Temperature, Snowmelt, and the Onset of Spring Season 

Landslides in the Central Rocky Mountains 

Open-File Report 1997-027


U.S. Department of the Interior 

U.S. Geological Survey 
U.S. DEPARTMENT OF THE INTERIOR 

U.S. GEOLOGICAL SURVEY 

Temperature, Snowmelt, and the Onset of Spring Season 

Landslides in the Central Rocky Mountains 

by 

Alan F. Chleborad1 

Open-File Report 97-27 

This report has not been reviewed for conformity with U.S. Geological Survey 

editorial standards and stratigraphic nomenclature. Any use of trade or company 

names is for descriptive purposes only and does not imply endorsement by the 

U.S. Geological Survey.

1Denver, Colorado 

ABSTRACT 

Snow meltwater (snowmelt) that seeps into the subsurface is a 

major factor contributing to the development of landslides during 

the spring in mountainous areas of the Rocky Mountain region. An 

examination of historical temperature data in relation to spring 

season landslide occurrences reveals an association between the 

landslide events and intervals of rising temperatures that accelerate 

the production of snow meltwater. Historical climatic data 

recorded at local weather stations located near the landslide sites 

are used to show the association and to identify a temperature 

threshold that may be useful for forecasting the onset of spring 

season landslides. Historical daily temperature maximums and 

minimums for unmonitored landslide sites are estimated by 

applying an elevation correction factor to historical temperature 

data from nearby weather stations. The proposed temperature 
threshold (a 6-day moving average of daily maximum temperature 

of 58° F) is defined by the number and temporal distribution of 

snowmelt related landslide events. The results of the study suggest 

that real-time temperature data recorded at weather stations 

throughout the Rocky Mountain region is potentially a valuable 

source of information that may be useful for forecasting the onset 

of spring season landslides. 

INTRODUCTION 

Landslides triggered by snowmelt or a combination of snowmelt 

and rainfall are common during the spring in many mountainous 

areas of the Rocky Mountain region. Spring season landslides, 

especially debris flows (often referred to as "mudslides" in media 

news reports), are numerous in years with unusually heavy 

snowfall and associated deep snowpack. However, few details are 

known of the sequence, time, intensity, or duration of antecedent 

climatic conditions that trigger the slope failures. Such information 

may be useful for mitigation of landslide hazards and for 

forecasting the occurrence of landslides. 

For many years, climatic data, including daily temperature 

maximum and minimums and precipitation, have been collected at 

numerous local weather stations (weather observing sites) 

supervised by the National Oceanic and Atmospheric 

Administration (NOAA)/National Weather Service. I undertook 

this study to investigate the usefulness of this source of historical 

climatic data for identifying associations between antecedent 

climatic conditions and the onset of spring season landslides in 

mountainous areas of Colorado and other states in the Rocky 

Mountain region. 

METHODOLOGY AND DATA COMPILATION 

For this preliminary report, I have compiled information on 20 

landslide events (associated with 18 landslides in the state of 

Colorado and one in Wyoming) that occurred during the spring in 
years between 1977 and 1996 . Landslide information was 

gathered from historical newspaper accounts provided by the 

Colorado Historical Society, technical reports, and from my recent 

personal field notes. February thru June issues of local newspapers 

were searched to obtain information on the earliest reported spring 

season landslide occurrences. The reports were found in April, 

May, and June issues of newspapers published in the Colorado 

mountain communities of Aspen, Dillon, Cortez, Steamboat 

Springs, Montrose, and Telluride. A reported landslide event was 

included in this study if it met the following criteria: (1) verifiable 

information on the location and date of occurrence was provided, 

(2) pertinent historical climate data from a nearby weather station, 

including daily temperature maximums and minimums, was 

available, and (3) based on available reports and climatic data, 

snowmelt appeared to be a major factor contributing to the 

occurrence of the landslide event. 

Information obtained in the search on individual landslide events, 

including brief descriptions, dates of occurrence, and sources of 

information, is presented in Table 1. Locations of the landslides are 

shown in Figure 1. During the fall of 1996, I visited the landslide 

sites, plotted their locations on topographic maps, and determined 

elevations. In this preliminary study, no effort was made to further 

determine details of the reported slope failures other than to verify 

the locations, elevations, and times of occurrence. 

