado. The data recording and acquisition 

systems allow for data retrieval by remote 

computer dial-in. As currently configured, 

the systems record rainfall totals for six hour 

intervals, and the soil-moisture and temperature readings every six hours. In the event of 

accumulated rainfall that exceeds 2.5 mm 

(0.1 in.) in any 6 hour recording interval, the 

systems switch to a fast-record mode wherein 

rainfall totals, soil moisture, and temperature 

readings are recorded every 15 minutes for 

the following 6 hours. The systems then 

return to the slow-record mode. This configuration allows for the rapid recording of soilmoisture conditions during significant rainfall events, and results in the savings of significant data storage space.

Soil-Moisture Sensor Calibration

The granular-matrix soil-moisture sensors 

provide an indirect measure of soil-water tension, and thus a series of calibrations are 

necessary to convert the sensor output to 

soil-tension values as a function of temperature.

Comprehensive research into the calibrationof the Watermark sensors has been done at 

:the Malheur Experimental Station which is 

operated by Oregon State University at 

Ontario, Oregon. Here, the Watermark sensors have been tested in both lab and field 

environments (for example, Eldredge and others, 1993; Shock and Barnum, 1992; Stieber 

and Shock, 1995). The field calibration of 

Watermark sensors determined by Eldredge 

and others (1993) is based on a comparison 

of sensor output to tensiometer readings, and 

produced a linear relationship between sensor output and soil tension. This relation is 

defined in the range between 0 to -80 kPa for 

79 data points with an r2 of 0.89. The relationship of soil tension to sensor output 

derived by Eldrege and others (1993) is:

= -6.44 -0.738* eqn. 1

where \|/ is soil-water tension in negative kPa 

and x is the reading obtained with the 

30KTCD meter supplied by the manufacturer 

for reading the sensor output. The 30KTCD 

meter is designed such that the meter readings are related to sensor resistance and temperature by the equation:

#-05

0.1759(1-0.0137) eqn. 2

where R is resistance in kQ, and Tis temperature in °C. By substitution of equation 2 

into equation 1, the relation between soilwater tension and sensor resistance and temperature is:

\j;= -6.44-

(1-0.0137) eqn. 3

Interface circuitry to convert a 12v DC power 

source to provide 5v AC excitation voltage to 

the soil-moisture sensors was built by the 

datalogger supplier. Because the sensors are 

an electrical resistive device, it is necessary 

to calibrate the sensors and interface circuitry to the datalogger output. To accomplish 

this calibration known resistances were 

applied to each analog input and the corresponding datalogger output in analog-to-digital counts recorded. This calibration resulted 

in a nonlinear relationship of the form:

0.0188C2 +11288C 

100O (r2 = 0.98) eqn. 4

where R is resistance in kQ and C is datalogger output in counts. Substitution of equation 4 into equation 3 provides the following

8
relationship for soil-water tension (in negative kPa) as a function of datalogger output 

and temperature:

-434 + O.OS4T - 790 x 10"5 C2 - 0.047C

1-0.0137

eqn. 5

Note that although the Watermark sensors 

can respond to soil tensions well beyond the 

range of the data used in the calibration 

(between 0 and -80 kPa), it would not be 

appropriate to extrapolate the curves to these 

higher tension values. For this reason, only 

data in the range of O to -80 kPa are considered in this study. This constraint poses no 

serious limitations as soil tensions in excess 

of -50 kPa are measured in soils that can 

experience very little changes in water content (fig. 3).

And lastly, in order to quantify the soil-moisture response, or to convert soil-tension values to volumetric water contents and permeabilities, further testing is necessary to 

establish the soil-moisture retention curves 

for the site materials (for example, 

vanGenuchten, 1980; Brooks and Corey, 

1966). Further complicating the issue of 

determining volumetric water contents from 

soil tension values, repeated wetting and drying cycles experienced by the soil result in a 

hysteresis in the soil water retention curve.

day

Silt

0.8

0.6 C

6

-80 -60 -40

Soil Tension, kPa

-20

0.2 O

0.0

Figure 3. Soil water retention curves for 

clay, silt, and fine sand.

Laboratory testing of soil permeability characteritics may be necessary to quantify this 

relation for the situation on the landslide 

deposits.

