Sourdough Glacier descends the north side of Klondike Peak in the Wind River Range of Wyoming. Thompson et al (2011) identified the loss in area of Wind River Glaciers from 1966 to 2006. The total surface area of the 44 glaciers was estimated to be 45.9 km2 in 1966 and 28:6 km2 in 2006, a decrease of 42%. The retreat has varied from substantial on Minor and Grasshopper Glacier to limited on Upper Fremont Glacier. For Sourdough Glacier the 1966 USGS map of the area based indicates the glacier ending in a small lake, orange line in images. We use 1994, 2006 and 2009 images in Google Earth to examine the glacier changes. By 1994 (green line) the glacier had retreated 160 meters and the lake nearly doubled in size. By 2006 (magenta line) retreat from 1966 was 280 meters with a more pronounced calving face developing. In 2009 the calving face remains and the glacier had retreated another 20 meters overall, 40 meters in the glacier center. The increased height of the calving face suggests the lake is deeper than at the 1994 terminus position and that the lake will continue to expand with further retreat. The calving front and slope of the glacier is similar to Lyman Glacier. The retreat from 1966-2006 is a 20% reduction in overall glacier length. If a glacier lacks a persistent accumulation zone it will not survive (Pelto, 2010). The key indicator of a glacier without a consistent accumulation zone if retreat of the upper margin of the glacier and emergence of rock outcrops on the upper glacier. There are some limited changes of this nature on Sourdough Glacier, but most of the change has been at the terminus. The forecast for survival of Sourdough Glacier is not as clear cut as on Minor and Grasshopper Glacier. The crevasses indicate the glacier is still actively moving.
The Wind River Range is host to 40 glaciers that all have retreated significantly over the last 25 years and 45 years. Of the 15 glaciers observed in detail, nine will not survive current climate (Pelto, 2008). The Lower Fremont is one of the glaciers that will not survive. A comparison of its extent from 1966 USGS map, 1994 USGS aerial photography and 2006 satellite image in Google Earth indicate the retreat. The 1966 glacier boundary is outlined in orange. . The glacier has lost 23 % of its area and the terminus has 130 retreated meters. A new lake has formed since 1994 at the terminus, and new outcrops of rock have emerged, as noted in the combined 1994-2006 image below.The key changes that indicate the glacier is not going to survive are the outcrops of rock that have emerged in the upper portion of this glacier, blue arrows. The new lake is indicated by the red arrow. The green arrows indicate the numerous firn layers exposed at the surface. Both the exposure of firn layers and the emergence of bedrock and rock through the glacier indicates the lack of a consistent and persistent accumulation zone. This indicates the glacier will not survive ((Pelto, 2010 and Pelto, 2011).