In most cases, relatively small movements of a landslide mass, 

often indicated by the development of ground cracks or other 

surface manifestations, precede complete or catastrophic failure. 

For the purpose of this report, the date of landslide occurrence is 

defined as the date of complete or catastrophic failure as indicated 

by large amounts of movement or total disruption of the landslide 

mass. An exception to this are dates I have included for initial, 

spring season movements of a pre-existing landslide in Wyoming 
(landslide events No.1 and 2 in Table 1) that were detected using 

borehole instrumentation (Chleborad, 1980). 

For each of the landslide events listed in Table 1, I compiled 

historical daily precipitation and temperature data recorded at a 

local weather station. Factors that affect the representativeness of 

the data, such as topographic variations, were considered in the 

selection process. In most cases, data from the weather station 

closest to the landslide was selected as most representative. 

Locations, elevations, distances between weather stations and 

respective landslides, and differences in elevation between the 

stations and the landslides are given in Table 2. The climatological 

data was obtained from published reports of the National Oceanic 

and Atmospheric Administration (U.S. Dept. of Commerce, 1977-

1996). Unpublished compilations of the raw climatological data 

and information on the location and elevation of weather observing 

sites were obtained from the Colorado Climate Center, Fort 

Collins, Colorado. 
REPRESENTATIVENESS OF THE CLIMATIC DATA 

The following discussion is based on a recent study of climatic 

data representativeness in western Colorado by Doesken and others 

(1990). The study was conducted for the Bureau of Land 
Management to evaluate to what extent weather stations provide 

representative climatic information for surrounding unmonitored 

areas. In the study, monthly and seasonal climate variability were 

described. It was found that precipitation is much more variable 

than temperature, and that the range of representativeness of local 

weather station data to surrounding areas is much less for 

precipitation than for temperature. Also, Doesken and others 

(1990) showed that there is a good relationship of mean monthly 

maximum temperatures with elevation. It is stated that during the 

summer the relationship is so good that you can typically 

determine the mean monthly maximum temperature to within +/-1 

degree Fahrenheit simply by knowing the elevation. Elevation, 

however, is only a secondary control on minimum temperature, 

especially during the winter months. Relative cold air trapping and 

draining characteristics of a given site become the primary control 

on night time temperatures. A correlation analyses of mean 

growing season (May-September) temperatures vs. elevation 

indicated a decrease of 4.5° F per 1000 ft of elevation (r-squared 

=0.95). Also, correlation patterns developed in the study suggest 

areas in the same valley, regardless of their distance apart, are 

more likely to be well correlated than sites on the opposite sides of 

a mountain barrier. Likewise, stations far apart but with similar 

aspect relative to local terrain, may be better correlated. 

The Doesken and others (1990) study did not address climatic data 

representativeness on time scales shorter than a month. It is stated 

in the report that, in general, variability is increased with shorter 

sampling periods as you go down in time from monthly or 

seasonally to daily or weekly. And, for the shorter sampling 

periods, time series analyses, comparisons and correlations must be 

performed to attempt to determine representativeness. 

For the purpose of estimating historical daily maximum and 

minimum temperatures at the landslide sites, I have assumed that 

the reported relationship between temperature and elevation (-4.5° 

F/1000 ft elevation) is valid for a shorter sampling period. This 

assumption is based on the proximity of the weather stations to the 
respective landslide sites, and the apparent absence of significant, 

intervening terrain factors, such as major mountain divides. 

Because the range of representativeness is much less for 

precipitation than for temperature, I have made no attempt to make 

quantified estimates of historical daily precipitation for the 

landslide sites. 

DATA ANALYSIS and RESULTS 

As a first step, I corrected the raw daily temperature data for 

elevation differences between the weather stations and landslide 

sites using the relationship of Doesken and others (1990). 

