Glacier Slides Down Mount Adams

A three-mile-long debris avalanche ripped down the southwest flank of Mount Adams over the Labor Day weekend, creating a scar than can be seen easily from Portland.

The avalanche appears to be the largest on the mountain since the great slide of 1921, according to author Darryl Lloyd in a story published in Pack & Paddle Magazine.

The Labor Day weekend slide surpasses the size of a similar slide in July, 1983.

The slide apparently was triggered by rockfall at the head of Avalanche Glacier, near the 12,000-foot elevation of the 12,276-foot peak. The entire glacier tore apart and fell almost 6,000 feet, spilling into the timberline area.

One lobe of the slide stopped about a quarter-mile above the popular Round-the-Mountain trail near Salt Creek.

The source of the slide is the steep, crumbling part of the main cone consisting of hydrothermally altered rocks, rich in clay minerals that are prone to failure.

Scientists have estimated that about a million cubic yards of altered rock came down in the slide, in addition to an untold amount of glacier snow and ice.