The Changing Glaciers of Mt. Hood, Oregon and Mt. Rainier, Washington:
Implications for Periglacial Debris Flows
Jonathan Ellinger and Anne W. Nolin
Department of Geosciences, Oregon State University
INTRODUCTION
Scientific Rationale
Mountain glaciers are receding worldwide with numerous
consequences including changing hydrology and
geomorphology.
Finding a way to accurately measure the changes in
glacier dimensions over time may provide further insights
into understanding where and how damaging periglacial
debris flows are initiated.
Project Objectives
fsdf
1. Map changes in glacier ice area on Mt. Hood, OR
and Mt. Rainier, WA
2. Examine these changes in glacier area in relation to
initiation sites of recent debris flows
Figure 1. Locations of the two study areas.
BACKGROUND AND PREVIOUS WORK
Previous studies have used Landsat Thematic Mapper (TM) data to map glacier
areas (Taschner and Ranzi, 2002; Paul et al, 2007; Racoviteanu et al., 2008). The ratio
between TM band 4 (0.75-0.90µm) to TM band 5 (1.55-1.75µm) was found to enhance
the reflective differences of the glaciers allowing clearer glacier outlines to be discerned
(Hall, et al, 1987). Bands 1-5 of the TM sensor are in the visible and near-infrared parts
of the electromagnetic spectrum. Band 4 shows the greatest variability in spectral
response to glacierized areas while band 5 is very good at distinguishing between clouds
and snow (Hall et al, 1987).
With Landsat imagery now available free to the public, the possibility of studying glacial
change can be realized. This is the first time Landsat data will be used to monitor
changes in glacier area on Mt. Rainier and Mt. Hood and will provide a useful tool for
monitoring climate impacts on glaciers in the future.
.
PERIGLACIAL DEBRIS FLOWS
Debris flows are defined as “a rapid, gravity-induced mass movement consisting of
sediment mixed water and air” (Varnes, 1978). Periglacial debris flows originate near the
terminus of a glacier where large quantities of loose rock are left behind as glaciers
recede up the mountain. In November 2006, numerous debris flows were triggered as the
result of a large storm that dropped record amounts of rainfall at high elevation sites. The
debris flows appear to have initiated in sediments exposed by recent retreat of glaciers.
METHODOLOGY
Cloud-free Landsat scenes from the August-September period of 1984—2009 were used
to compute debris-free glacier area for 11 glaciers on Mt. Hood and 27 glaciers on Mt. Rainier.
Debris free glacier area was computed using the normalized difference (ND) of Band 4 and
Band 5 (Figure 2).
An orthorectified high resolution aerial photograph (NAIP 2005) of Mt. Hood was used
to delineate glacier area in order to establish the threshold for glacier v.s non-glacier. A value of
0.05 gave the best fit to the debris-free ice area in the 2005 NAIP photo. Previously mapped
glacier outlines were provided by the research group of Dr. Andrew Fountain, Portland State
University.
SNOTEL (SNOpack Telemetry) data from sites on Mt. Hood and Mt. Rainier were used
to identify years with the least late season snow remaining on the mountains and were
compared with corresponding Landsat scenes to eliminate years where seasonal snow obscured
the extent of glacier ice.
Figure 5. Landsat-derived map of changes in debris-free glacier ice for Mt. Rainier. 2006
debris flow initiation sites are shown as yellow dots.
Figure 2. Landsat TM Band 4 (left), Band 5 (center), and the normalized difference ratio (right)
To convert projected area (A) to slope-corrected area (A’) of each glacier, a LiDARderived digital elevation model (DEM) was used to compute the average slope of each glacier
pixel. For each glacier pixel, the slope-corrected area was computed as: A’ = A/cos(slope).
RESULTS
Figures 3 and 4 show the change in area for each glacier on Mt. Hood and Mt. Rainier.
Figure 5 maps the decreased extent of glacier area on Mt. Rainier in relation to debris flow
initiation sites. The SNOTEL data indicate that years 1987, 1992, and 2005 had the earliest
date snow disappearance and the years 2000 and 2005 had the total lowest snow water
equivalent. Temperature data from the SNOTEL stations show that years 1992 and 2005 also
had the highest average temperature.
The total slope-corrected area of glacier retreat on Mt. Hood decrease from 14.7 km2 to
12.6 km2, a total change of 13.9%. For Mt. Rainier, the slope-corrected area decreased
from 78.7 km2 to 67.7 km2, a 14.0% decrease.
DISCUSSION & CONCLUSION
The area of nearly every glacier on Mt. Hood and Mt. Rainier decreased over the period
from 1987-2005. The presence of seasonal snow limits our ability to accurately map glacier area
using satellite imagery. This should serve as a caution to researchers who use only single years of
image data to map glacier extent. In situ data such as SNOTEL measurements of snow water
equivalent and air temperature are useful tools for helping to identify optimal years for glacier
mapping. Glacier outlines from ground-based or high resolution aerial surveys are also needed to
establish appropriate thresholds for classification of glacier ice and to serve as references for
determining change.
Debris flow initiation sites from the November 2006 events are all located within regions
of recent glacier retreat, suggesting a relationship between glacier retreat and debris flow
initiation. What is still needed is a means of mapping debris-covered glacier ice from satellite.
This study shows that freely available Landsat imagery can effectively be used to monitor glacial
changes in relatively small glaciers such as those on Mt. Hood and Mt. Rainier.
References
Hall et al. 1987. Characterization of Snow and Ice Reflectance Zones on Glaciers using Landsat Thematic Mapper
Data. Annals of Glaciology 9:104-108
Paul et al. 2007. Recent Glacier Changes in the Alps Observed by Satellite: Consequences for Future Monitoring
Strategies. Global and Planetary Change 56(1-2):111-122.
Racoviteanu et al. 2008. Optical Remote Sensing of Glacier Characteristics: A Review with Focus on the
Himalaya. Sensors 8:3355-3383.
Taschner and Razi. 2002. Comparing the Opportunities of Landsat TM+ and ASTER Data For Monitoring a
Debris Covered Glacier in the Italian Alps with the GLIMS Project. International Geoscience and Remote Sensing
Symposium 2: 1044-1046.
Varnes, D.J. 1978. Slope Movement Types and Processes. In: Special Report 176: Landslides: Analysis and
Control. Transportation and Road Research Board, National Academy of Science, Washington D.C., 11-33.
Acknowledgements
Fig 3. Mt. Hood % of Debris-Free Ice Loss 1987-2005
Fig 4. Mt. Rainier % of Debris-Free Ice Loss 1987-2005
Glacier outline data were graciously provided by Dr. Andrew Fountain, Portland State University
Landsat data were provided by the EROS Data Center, USGS.
LiDAR data provided by Watershed Sciences, Inc.
Funding for this project was provided by the National Science Foundation, grant (Award 0844017, Geomorphology
and Land Use Dynamics) “Climatic and Geomorphic Triggering Mechanisms of Cascadian Periglacial Debris Flows”