June 10, 2013

Neve Glacier Retreat, North Cascades, Washington

Posted by Mauri Pelto

I have had the opportunity to visit the Neve Glacier on eight occasions, it is not easy to get to. In the North Cascades it is one of a handful of glaciers with a large higher elevation accumulation zone, that is not on a volcano. The glacier feeds Diablo Lake, part of the Skagit River hydropower system. The terminus of the glacier in 1975 was in basin that receives considerable avalanche deposition slowing the retreat. In this post we focus on the thinning of the glacier leading to expansion of bedrock exposures at four locations above the former terminus, that by 2011 had led to this low lying basin being dynamically cutoff from the upper glacier. In each image the red letters A-D are located in the same spot, and the purple arrow on the Google Earth images indicates the terminus position. The first image is an aerial view of the glacier from Austin Post, USGS from 1975: at point A there is a quite small exposure of bedrock, at Point B and C there is a good connection of feeder glaciers from the higher slopes to the main valley glacier. At Point D there is continuous glacier cover. This was the case during my first two visits to the glacier in 1985 and 1988, second image. The third image is from 1990 and reflects limted change from 1975 as well, the blue arrows indicate glacier flow.

. By 1996 notable thinning of the glacier was apparent adjacent to Point A, in 2001 and 2002 the thin nature of the ice around the bedrock at Point A is evident. . The accumulation zone of the glacier around Point B and D in 2001 indicates no bedrock exposure at D and a connection of the upper glacier at Point B; however at Point D in 2009 the large new bedrock areas that have resulted from thinning has occurred. A comparison of the Google Earth imagery from 1990, 2006 and 2009 indicate the expanding bedrock at each Point. A closeup of Point A from 2009 has the bedrock delineated with red dots indicating that the left arm of the glacier that formerly encircled Point A, now ends above Point A and that the right hand arm is only 35 m wide and despite the steep slope has no crevassing and is stagnant. At Point B the upper glacier no longer reaches the main trunk. At Point C the connection to the main glacier has decreased by 50% in its width from 140 m to 70 m, and at Point D several large bedrock areas have emerged. In 2013 or 2014 the upper glacier will likely separate from the former terminus region below the Point A bedrock region. The thinning of this glacier is typical of North Cascade glaciers (Pelto, 2007), though the retreat has been unusually small (Pelto, 2010).