Subsequent inspection of the corrected daily temperature data 

revealed that most of the landslide events were preceded by, or 

closely associated with, conspicuous 5- to 10-day intervals of 

rapidly rising temperatures wherein daily maximum temperatures 

typically rose from the 30's or 40's to the 60's or 70's. The mean 

length of the 5- to 10-day intervals was determined to be 6 days. In 

order to examine relationships between dates of landslide 

occurrence and antecedent temperature trends, I computed 6-day 

moving averages of daily maximum and minimum temperatures 

for the parts of each calendar year preceding the occurrence of 

each landslide event. To show antecedent temperature (snowmelt) 

conditions for specific dates, I then plotted the 6-day moving 

averages vs. calendar dates as line graphs with the moving average 

data points coinciding with the last day (calendar date) of the 

respective 6day intervals. Graphs for the periods of time that show 

the association between intervals of rising temperatures and dates 

of landslide events are presented in the appendix (figs. 2-19) 

As shown in Figures. 2-19, the landslide events are preceded by, or 

are coincidental with, conspicuous intervals of rising temperatures 

wherein the 6-day moving averages of daily maximum temperature 

reach into the high 50's or higher. Also note that, in general, the 6-

day moving average of daily minimum temperature is less variable 

than that of the daily maximum temperature. 
In a preliminary effort to identify a threshold temperature that 

might be used to forecast the onset of snowmelt related 

landsliding, I developed graphs showing the association between 

the dates of the landslide events and the first yearly occurrence of 

specific 6-day moving average temperatures. For this purpose, 6-

day moving averages of daily maximum temperatures in the range 

50° to 70° F were used. The following two measures were used in 

the attempt to identify the 6-day moving average of daily 

maximum temperature that would be most useful for forecasting 

purposes: (1) the total number of landslide events that occurred 

within 3 weeks after the first yearly occurrence of the potential 

threshold temperature, and (2) the degree of data clustering near 

the potential threshold temperature; defined as the sum of the 

differences between the landslide event dates and the date of the 

first yearly occurrence of the potential threshold temperature, in 

days. The potential threshold temperature with the highest number 

of landslide events, determined by the first measure, and the lowest 

sum of differences, determined by the second measure, would then 

be selected for forecasting purposes. Based on these criteria, I 

selected a 6-day moving average of 58° F as the proposed 

threshold temperature. However, when the measures were applied 

only minor differences between the 58° F average temperature and 

others in the 55 to 60° F range were apparent, suggesting that more 

sophisticated statistical measures and additional data are needed to 

refine the estimate. Because landslide events No. 1 and 2 were not 

complete landslide failures they were not included in the selection 

process. Landslide events No. 3 and 6 were included by assuming 

a midrange date of occurrence from within the bracketed range. 

Figure 20 shows the dates of the landslide events in relation to the 

first yearly occurrence of a 6-day average greater than or equal to 

58° F. As shown, most of the landslide events occurred within two 

weeks after the first yearly occurrence of the indicated 58° 

threshold. The one event that definitely occurred before the 58° F 

threshold was reached (Landslide event No. 16, fig. 15) was 
preceded by a gradual warming trend that culminated in a 6-day 

moving average of 57° F on the day of the landslide event. 
Because elevation is only a secondary control on minimum 

temperatures and minimum temperatures are less variable than 

maximums, I did not attempt to develop graphs similar to that of 

Figure 20 for the daily minimums. It seems reasonable to expect a 

close association between the onset of snowmelt related landslides 

and the first yearly occurrence of sustained daily minimum 

temperatures above freezing (32° F). However, visual examination 

of the plots (figs. 2-19) indicate that, although there appears to be 

an association, only about half of the 20 landslide events preceded 

the first yearly occurrence of a 6-day moving average greater than 

or equal to 32° F; therefore, it would not be as useful for 

forecasting the onset of spring season landslides as the 6-day daily 

maximum average of 58° F. 

As previously stated, I have assumed that the reported relationship 

between temperature and elevation (-4.5° F/1000 ft of elevation 

increase) is valid for the 6-day sampling periods. A study of 

temperature representativeness for the relatively short distances 

considered in this study is beyond the scope of this report. 

