April 22, 2012

Romanzof Glacier Retreat. Brooks Range, Alaska

Posted by Mauri Pelto

In the Romanzof Mts. Brooks Range, Alaska McCall Glacier and Okpilak Glacier have been the main focus of research. These glaciers are much smaller than glaciers in southern Alaska, as the region has much more limited amounts of snowfall. The University of Alaska-Fairbanks have focused on McCall Glacier average rate of thinning increased between 1956–93 and 1993–2002, averaging 0.4 m/year for the entire period. The primary region of thinning was the lower third of the glacier below 1700 meters (Nolan et al, 2005). The glacier had retreated 800 meters from the Little Ice Age moraine by 2000 (Nolan et al, 2005). The Equilibrium Line Altitude has risen from 2050 in the 1970’s to 2250 m recently, leading to continued and more rapid losses in ice volume (Delcourt et al, 2009). Okpilak Glacier had retreated 2 km from its Little Ice Age moraine by 2006.

In this post we examine the Romanzof Glacier. The first image indicates the various tributaries feeding into the main valley glacier, burgundy arrows, the reach of well developed stream channels, green arrows. The red line is the map terminus and the yellow line the 2009 terminus. The map is the USGS topographic map from 1956 aerial photographs This glacier has retreated 1300 meters from its 1956 mapped position and 1900 meters from its Little Ice Age moraine, blue line in first image below. The glacier remains 5 km long, having lost 25% of its length in the last 50 years. The rate of ice loss like on McCall Glacier has accelerated. A view of the middle of the ablation zone indicates some well developed stream channels, green arrows. Channels like this take multiple years to form and indicate limited glacier velocity. Closer to the terminus the stream channels are even larger, green arrows. The streams have matured developing meanders, this tends to occur only where the surface is stagnant. This indicates the lower 1200-1500 meters of the glacier is stagnant and melting away quickly. In addition there are some ridges of ice cored moraine indicating that the bare ice is melting faster than the ice under the moraine debris, violet arrows. The bluish arrows indicate where the subglacial streams have emerged from beneath the ice indicating the terminus.