By Dave Tucker; October 6, 2010
On or shortly before September 3, 2010, a large ice avalanche slid from the east face of Sherman Peak. The slide involved the full thickness of ice, and scoured the fragmental rock surface beneath. The resulting mix of ice and saturated rock formed a slushy debris flow which descended the Boulder Glacier for about 3600 vertical feet, petering out at about 6400 feet, well above the ice terminus.
Alert reader Jason Griffith noted and photographed the debris on the surface of the glacier on September 3, from the Anderson Lakes trail across Baker Lake. When the gas sampling was being done in Sherman Crater in early August, we noted that bergschrund at the source area near the summit of Sherman Peak was conspicuously wide; the entire slope had an ominous appearance.
Debris flows beginning in the same location as this one are not uncommon. A much larger debris flow occurred in 2006. Scroll down at the MBVRC main website’s “images” page to see photos of that one. There is also a link on that page to John Scurlock’s dramatic aerial photos of that debris flow. A paper (Frank and others, 1975) was published quantifying on these phenomena. The cause may simply be gravity, acting on this steep slope once enough snow has accumulated following the previous event. However, hydrothermal activity may be responsible as well.
Frank, D., Post, A. and Friedman, J.D., 1975, Recurrent geothermally induced debris avalanches on Boulder Glacier, Mount Baker, Washington; Journal of Research, US Geological Survey, v. 3 n. 1, pp. 77-87