June 13, 2010

Grasshopper Glacier Wyoming disappearing

Posted by Mauri Pelto

Grasshopper Glacier in the Wind River Range of Wyoming has a southern terminus calving into a lake , sometimes referred to as Klondike Glacier, and a northern terminus. The southern terminus is calving and retreating expanding the unnamed lake it terminates in. The southern glacier has retreated 350 m since 1966. This lakes drains north under the glacier and down the valley under the Grasshopper Glacier. This is quite unusual to have a stream draining under the glacier from a lake at a terminus of the glacier. The lake can drain to the east if it rises to the 12,000 foot threshold. This was the case in 1994. The terminus area is not being fed by the upper accumulation zone to the northwest any longer. The terminus is stagnant and will continue to melt away. The lake has existed since at least 1950. In 2003 it drained substantially and quickly below the glacier causing a downstream flood. An ice dam break released a glacier flood is a jokulhaup. The lake was reported by the USGS to have drained 90%. In the 2006 image it has largely refilled, but notenough to drain to the east again. It is likely given the stagnant nature of the glacier, that the drainage conduit will not be fully closed, and the lake can drain through the channel on more of an ongoing basis. The northern terminus has retreated 730 m the most extensive retreat in the Wind River Range. The main accumulation area on the west side of the glacier has become segmented by large bare rock areas as noted by comparing the 1966 map and 2006 image. The 1966 boundary indicated in orange noted area circled in burgundy in the second image below. The combined retreat of the two terminus is over one kilometer this is 40 % of its 1966 length of 2.4 km. The significant thinning and marginal retreat at the head of the glacier is symptomatic of a glacier that will disappear with current climate. The glacier seldom has significant snowcover at the end of the melt season is with the current climate will melt away. In 2009 the glacier did have significant snowcover at the end of the melt season for only the third time in the last 10 years.