Glaciers of the Sierra Nevada

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.

The central and southern Sierra Nevada with glaciers highlighted in red to show modern extent (MODIS image) click for larger view

Glaciers and Climate

Research

    The purpose of my research is to quantify the rate and magnitude of change glacier extent over the past century in Sierra Nevada. A reduction in Sierra Nevada glaciers can be assessed by comparing photography of glaciers taken over the past century (see above and below). While knowledge of glacier shrinkage is common, there is little quantitative information on the magnitude or the rate of this reduction. I specifically propose to:
          1) define the glacier population and extent in the Sierra Nevada using USGS topographic maps (1:24,000 scale);
          2) quantify the rate and magnitude of change in glacier extent using six index glaciers;
          3) compare the rates of change against climate records, and
          4) examine the climatic and topographic controls on the presence and absence of glaciers and perennial ice bodies throughout the Sierra Nevada.
I am compiling previous extents of several glaciers using terrestrial and aerial photographs and mapping these changes in a Geographic Information System (GIS). Repeat photography will serve as a visual comparison and aid mapping efforts. The start date roughly follows the maximum of the Little Ice Age in the Sierra Nevada. 

    

Sierra Nevada Glacier Photographs Here are some examples of glaciers in the Sierra Nevada taken in 2003 by Hassan Basagic:        Maclure Glacier        Palisade Glacier        Darwin and Mendel Glaciers        Dana Glacier
	A comparison of Lyell Glacier, Yosemite National Park in 1903 (top) taken by G.K. Gilbert, and 2003 (bottom)  taken by Hassan Basagic.

		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.