November 7, 2009
The glaciers of Denali National Park are shrinking. The National Park Service has been chronicling the retreat with repeat photographs of glaciers from locations where historic photographs exist. The program has been a cooperation between glaciologist Guy Adema and photographer Ron Karpillo. One example is East Taklanika Glacier. This glacier drains north from the east ridge of Mount Scott. The glacier is currently 5.1 km long, the lower 2.2 km of the glacier is nearly completely debris covered. That ice is beneath the debris is clear from the lack of a the glacier melt fed river in the valley bottom and the color of the sediments which is darker, largely because the debris is wet from the ice melt underneath. The glacier in the center of the Google Earth satellite view below is East Taklanika Glacier. The glacier has retreated 1100 m between 1916 and 2004 in the phtographs of Ron Karpillo and Stephen Capps. There is a lateral moraine in the foreground of the 2004 Ron Karpillo image. This marks the former surface elevation of the glacier during the Little Ice Age. Since that time the lower section of the glacier has lost over 100 m of ice thickness. The retreat is ongoing. Medial moraines are bands of debris on the surface of a glacier that separate tributaries of a glacier. The moraines represent material eroded from the edge of the tributaries before they join. This material does not appear at the surface until you reach the ablation zone where melting dominates. In the accumulation zone such debris bands would be buried. On East Taklanika Glacier the debris bands extend to within 1 kilometer of the head of the glacier. For a glacier to be in equilibrium a glacier needs to have at least 50 % of its area in the accumulation zone at the end of the summer. Based on the satellite image hear showing 10% of its area in the accumulation zone and the extent of the medial moraine indicating no more than 25% of the glacier area above the moraine. This glacier needs to lose the lower 2-3 kilometers to be in equilibrium. This may not be enough. A glance at the glaciers around East Taklanika, indicate the same story, very little retained snowpack. Some of these glaciers have an accumulation area ratio (% of glacier snow covered at the end of the summer), of zero. This is like having no income, and plenty of expenditures and the result for your bank account, net loss and without some change eventual bankruptcy. The story of retreat is the same though the snowpack extent greater on the Juneau Icefield. The retreat of East Taklanika is slowed considerably by the debris cover which protects the ice underneath from melting as fast. This glacier is a long way from completing its retreat to adjust to current climate.