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Glaciers of
the
Sierra Nevada
This
page highlights my research
on glacier change in the Sierra Nevada. My
complete masters thesis entitled "Quantifying Twentieth Century Glacier Change in the Sierra Nevada,
California" can be found here (pdf).
Numerous
small alpine glaciers occupy the high elevation regions of the central and
southern Sierra Nevada, California. These glaciers change size in
response to variations in climate and are therefore important indicators of
climate change. While knowledge of glacier shrinkage in the Sierra Nevada is common, there is little quantitative
information on the magnitude or rate of reduction. The purpose of my thesis was to:
- Define the number and spatial extent of the Sierra Nevada glacier
population
- Quantify the magnitude and rate of change in glacier extent for a small
subset of glacier
- Compare the rates of change against climate variations.
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Background
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The Sierra
Nevada
extend over 400 miles forming a mountainous spine along eastern
California. The beautiful alpine landscapes of the High Sierra owe much
of their existence to the work of glaciers that have sculpted the
bedrock through time. Within the southern and central regions of the
Sierra Nevada, small glaciers are still at work, slowly eroding the
high peaks and ridges, and depositing rock material below. The Sierra
Nevada glacier population consists of approximately 498 ice features,
including perennial ice patches and mountain glaciers (Raub et al.,
1980). These features are small in size ranging from small ice patches
with areas of less than 0.1 km2, to Palisade Glacier, the largest in
the Sierra Nevada with an area of 1.58 km2 (Raub et al. 1980). These
glaciers are remnants from a cool period in the climate referred to as
the Little Ice Age (Matthes, 1940; Porter, 1981). Climatic cooling
began around 1350 AD, during which time glaciers began to form and
advance. This cool period persisted roughly through 1850 AD, at which
time Sierra Nevada glaciers are thought to have reached their maximum
extent for the Little Ice Age. Since that time, mountain glaciers
throughout the world have showed signs of overall recession during the
past century. |
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The central and
southern Sierra Nevada with glaciers highlighted in red to show modern
extent
(MODIS image) click for
larger view |
Glaciers
and
Climate
Alpine glaciers are recognized as indicators of climate change because
they change in mass and geometry in response to climatic changes
(Meier, 1965). The link between changes in climate and glacier geometry
is complex and indirect. The meteorological environment determines
accumulation and ablation at a glacier, on which a glacier’s mass is
dependent. A change in mass produces a dynamic response within a
glacier that causes changes in glacier geometry. Observations in
glacier geometry through time can therefore provide an indication of
long-term climatic variations and environmental change in alpine areas.
Sierra
Nevada climate
is
complicated by local topographic variables that can exert a degree of
control over regional
climate.
These variables include elevation, aspect, and slope. Alpine landforms
such cirque headwalls and ridges can modify local climate by
reducing incoming solar radiation through shading, reducing local
temperatures,
and altering or intensifying wind patterns. Glaciers in the Sierra
Nevada typically exist in north and
northeast facing cirques as these location receive less
incoming solar radiation.
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The view from Mount
Darwin
looking south toward Evolution Valley. Snow and ice remain in
north and northeast cirques that are protected from incoming solar
radiation.
(H. Basagic 2003) |
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Preliminary
Results
Comparisons of
the repeat photography reveal that all ten glaciers surveyed in 2003
and 2004 have experienced a reduction in ice volume and surface extent
over the past century. Repeat photography is a valuable tool in
determining change through time, especially when combined with aerial
photos and field measurements. A case example at Lyell Glacier
indicates the surface area of the west lobe has been reduced by 35%
since 1883, and the smaller east lobe has been reduced by 70%. These
results support the idea that topographic controls strongly influence individual
glacier response to regional and global climate change.
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| References
Matthes,
F.E., 1940. Commitee on glaciers, 1939-1940. Transaction, American
Geophysical
Union: 396-406.
Meier,
M.F.,
1965. Glaciers and climate. In: H.a.F.D. Wright (Editor), The
quaternary of the
United States. Princeton University Press, Princeton, N.J.
Porter,
S.C.,
1981. Glaciological evidence of Holocene climatic change. In: T.M.L.
Wigley,
Ingram, M.J. and Fermer, C. (Editor), Climate and History. Cambridge
University
Press, Cambridge.
Raub,
W.B., Post,
A., Brown, C.S. and Meier, M.F., 1980. Perennial ice masses of the
Sierra
Nevada, California, World glacier inventory. IASH-AISH Publication 126:
33-34
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More information:
POSTER: Basagic H., Fountain A., Documenting Twentieth Century Glacier
Change with Repeat Photography in the Sierra Nevada, California (pdf) |
Questions or comments? please
contact me: basagic"AT"pdx.edu
Created: 06/04/04; modified: 05/20/08
Link to Hassan's Homepage
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