Instrument Locations and 

Installations

The location of the two soil-moisture monitoring sites (IS-1 and IS-2) on the Boundary 

Peak landslide deposit are shown in figure 1. 

Site IS-1 is located in an area that experienced a high burn intensity, and as a result 

is very open and exposed to sunlight. The 

surface is mantled by an unknown thickness 

of the El Cajete pumice. The ground surface 

at site IS-1 slopes 3 degrees to the northeast, 

and the character of the subsurface materials 

was examined by digging a shallow pit and 

by augering with a 6.35 cm auger bit to a 

depth of 122 cm. The following materials 

and characteritics were revealed:

Site IS-1:

(in centimeters)

0-4 dry ash, charcoal and pumice frag

ments 

4-8 dry, light tan silty sand with

pumice fragments 

8-30 moist, light brown silty sand with

pumice fragments 

30-61 slightly moist, light brown silty

sand with pumice fragments 

61-86 slightly moist, light tan silty sand

with pumice fragments 

86-122 dry, white ignimbrite interbed

The fire intensity map prepared by the U.S. 

Forest Service shows the location of Site IS-2 

in a moderately burned area. Field evidence, 

however, indicates that fire swept through 

the area, but with a very low temperatures 

and a short residence time; some ponderosa 

pine trunks are singed to a height of 91 cm, 

but the needles remain green, the bark is 

healthy, and old pine needles remain on the 

ground. We thus consider this an essentially 

unburned site. Site IS-2 is considerably 

shadier than IS-1 due to the presence of 

abundant living ponderosa pine. The ground 

surface slopes 3.5 degrees to the northnortheast, and although it is also mantled 

with El Cajete pumice, some cobbles and
Table 1. Soil-moisture sensor number and installation depth information at sites JS-1 

and IS-2. Soil temperature sensors at each site are installed at depths of 15 

 and GO cm.

small boulders derived from the headscarp 

are scattered on the ground surface. The 

subsurface materials were examined by 

augering to a depth of 91 cm. The following 

materials and characteristics were described:

:Site IS-2:

(in centimeters)

0-15 dry, light tan silt

15-38 moist, light brown silty clay with

pumice fragments 

38-53 moist, lightly oxidized, light brown

silty sand with pumice fragments 

53-91 dry, light tan silty sand with some

white ignimbrite fragments

It was more difficult to remove material from 

the auger tip at this site than at IS-1, presumably due to a slightly higher clay content 

of the materials. Grain-size distribution testing is presently underway to quantify the 

differences between the two sites.

Note that strongly water-repellent conditions, 

a phenomenon commonly described following 

intense wildfire for example, DeBano and 

Letey, 1969; Kalendovsky and Cannon, 1997) 

were not observed at either of the instrumentation sites.

Figures 4A and 4B are sketch maps showing 

 the location of the soil-moisture sensor 

emplacement holes, temperature sensor 

emplacement holes, rain gages, dataloggers, 

and solar panels at each instrumentation 

site. The depths of installation of the soilmoisture sensors at each site are listed in 

table 1. The depth to which the deepest sensors were installed was controlled by the 

presence of unweathered pumice. Note also 

that sensors 5 through 8 at site IS-2 are not 

in the same sensor number-depth sequence 

as the other array due to installation constraints.

The raingages and soil-monitoring instrumentation were installed in late August of 1996 

and have operated nearly continuously since 

that time. Soil-temperature sensors were 

installed in early September of 1996 allowing 

calculation of soil-tension values. Note that 

the temperature sensors were installed at 

depths of 15 and 61 cm. Temperature data 

from the sensor at 15 cm was used in the 

calibration of soil-moisture sensors at 15 cm, 

and the temperature probe at 61 cm was 

used for all other soil-moisture sensors. 

Except for an approximately two-week period 

in late October and early November of 1996 

during which solar power problems were 

encountered at IS-2, and a 1-week period in 

September of 1997 when the site was vandalized, essentially continuous records of rainfall 

and snowmelt events and soil-moisture conditions have been recorded at both sites.

Note that the soil-moisture sensors are 

installed in the ground wet and surrounded 

by a slurry of the soil in which they are 

installed. The slurry insures that air pockets 

are eliminated so that good contact between 

the soil and sensor is established. Some 

period of time is therefore required for the 

natural soil-moisture conditions in the proximity of the sensors to return to equilibrium, 

the length of which depends on the water

10
N

Scale: 1cm =0.60 m

Solar panel

Burned log

Data 

logger

Rain gage

Soil moisture sensors

Tree

2 O

Auger sample holes

Figure 4A. Map of instrument installation IS-1 (burned site).

