What If Part of Mount Rainier Collapsed?

No eruption required.

Nepal Showed Us What's Possible

The trigger

A glacier collapse triggered a catastrophic debris flow. Could a cascading ice, rock, and mud event happen here?

The setup

Huge steep glaciers. Volcanic rock weakened by hydrothermal activity deep inside the mountain.

It happened before

260M m³ Volume of the Electron Mudflow A flank collapse that became a major lahar

How it happens

The modeled path

USGS modeling routes an Electron-scale west-side lahar down the Puyallup toward Orting.

At Orting

~60 min Modeled arrival time at Orting lowlands Modeled flow front: ~13 ft deep, ~9 mph

The lahar would continue toward Sumner and Puyallup. Seattle is not in a direct lahar pathway.

Alternate scenario

~20 min Ashford Tahoma Glacier headwall collapse reaches the town of Ashford

~50 min Alder Lake Lahar reaches Alder Lake — enough modeled material to overtop the 330-ft Alder Dam

What we don't know

The model showed overtopping potential at Alder Dam. USGS did not model what happens downstream. We don't claim the dam fails.

Warning systems

Sensors and siren systems are in place. Warning time is short — but it exists.

The insight

The most dangerous thing Mount Rainier could do may not be erupt.

Learn about Rainier's lahar zones. Know your evacuation route.

Explore USGS Lahar Hazard Maps