Twentieth Century Glacier Change in the
Sierra Nevada, California


HASSAN BASAGIC

Geology Department
Portland State University 













Darwin Glacier, Kings Canyon National Park. This image illustrates glacier change in the Sierra Nevada. The image toggles between a photograph taken on August 14, 1908 by G.K. Gilbert and a photograph taken on August 2, 2003 by Hassan Basagic.
     
DarwinGlacier
        



       

Glaciers of the Sierra Nevada 

This page highlights my research on glacier change in the Sierra Nevada. A publication and my thesis entitled "Quantifying Twentieth Century Glacier Change in the Sierra Nevada, California" are available: Thesis (2008) Publication (2011)

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 was 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, and compare the rates of change against climate variations.

Where do glaciers occur in the Sierra Nevada?


Glaciers are found high in the Sierra Nevada, generally above 10,000 feet in elevation, on the north sides of steep mountains from Yosemite National Park in the north to Sequoia National Park in the south. Sierra Nevada glaciers are typically located in mountain cirques, which are small bowl-like depressions on the sides of mountains which were created by previous glaciers.

The number of glaciers in the Sierra Nevada depends on the definition. The definition of a glacier is a body of perennial ice or snow that moves. Movement of ice can be observed as cracks in the ice known as crevasses. Because Sierra Nevada glaciers are small and remote previous glacier inventories have placed the number between 50 and 500 glaciers. My survey, based on USGS topographic maps (1:24,000 scale), counted over 1700 glaciers and snow and ice patches. Many snow and ice bodies which do meet the definition of a glacier. I estimated the number of "true glaciers" at 118 glaciers in the Sierra Nevada based on theoretical considerations.

extent
The central and southern Sierra Nevada with glaciers highlighted in red to show modern extent
(MODIS image)
How have glaciers changed over the past century?

Sierra Nevada glaciers have become smaller over the past century. This is evident from early photographs which reveal these glaciers occupying their moraines around 1900. Today, the glaciers have receded up the mountains and appear deflated. I quantified the surface area change by selecting fourteen glaciers throughout the Sierra Nevada and measured the change using historical photographs, geologic evidence, and field mapping. I determined the glaciers lost and average of 55 percent of their surface area by 2004. The decrease in surface area of individual glaciers ranged between 31 and 78 percent.

I selected a subset of seven glaciers to determine the rate of change over the past century. The results indicated that glaciers rapid retreated occurred over the first half of the twentieth century beginning in the 1920s in response to warm/dry conditions and continued through the mid-1970s. Recession ceased during the early 1980s, when some glaciers advanced. Since the 1980s each of the seven study glaciers resumed retreat.

fig23

Glacier Repeat Photography 

Comparisons of the repeat photographs 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.
Please contact me if you are interested in using these photographs.

Darwin Glacier Darwin Glacier 1908 Darwin Glacier 2004
August 14, 1908    G.K. Gilbert August 14, 2004     H. Basagic
Lyell Glacier Lyell Glacier 1903 Lyell Glacier 2003
August 7, 1903   G.K. Gilbert August 14, 2003    H. Basagic
Dana Glacier Dana Glacier 1883 Dana Glacier 2004
August, 1883   I.C. Russell    September 8, 2004   H. Basagic
Sierra Nevada Glacier Photographs

Here are some examples of glaciers in the Sierra Nevada from the Glaciers of the American West Photo Archive:


       Maclure Glacier
       Palisade Glacier
       Darwin Glacier
       Dana Glacier

If you are interested in more glacier photos visit our glacier photo archive.

evolution valley

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)
Please refer to my thesis for a complete list of references.

Back to top of page

Glacier Links
Glaciers of the American West - Portland State University's glacier database. Includes interactive maps, historical photos, and reports.
The Glacier RePhoto Project - Repeat Photography in the American West
Portland State University Glacier Research Home
Inventory of Glaciers in the Sierra Nevada, California   Raub, W. B., Brown, C. S. and Post, A. 2006 US Geological Survey Open-File Report 2006-1239.
Links of Interest
Altered State: Climate Change in California - California Academy of Sciences Climate Change exhibit in Golden Gate Park, San Francisco, CA 
Final Flight - Peter Steckle's book on the 1942 plane crash at Mendel Glacier
Glacier Survey: Embrodery and heat transfer work by artist Bonney Petersen, featuring changes at Lyell Glacier, Yosemite.
Additional 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"gmail.com
Created: 06/04/04; modified 07/19/14
Link to Hassan's homepage