11
Tree with 

solar panels

Battery and case

Soil moisture sensors

O O

o

Auger sample holes

N

Scale: 1cm = 0.60 m

Rain gage

Figure 4B. Map of instrument installation IS-2 (unburned site).

12
content and properties of the surrounding 

soil. The soil surrounding the sensors was 

considerably drier than the installation slurry and thus a period of drying was expected 

following sensor installation.

Results

A qualitative comparison of the soil-tension 

responses of the burned and unburned sites 

(figs. 5 and 6, respectively), recorded from 

September 10 to November 30, 1996, and 

from December 30, 1996 to December 30, 

1997 (figs. A and B, respectively) indicates 

relations somewhat different than those 

described in Cannon and Ellis (1997), which 

were based on interpretation of the response 

to three discrete rainfall events following the 

summer monsoon season. The comparison 

presented below yields two primary relations: 

(1) over time, and with continued rainfall, 

moisture infiltrates to greater depths at the 

burned site than at the unburned site, and 

2) even though the burned site is very open 

and exposed to direct sunlight, the soil at 

this site stays relatively moist throughout the 

summer monsoon season, while the more 

shaded unburned site dries out rapidly with 

the onset of warm temperatures.

The rainfall records for 1996 and 1997 show 

similar rainfall accumulations at both of the 

two sites (figs. 5A and B, 6A and B). 

Following the installation of the instruments 

in late August of 1996, three primary periods 

of rainfall accumulation were recorded: one 

in mid-September (from the 12th through the 

19th), another in early October (on the 4th 

and 5th), and lastly, one in late October 

(from the 23rd through the 29th). The rainfall record for 1997 also included the summer monsoon season. A number of small 

storms occurred between early February and 

late June, followed by a relatively dry period 

until mid-July. Rain then fell nearly continuously until late August. Similar to the 1996 

season, three discrete rainfall events then 

occurred; these being in early September 

(from the 6th through the 10th), late 

September 9 (from the 20th through the 

22nd), and in mid-November (from the 10th 

through the 17th). The following describes 

the response of the soil-moisture sensors at 

the burned and unburned sites to this rainfall record.

Burned Site Response: The record for 1996, 

as shown in figure 5A, reflects a gradual 

movement of soil moisture to greater depths 

with a continued application of rainfall. In 

response to the second period of rainfall 

(starting on September 14th) during the 

September event, both of the 15 cm sensors 

show a rapid wetting, which was then followed by a period of gradual drying. The 

remaining sensors either continued to dry, or 

did not respond. The October 4-5 event was 

characterized by an immediate wetting of 

both the 15 cm sensors, followed about 12 

hours later by sensor ST-7 at 60 cm. Again, 

this response was followed by a gradual drying, and the remaining sensors continued to 

dry or did not respond. The October 23-29 

rainfall and snowmelt event showed an 

immediate wetting of the two 15 cm sensors, 

followed about 4 days later by wetting of sensor ST-7 at 60 cm, which was followed one 

day later by sensor ST-3 at 60 cm, and lastly, two days later, by the 84 cm sensor. The 

remaining sensors showed no response.

The soil-moisture data for 1997, shown in 

Figure 5B, also reflects a gradual infiltration 

of soil moisture to depth with the continued 

application of rainfall. From the start of the 

record until early March, the record is characterized by the drying and wetting of both 

the 15 cm sensors that accompanied freezing 

and thawing of the upper soil surface. The 

deeper sensors did not show this effect. 

Then, starting in mid-March and continuing 

until late June, both 15 cm sensors showed 

immediate wetting at the onset of each small 

rainfall event, followed by a more gradual 

period of drying. Sensor ST-6 at 30 cm 

remained constant through this period, and 

the other was extremely dry. Of the 60 cm 

sensors, ST-7 remained constant, while ST-3 

showed a wetting response in late April. 

