Glacial outburst floods at Mount Rainier

From National Park Service

A glacial outburst flood is a large sudden release of water from a glacier. These are common in Iceland where they are known as Jokulhlaups (o with an umlaut that I can't do in a blog). Here is a link to an impressive video of one in 2010 during the active phase of Eyjafjallajokull.

From The Olympian

On Thursday afternoon, August 14, about a half acre of the South Tahoma Glacier on Mount Rainier broke off, triggering a series of outburst floods. The Rainier outbursts were very very small by Icelandic standards, but at least one was fortunately captured on video. A park volunteer heard a "loud roaring sound, followed by the sounds of water moving boulders and the cracks of breaking trees." Fortunately, that volunteer and another nearby were able to get to high ground, from which they observed the outburst stages. Debris flows were reported at 9:40 a.m., 10:30 a.m., 11:30 a.m., and 12:40 p.m. The 11:30 event generated a debris flow that reached the Westside Road at noon. The road was sufficiently damaged that it will be closed for the weekend. In total, seven waves of debris were recorded.  The debris ended up in Tahoma Creek valley. The Nisqually River saw a 0.5 foot rise during the afternoon. Since 1980 more than 30 debris flows have been recorded from the South Tahoma Glacier. Hot dry weather and/or heavy rainfall trigger the events.