From a Glaciers Perspective

Sawyer Glacier is an Alaskan glacier that many people have observed the retreat of. It is one of three glaciers that calves into Tracy Fjord, that is often visited by cruise ships. The 2.3 km retreat over the last 50 years has made approach to the actual terminus difficult for larger cruise ships. The terminus of the glacier was almost to the main arm of the fjord in 1961, USGS map. The 2003 Google Earth images indicates a 2.3 km retreat. The green line down fjord marks the 1961 terminus, the upfjord line is at the 1100 foot contour of the USGS map and is parallel with the current terminus location. The snowline of the glacier was noted to be at 1125 meters by Pelto (1987), using Landsat images. At the time usable images were rare. Today images are acquired daily by MODIS and if the weather is clear, which is not common, the snow line is evident. Recent satellite images from 2006 and 2009 indicate the snow line still in the 1100 to 1200 meter elevation region, however, the 300+ meter thinning at the terminus has led to thinning upglacier and the location of the 1100 meter contour has shifted 1-1.5 kilometers upglacier. The snowline is evident in the 2003 Google Earth image. The snowline is also evident in this Landsat 7 July scene, note black arrows, terminus red arrow. The bare ice is a darker blue. The 300 meter thinning has left a sharp trimline beyond the current terminus marking the former ice height, that is well above the current fjord. This has resulted in a smaller accumulation zone. At the same time the retreat has reduced the calving rate as the terminus has narrowed and entered shallower water. The calving rate is related to water depth on these glaciers, Pelto (1991) . The reduced calving leads to a more positive mass balance, the increased snow line and reduce height of the glacier surface leads to reduced mass balance. This is equivalent to your bank account when you finish paying off your mortgage, but at the same time your income is declining. It will be interesting to observe the balance point of these two opposite forces. The University of Alaska Fairbanks began periodic altimeter surveys of the glaciers in the Sawyer Glacier region in 2000 and have noted a sharp decrease in surface elevation from the terminus to 1000 meters for the 2000-2009 period.