7 August 2008

Mount Adams rock and snow avalanche

Posted by Dave Petley

The online site Oregon Environmental News has today carried a rather nice article on a new, large, rock and snow avalanche on Mount Adams (Fig. 1) in the Cascade Range in Washington State. Mount Adams is a stratovolcano that has a long history of such events. Many readers will be aware for example of the 31st August 1997 event, which had a volume of about 5 million cubic metres, and is well documented by the USGS.

Figure 1: Google Earth view of the southwest face of Mount Adams, upon which the most recent event occurred.

This event was first picked up at about 14:50 UT on 1st August at the seismometers at the Cascades Volcanic Observatory, who have kindly put the seismic record online (Fig. 2).

Figure 2: Seismic record from the Cascades Volcanic Observatory showing the 1st August 2008 rock and snow avalanche on Mt Adams (click on the image for a better view).

The seismologists quickly recognised that this event was not volcanic in origin, but was in fact associated with a mass movement. As a result, they contacted a local photographer, who went up there and confirmed that a rock and snow avalanches about 2 miles (3 km) has occurred. H.C Tupper has been able to collect a photograph of the event (Fig. 3).

Figure 3: H.C Tupper’s’s photograph, posted on Oregon Environmental News, of the 1st August 2008 Mt Adams rock and snow avalanche. Note the annotation is from the source and is thus not by me (click on the image for a better view).