Oddly, although neither of the 30 cm sensors 

registered any effects of these rainfall events, 

the 79 cm sensor does show a wetting 

response. There are two possible explanations for this phenomenon: either the wiring 

was switched during installation and the 

channel thought to be reading the 79 cm 

sensor is actually reading the 30 cm sensor, 

or an inter-soil channel is directing moisture 

to this deeper sensor. This issue can possibly be resolved when the sensors are 

removed from the ground. Continuing on,

13
80 T

70 --60 --

50 --

30 --

20 --

10 --

ST1@15cmST2@30cm

ST3@60cm ST4@79cm

ST5@15cm

ST6@30cm

ST7@60cm

 -ST8@84cm

cum. precip. (mm)

rainiall and/or snowmelt events

Date

Figure 5A. Plot of cumulative precipitation and soil-tension measurements with time for IS-1 (burned site) in 1996. ST refers 

to soil-moisture sensors. Cumulative precipitation totals do not include events that occurred between August 29 and 

September 10,1996. 13.55 mm of rainfall was measured at IS-2 between those dates.
600

ST1@15cm ST2@30cm 

ST3@60cm ST4@79cm ST5@15cm 

ST6@30cm ST7@60cm ST8@84cm 

cum. precip. (mm)

JU> l-^^^Uva/rtyJifftfJlA.'i '*'»*»"

Date

Figure 5B. Plot of cumulative precipitation and soil-tension measurements with time for IS-1 (burned site) in 1997. 

ST refers to soil-tension sensors.
80

70 --60 --50--

30 --

20

10 -- ST1@15cm ST2@30cm ST3@60cm ST4@71cm ST5@30cm ST6@60cm ST7@15cm ST8@ 100cm cum. precip. (mm) I rainfall and/or snowrnelt events ^yV yijwT' " /

200

- 180-- 160-- 140 ^

E, 

120 £100 g

-- 80

60

--40

--20

I 

| o

$c-

§ § £2 35 55

$ $ CO

1

COo>

SJ

Date

Figure 6A. Plot of cumulative precipitation and soil-tension measurements with time for IS-2 (unburned site) in 1996. ST 

refers to soil-moisture sensors. Cumulative precipitation totals do not include events that occurred between October 20 and 

November 8,1996. A total of 67.5 mm of rainfall was measured at IS-1 during this time.
600

ST1@15cm 

ST2@30cm ST3@60cm ST4@71cm ST5@30cm ST6@60cm ST7@15cm

-- ST8® 100cm "" cum. precip. (mm)

Date

Figure 6B. Plot of cumulative precipitation and soil-tension measurements with time for IS-2 (unburned site) in 1997. ST refers 

to soil-moisture sensors. Data was not collected for a week in early September. Further, in late September, a rainfall 

accumulation of about 60 mm was measured at IS-1 which was not recorded at this site.
during the dry period between late June and 

mid-July, the two 15 cm sensors and the 

presummed-79 cm sensor, followed by sensor 

ST-6 at 30 cm, show a gradual drying. The 

onset of the rainy period in mid-July is 

accompanied by an immediate wetting of 

both 15 cm sensors, which then continue to 

gradually dry and then wet up in response to 

lulls and periods of rainfall accumulation. 

Sensor ST-6 at 30 cm showed a gradual drying during this period, followed by a constant 

value. The dry period between late August 

and early September shows a gradual drying 

of the sensors that had wetted during the 

preceding rainy period. The September 6-10 

storm resulted in the re-wetting of both the 

15 cm sensors, but no response of the deeper 

sensors. Even the errant 79 cm sensor did 

not register this event. However, the 

September 20-22 storm resulted in an immediate wetting of both 15 cm sensors, sensor 

ST-6 at 30 cm, both 60 cm sensors, and the 

79 cm sensor. This was again followed by a 

period of gradual drying until the final: storm 

of the season in mid-November. Both the 

15cm sensors responded immediately to this 

event, followed a few days later by sensor ST3 at 60 cm and a little later still, by sensor 

ST-6 at 30 cm.

The drying responses of the sensors 

described above also reflect an important 

characteristic of the burned site. Although 

the sensors show a gradual drying between 

rainfall events, the minimum values of soilwater tension attained are, in general, 

around -15 kPa. This fact that this minimum value is small relative to those measured at the unburned site (described below), 

indicates that this site remains relatively 

moist throughout the summer. This is a particularly interesting result given that the 

burned site is relatively open and exposed to 

direct sunlight, while the unburned site is 

well shaded.

