By Dave Tucker; October 6, 2010
The 2010 slushy debris flow descended the Boulder Glacier to about 6200'. Jason Griffith photo.
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.
The bergschrunds in the steep snow slope just below the summit of Sherman Peak is the source for the ice avalanche-debris flows that sweep the Boulder Glacier. This photo was taken inside Sherman Crater August 12, 2010. John Scurlock photo.
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.
Reference:
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
Mount Baker Volcano Research Center subscription website 
Dave, while helping Melissa on her Sherman Crater study this past summer, my ropemate Braden Zwade and I climbed halfway up the slope just to the right of the ‘schrund where the failure occurred. I can’t imagine what our our pulse rate would have been if it had slid while we were mere yards away! Sometimes one can be at the right place (or wrong place) at the right time, sometimes the opposite is true.
By: Doug on October 6, 2010
at 14:07
Knowing what I do about the potential on this slope, I don’t go anywhere near it now! It is, on the face of it [no pun intended]. a good looking line to the summit of Sherman Peak if you are in the crater, or have just dipped in over the south rim.
By: magmatist on October 6, 2010
at 14:35