Mount Adams rock and snow avalanche, August 1, 2008

How did this not make the Seattle news? There was a major rock and snow avalanche from the cliffs above the Avalanche Glacier on the west side of Mount Adams, at 7:43 AM PDT on August 1, 2008:

daveslandslideblog.blogspot.com/2008/08/...-snow-avalanche.html
www.oregonlive.com/environment/index.ssf..._reshapes_mount.html

Major avalanche reworks Mount Adams
by Michael Milstein, The Oregonian
Wednesday August 06, 2008, 2:59 PM

A two-mile-long avalanche of ice and rocks large enough to rattle seismometers has reworked the southwest face of Mount Adams.

The volcano is usually very quiet, with few of the tremors that occur occasionally at other Cascade volcanoes such as Mount Hood. So the seismic signal from Mount Adams on Aug. 1 stood out to Cynthia Gardner of the Cascades Volcano Observatory in Vancouver, who first noticed it. "It is a very large signal at a volcano that has a very quiet background," she told The Oregonian on Wednesday.

She passed on her observations to researchers at the Pacific Northwest Seismic Network at the University of Washington. There, seismologist Robert Norris recognized it as the likely signature of a major avalanche or rockfall, Norris said. He relayed the information to Darryl Lloyd, a Hood River photographer and longtime authority on the Mount Adams region. Lloyd reported back that indeed a major avalanche beginning at Avalanche Glacier had tumbled about two miles down the mountain.

The Avalanche Glacier area of the mountain is aptly named, as it has released major avalanches in the past. A rock-and-ice avalanche from the same area in August 1997 ran about three miles down the mountain. It contained an estimated 5 million cubic meters of material and was the largest avalanche in the Cascades since one on Mount Rainier in 1963, according to the Cascades Volcano Observatory. The avalanche this month was not that big, Lloyd said. It was more akin to a 1983 avalanche from the same area.

. . .

That looks pretty big to me. Sounds like the snowpack was weighing down on that volcanic kitty litter.

Spicoli,

Actually, from what I've seen there seems to be less snow on the upper mountain over the last several years than I'm used to seeing. Amar is well informed on things like this, so maybe he could add to it, as I'm just going from personal experience.

Thanks for the avi story though. Wasn't there a large one on the Klickitat several years ago? I remember that one being very big...

I'm pretty sure the Klickitat one happened in 1997, and that's probably the one they are referring to "in the same area". I do remember that one, but I don't remember hearing about any on the Avalanche glacier.

Actually, 1997 had two entirely separate and very large rock avalanches on Mount Adams: August 31, 1997, on the Avalanche Glacier, and October 20, 1997, on the Klickitat Glacier:

vulcan.wr.usgs.gov/Volcanoes/Adams/Debri...l1997/framework.html

And in answer to Spicoli and Jason, I don't know what (if any) effect the snowpack this year might have had on this avalanche. My gut feeling, totally unsubstantiated as of yet, is that this avalanche was caused by the failure of an oversteepened rotten cliff of hydrothermally-altered clay, just like most other major rock/debris avalanches on the Cascade volcanoes. I'm planning to head down there to take some close-up photos within the next few days, but the real cause of this avalanche will likely remain unknown/unstudied in this case.

Pretty fascinating power by the 97 and present slides.
The picture of that the USGS has of the mountain in 97 shows an amazing amount of snow in the SW chutes for a Sept-