Glacial outburst forces closure of Westside Road at Mount Rainier

A torrent of water and debris from a glacial outburst Thursday flows under a suspension bridge near Indian Henry's Hunting Ground at Mount Rainier National Park.
A torrent of water and debris from a glacial outburst Thursday flows under a suspension bridge near Indian Henry's Hunting Ground at Mount Rainier National Park. Courtesy

A glacial outburst Thursday sent a torrent of rocks, trees and debris 4 miles down Tahoma Creek, damaging and forcing the closure of Westside Road and Tahoma Creek Trail at Mount Rainier National Park.

The road and trail will be closed at least through the weekend as park staff members watch for additional flows and assess damage to the road and area trails, park superintendent Randy King said.

“I’m sure during the weekend, there will be more surges coming out of this, especially if we get any kind of significant rain event,” park geologist Scott Beason said.

The outburst began about 9:40 a.m., Beason said, based on seismic recordings and reports from park staff and visitors in the area. It was followed by a series of pulses.

“A lot of people reported large noises in the morning. But something happened at 11:30 (a.m.), that was the biggest and longest event, which led to the debris flow people saw in the creek about noon,” he said.

Some of the trees carried downstream by the flow were at least 50-feet long.

Carolyn Driedger, a hydrologist at the U.S. Geological Survey’s Cascades Volcano Observatory in Vancouver, Washington, said the outburst was one of the largest seen on the southwest flank of Mount Rainier.

After observing the scene during a helicopter flight Thursday afternoon, Beason said it looks as though the outburst was caused by a 0.5-acre chunk of the terminus of the South Tahoma Glacier breaking away, releasing the torrent of water.

Beason said it appears a 300- to 400-foot section of the glacier has become disconnected from the rest.

“I’m thinking there was a water buildup in there because we’ve had such a hot summer,” he said. “I think the water built up enough that it gave way at the foot of the glacier. It is a really steep terminus, there are claws and teeth of ice just sitting up waiting to fall.”

Minimal damage was done to the road above the parking area, but Beason said the Tahoma Creek Trail likely has been damaged in multiple locations.

Some water came across Texas Crossing and into Fish Creek, Beason said. That is the first time that has happened since 2006.

Debris flows are not uncommon in the Tahoma Creek valley. Since 1985, more than 30 debris flows have occurred.

August 13, 2015 Debris Flow on Tahoma Creek, Mount Rainier Nat...

Here is video footage of the August 13, 2015 debris flow at Mount Rainier. Zachary Jones and Caroline Pedro were walking up the now closed Westside Road towards the Tahoma Creek Trail when they heard a loud rumbling. Zachary asked Carol what the sound was, she thought it might be a passing train. They kept walking and got to a clearing where they had a full view of Tahoma Creek. In the distance, they saw huge mounds of tree debris and boulders raging down the creek. Zachary said if we're gonna die, we might as well film it! [Note: both are okay!]

Posted by USGS Volcanoes on Friday, August 14, 2015

Jeffrey P. Mayor: 253-597-8640