Glacier Outburst Triggers Floods, Closes Westside Rd. and Trails

On Aug. 13, a glacial outburst on the South Tahoma Glacier triggered a series of seven small debris flows—a  slurry of mud, boulders, trees and anything caught along the way—along Tahoma Creek and crossed the Westside Road.

No one was hurt, and the impressive Tahoma Creek Suspension Bridge remains standing, but there was some damage to the Westside Road. The road and area trails are closed to hikers at least through weekend while the park continues to monitor Tahoma Creek and assess damage to the road and area trails.

"This most recent glacial outburst and debris flow demonstrates again that Mount Rainier is a dynamic landscape,"said Randy King, Mount Rainier Superintendent. "Visitors should be aware of their surroundings when traveling in the park. Remember to remain alert for changes in water levels, unusual sounds or shaking of the ground. If you are near a river or stream, move quickly to higher ground."

A glacial outburst flood is a large, abrupt release of water from a glacier. According to the USGS, small flows are common at Mount Rainier during late summer and early fall; a second group of debris flows commonly develops from torrential rainfall during early winter storms. Between 1985 and today, more than 30 debris flows have rushed down the Tahoma Creek valley.

Avoid Westside Road and trails

The area remains potentially dangerous to hikers, and the temporary closure includes the following trails and routes. After the weekend, contact the park for closure information.

• Tahoma Creek Trail
• Westside Road
• Emerald Ridge - Tahoma Creek Loop
• The Westside Road approach to Gobblers Knob. (The other approach to Gobblers Knob is safe to hike.)
• Denman Falls via Westside Road

Mud flows common in glaciated volcano valleys

Debris flows—fast-moving slurries of boulders and mud—are sporadic events in the valleys of glaciated volcanoes due to the abundance of loose volcanic rock, excess water, steep slopes, and confining valley walls. These kinds of events are not uncommon at Mount Rainier, Mount Hood, Mount Baker or Glacier Peak.

“If you feel ground shaking and hear rumbling like an approaching freight train, get off the valley floor as quickly as possible, a debris flow can travel a lot faster than you can run,” recommended Carolyn Driedger, hydrologist and public information officer at the USGS Cascades Volcano Observatory in Vancouver, Wash., after a North Cascades debris flow along the Nooksack River a few years ago.

• Read the Mount Rainier release about the event

Flood cutting through debris field below glacier on Aug. 13. Photo by Scott Beason/NPS