However, the few comparisons I have made of daily temperature 

data recorded at weather stations separated by similar distances 

suggests a good correlation. An example is the 6-day moving 

averages of daily maximum temperature from the Sheridan AP 

weather station (fig. 2) and that for the same March 6 to April 30, 

1977 period from a weather station located 7 mi to the northeast 

(Sheridan Field Station). Comparison of the data (corrected for an 

elevation difference of 240 ft) is shown in Figure 21. 
DISCUSSION AND CONCLUSIONS 

The results of this preliminary study suggest that temperature data 

recorded at weather stations throughout the Rocky Mountain 

region is potentially a valuable source of information for 

forecasting the onset of spring season landslides. Beginning in 

March of each year, moving averages of real-time daily 

temperatures obtained from local weather stations could be used to 

pinpoint the first occurrences of the threshold temperature in the 

respective areas of interest. Forecasts could then be issued to the 

media and appropriate government agencies warning of the 

increased potential for landsliding. In addition to insuring public 

awareness, the forecasts could be used for such things as planning 

and scheduling highway maintenance, timing the deployment of 

field instrumentation, and monitoring potentially hazardous 

landslide masses. 

Although the combination of deep snowpack and warming trends 

sufficient to cause significant snowmelt usually occur in the spring 

of each year in the central Rocky Mountains, it can occasionally 
occur at other times of the year as well. It follows that the first 

yearly occurrence of the threshold temperature may, on occasion, 

arrive before the spring season. Also, areas outside of the area of 

this study that have significantly different regional climates have 

experienced widespread landsliding involving snowmelt with rainon-snow storms during the winter months (e.g., Day and Megahan, 

1976). Temperatures and temperature trends associated with those 

events may differ significantly from those of this study. 

This study is based on a limited number of spring season landslide 

events and only minimal amounts of information on the various 

geologic, hydrologic, and climatic factors that may have 

contributed to their occurrence. Additional work is needed to 

expand the landslide database and further evaluate the 

representativeness of the temperature data. Such work would likely 

result in refinement of the threshold value and an improved 

forecasting capability. 

REFERENCES

Aspen Daily News, 1993, Reconnected again; the Pass opens 

early: Aspen, Colorado, May 28, p. 1 and 6. 

Aspen Times, 1983, Redstone mud scare causes evacuation of 

valley residents: Aspen, Colorado, June 2, p. 10. 

Chleborad, Alan F., 1980, Investigation of a natural slope failure 

in weathered Tertiary deposits, western Powder River Basin, 

Wyoming: U.S. Geological Survey Open-File Report 80-673, 66 p. 

Day, N.F., and Megahan, W.F., 1976, Landslide occurrence on 

mountainous terrain in north central Idaho: A progress report, 

1974-75: Proceedings of the 14th Annual Symposium of 

Engineering Geologists and Soils Engineeers, Boise State 

University, April 7,8, and 9th, p. 85-104. 
Doesken, Nolan J., McKee, Thomas B., and Kleist, John, 1990, 

Climatic data representativeness in western Colorado: Colorado 

State University Climatology Report No. 90-1, 43 p. 

Montezuma Valley Journal, 1979, Slides on Mesa Verde: Cortez, 

Colorado, April 20, p. 1. 

Montezuma Valley Journal, 1979, Mesa Verde remains closed: 

Cortez, Colorado, May 2, p. 1. 

Schuster, Robert L., 1986, Amtrak wreck caused by landslide 

near Granby, Colorado: Ground Failure, National Research 

Council Committee on Ground Failures, No. 3, Spring 1986. 

Steamboat Pilot, 1982, Mud slides damage ski jumps: Steamboat 

Springs, Colorado, May 13, 

p. 1. 

Steamboat Pilot, 1982, See Me, see mudslide: Steamboat Springs, 

Colorado, May 27, p. 1. 

Steamboat Pilot, 1984, Rising waters flood Route County: 

Steamboat Springs, Colorado, 

May 17, p. 1. 

Steamboat Pilot, 1993: Mud slides down runs at ski area: 

Steamboat Springs, Colorado, 

May 27, p. 1. 

Stover, B.K., Cannon, S.H., and Junge, Rahe W., 1987, The April 

30, 1987 Telluride Airport landslides and resultant debris flows: 

Colorado Geological Survey Department of Natural Resources 

Open-File Report 87-2, 14 p. 

Summit County Journal, 1984, Mudslide blocks Blue River: 

Dillon, Colorado, June 14, p. 3. 

Telluride Times, 1984, Woman dies in mud slide; melting snow 

wrecks county roads: Telluride, Colorado, May 17, p.1. 