Unburned Site Response: Data from the 

soil-moisture sensors through 1996, shown 

in figure 6A, illustrate a response to rainfall 

events quite different from that of the burned 

site. During the second period of rainfall 

within the September 12-19 event, sensor 

ST-7 at 15 cm showed a relatively rapid wetting. A period of gradual drying was then

ended by a rather gradual wetting of both the 

15 cm sensors and sensor ST-5 at 30 cm in 

response to the early October rainfall. A gap 

in the data exists due to power difficulties in 

mid-October. However, when data acquisition resumed, both 15 cm sensors and sensor ST-5 at 30 cm were relatively moist. 

The soil-moisture data for the unburned site 

from 1997, shown in figure 6B, show a 

response remarkably different from that of 

the burned site. The record again shows a 

response to repeated freezing and thawing by 

both 15 cm sensors from the start of the 

record to mid-March. The two 30 cm sensors 

did not respond to this effect, and the 

remaining sensors are so dry as to be off the 

vertical axis. As with the burned site, both 

15 cm sensors show a rapid wetting followed 

-by a more gradual drying response to rainfall 

starting in mid-March. In contrast with the 

burned site, however, both 30 cm sensors 

also show this response, although it is less 

rapid and uniform than is that of the 15 cm 

sensors. More importantly, however, and 

again in contrast with the burned site, at the 

end of April all four sensors start to dry out 

quickly and stay dry for the rest of the summer (with the brief exception of dramatic 

responses to rainfall events in late September 

and mid-November). Values for soil-water 

tension are considerably drier than the average value of -15 kPa measured at the burned 

site.

Discussion

The comparison of the soil-moisture response 

to rainfall between the burned and unburned 

sites presented here yields two primary relations: (1) over time, and with continued rainfall, moisture infiltrates to greater depths at 

the burned site than at the unburned site, 

and (2) the soil at the burned site stays relatively moist throughout the summer monsoon 

season, while the unburned site dries out 

rapidly with the onset of warm summer temperatures. Given that the burned site is relatively open and exposed to direct sunlight, 

while the unburned site is rather shaded, 

these pronounced differences may indicate 

that transpiration by the living Ponderosa 

pine at the unburned site plays a considerable role in removing moisture from the soil

18
during the summer months. As 60% of the 

annual precipitation falls between June and 

September (Alien, 1989), this effect may have 

a considerable consequence on the soil-moisture budget of the landslide deposits. Note, 

-however, that further evaluation is necessary 

to determine if the increased infiltration is 

are sufficient to result in the destabilization 

of the landslide deposits.

These findings contrast with those of 

Zwolinski (1971) and Campbell and others 

(1977), who examined the influence of fire on 

water infiltration capacities in Ponderosa 

pine ecosystems in Arizona. Both papers 

concluded that infiltration capacities 

decreased significantly following severe 

burns, and attributed this decrease to the 

possible presence of water-repellent soils. 

(Water-repellent soils were not detected at 

either of the two sites used in this study.) 

Zwolinski (1971) describes infiltration capacities restored to nearly -normal conditions 

after one winter, while the data presented 

here illustrates a considerable disparity 

between infiltration characteritics of the 

burned and unburned sites well after one 

winter.

SUMMARY AND CONCLUSIONS

To assess the present stability of the 

Boundary Peak and Base Camp landslides in 

Capulin Canyon, and to evaluate the potential for destabilization due to the removal of 

vegetation during the Dome fire, a program 

of mapping and soil moisture monitoring was 

undertaken.

The Boundary Peak landslide covers an area 

of approximately 2.9 km2, and appears to be 

approximately 150 m thick, while the Base 

Camp landslide covers approximately 

0.2km2 . The thickness of the Base Camp 

landslide deposits is not known. The 

Boundary Peak landslide deposits experienced two areas of high burn intensity which 

cover a total area of approximately 0.15 km2 . 