Umstot, David, 1989, Field studies and modeling analysis of the 

Roan Creek landslide, Garfield County, Colorado: Colorado 

Geological Survey Department of Natural Resources Open File 

Report 89-1, 67 p. 

U.S. Department of Commerce, 1977, Wyoming climatological 

data: Daily temperature data, 
v. 86, No.s 1-4. 

U.S. Department of Commerce, 1978, Wyoming climatological 

data: Daily temperature data, 

v. 87, No.s 1-4. 

U.S. Department of Commerce, 1979, Colorado Climatological 

Data: Daily temperature data, 

v. 84, No.s 1-5. 

U.S. Department of Commerce, 1982, Colorado Climatological 

Data: Daily temperature data, 

v. 87, No.s 1-5. 

U.S. Department of Commerce, 1984, Colorado Climatological 

Data: Daily temperature data, 

v. 89, No.s 1-5. 

U.S. Department of Commerce, 1985, Colorado Climatological 

Data: Daily temperature data, 

v. 90, No.s 1-4. 

U.S. Department of Commerce, 1987, Colorado Climatological 

Data: Daily temperature data, 

v. 92, No.s 1-5. 

U.S. Department of Commerce, 1993, Colorado Climatological 

Data: Daily temperature data, 

v. 98, No.s 1-5. 

U.S. Department of Commerce, 1996, Colorado Climatological 

Data: Daily temperature data, 

v. 101, No.s 1-5 

APPENDIX 

(Figures 1-21) 

Figures for U.S. Geological Survey Open-File Report 97-27
* Figure 1.--Index map of Colorado and Wyoming showing the 

locations of landslides included in the study. Numbers shown are 

those of landslide events listed in Table 1. 

* Figure 2.--Graph showing the association of landslide event 

No. 1 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 3.--Graph showing the association of landslide event 

No. 2 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 4.--Graph showing the association of landslide events 

No. 3, 4, and 5 with rising temperatures and the first yearly 

occurrence of a 6-day moving average of daily maximum 

temperature greater than or equal to 58° F. 

* Figure 5.--Graph showing the association of landslide event 

No. 6 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 6.--Graph showing the association of landslide event 

No. 7 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 7.--Graph showing the association of landslide event 

No. 8 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 8.--Graph showing the association of landslide event 

No. 9 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 9.--Graph showing the association of landslide event 

No. 10 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 
* Figure 10.--Graph showing the association of landslide event 

No. 11 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 11.--Graph showing the association of landslide event 

No. 12 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 12.--Graph showing the association of landslide event 

No. 13 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 13.--Graph showing the association of landslide event 

No. 14 with an antecedent interval of rising temperatures and the 

first yearly occurrence of a 6-day moving average of daily 

maximum temperature greater than or equal to 58° F. 

* Figure 14.--Graph showing the association of landslide event 

No. 15 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 15.--Graph showing the association of landslide event 

No. 16 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 16.--Graph showing the association of landslide event 

No. 17 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 17.--Graph showing the association of landslide event 

No. 18 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 18.--Graph showing the association of landslide event 

No. 19 with rising temperatures and the first yearly occurrence of a 
6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 19.--Graph showing the association of landslide event 

No. 20 with rising temperatures and the first yearly occurrence of a 

6-day moving average of daily maximum temperature greater than 

or equal to 58° F. 

* Figure 20.--Plot showing dates of landslide events in relation 

to the first yearly occurrence of a 6-day moving average of daily 

maximum temperature greater than or equal to 58° F. Plotted 

numbers are landslide events identified in Table 1 and Figures 2-

19. Note that a high percentage of the landslide events occurred 

within 18 days of the first yearly occurrence of the proposed 58° F 

threshold. 

* Figure 21.--Comparison of 6-day moving averages of daily 

maximum temperatures recorded at Sheridan AP and Sheridan 

Field Station weather stations during the period March 6 to April 

30, 1977. 

Alan F. Chleborad

* U.S. Geological Survey 

* Geologic Hazards team 

* Landslide Hazards Group 

* email: chleb@gldvxa.cr.usgs.gov

* P.O. Box 25046, MS 966 

* Lakewood, CO 80225