The remainder of the deposits were mapped 

as moderate or low burn intensities. The 

Base Camp deposits show one area of low 

burn intensity which covers an area of 0.03

km2 . Initial emplacement of both the 

Boundary Peak and Base Camp landslide 

deposits occurred along deep-seated, convexupward failure surfaces, which resulted in a 

rotational transfer of material downslope and 

out onto the valley floor. Material from either 

landslide did not travel down Capulin 

Canyon for any distance. No sedimentological evidence was observed upstream from the 

landslide deposits that would indicate that 

the landslides ever dammed Capulin Creek, 

suggesting that the rates of movement into 

Capulin Creek Were sufficiently slow to allow 

the creek to maintain a channel.

Neither the Boundary Peak or the Base 

Camp landslide deposits exhibit evidence of 

recent movement or instability. Both landslide deposits are mantled by the El Cajete 

pumice, giving a minimum age of 50,000 to 

60,000 years for the latest significant movement of the landslides. The entire landslide 

topography is muted and subdued, no 

cracks, fissures or shear zones were 

observed, and only a few tilted trees, too few 

and far between to indicate instability of the 

deposits, were observed. Although the thickness of the pumice mantle on the landslide 

deposits is unknown, the weathering of the 

pumice and degree of soil development is sufficient such that reactivation of the underlying landslide deposits could be reflected at 

the surface. The interaction of Capulin 

Creek and the landslide toes appears to be 

negligible, and no danger of destabilization of 

the deposits by undercutting appears to exist 

at this time.

The likelihood of reactivation of the Base 

Camp landslide deposits due to increased 

infiltration in areas burned by the Dome fire 

appears to be negligible due to the small area 

and low intensity of the fire on the deposits.

Qualitative evaluation of the soil-moisture 

data from the Boundary Peak landslide 

deposits indicates an increase in rainfall and 

snowmelt infiltration at the burned site, suggesting that removal of vegetation by the 

Dome fire could possibly affect the stability 

of the deposits. The evaluation indicates 

that (1) over time, and with continued rainfall, moisture infiltrates to greater depths at 

the burned site than at the unburned site, 

and (2) the soil at the burned site stays rela19
lively moist throughout the summer monsoon season, while the unburned site dries 

out rapidly with the onset of warm temperatures. These differences appear to be due to 

the lack of vegetation-induced transpiration 

at the burned site.

Further evaluation is necessary to determine 

if the increased infiltration is sufficient to 

result in the destabilization of the landslide 

deposits. Movement on this type of deepseated landslides is precipitated by infiltration of water deep into the deposits. Either 

a number of consecutive, very wet rainfall 

seasons, a single large snowmelt event, or 

any combination of these effects, would be 

necessary to generate this condition.

The most likely potential consequence of the 

reactivation of this landslide deposit would 

be the creation of unstable ground that 

would pose a navigational hazard for hikers 

on the deposits themselves. The integrity of 

archeological sites on the deposits would be 

threatened should movement continue for 

any extended period of time. The remote 

possibility also exists for the landslide 

deposits to move into Capulin Canyon and 

dam Capulin Creek, although there is no 

evidence to indicate that this occurred in the 

past. Should this occur, catastrophic failure 

of the dammed material and the resultant 

"flooding could result in destruction of downstream archeological sites, as well as the 

loss of human life.

The likelihood of reactivation of these 

deposits appears to be so slight at this time 

that no restrictions of access to Capulin 

Canyon due to this threat appears to be necessary.

Most importantly, a general awareness of the 

state of the landslide deposits by those working in the canyon can be extremely useful in 

evaluating their continued stability:

 The steep section of the landslide toe in 

Capulin Canyon (between points B and D 

on Figure 1) should be monitored for signs 

of steepening or erosion by the creek.

 Formation of cracks and shears within the 

deposits, particularly in the areas of 

stepped topography on the lateral margins 

of the primary block could indicate reactivation.

 The presence of new seeps or springs, or 

increased flow in existing seeps or springs 

along the toe of the landslide deposits in 

Capulin Creek or at the heads of channels 

on the deposits, could indicate increased 

groundwater flow through the deposits in 

response to increased infiltration into the 

burned area.

 The development of areas with numerous 

tilted trees should be noted.

Should these conditions arise, access restrictions should be considered for Capulin Creek 

downstream from the landslide deposits.

And finally, in light of the predictions of higher than average snow and rainfall accumulations in the southwest in response to the 

1997-98 El Nino event, we recommend continuing monitoring of soil-moisture conditions 

on the Boundary Peak landslide, as well as a 

repeat GPS survey of the established monument array.

20
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21