Washington’s scorching weather causes lahar on Mt. Rainier

17 August 2023

Washington’s intense bout with record-breaking temperatures likely triggered a glacial mudslide on Mount Rainer.

Monitors registered the lahar Tuesday afternoon, saying it lasted for hours.

On Aug 15, a small glacial outburst transitioned to a debris flow in @MountRainierNPS. Flow remained in remote upper reaches of Tahoma Creek drainage (no damage). Event detected by #USGS lahar monitoring stations, like TABR. Strongest signal occurs as flow front passes. pic.twitter.com/F4GHbRoBPY

— USGS Volcanoes🌋 (@USGSVolcanoes) August 16, 2023

What are lahars?

Lahars, “along with debris flows and debris avalanches, are masses of rock, mud and water that travel rapidly downslope and downstream under the action of gravity,” the Cascades Volcano Observatory via the U.S. Geological Survey (USGS) says.

“Volcanoes are a perfect setting for these events because of an abundance of steep, rocky rubble and a ready source of water in the form of rain, snow or ice, the observatory added. “Lahars can flow many miles downstream from the volcano, making this the most threatening hazard in the Cascades.”

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Federal geologists believe the South Tahoma glacier released a burst of water, starting a slide that ran under the Tahoma Creek Bridge on Nisqually-Paradise road. The lahar’s path is still visible on the Southwest side of Rainier. This lahar is considered “small.”

Lahars can occur by rapid melting of snow and ice during eruptions, by liquefaction of large landslides (also known as debris avalanches), by breakout floods from crater lakes, and by erosion of fresh volcanic ash deposits during heavy rains, the observatory notes.

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Potential community effects of lahars

Lahars and excess sediment can cause serious economic and environmental damage to river valleys and flood plains, according to the USGS. Large lahars can crush, abrade, bury, and carry away almost anything in their paths. Buildings and valuable land could be partially or completely buried. USGS described large lahars as “rivers of concrete.”

Lahars and pyroclastic density currents (or flows) have been responsible for almost 40% of all fatalities related to volcanoes, according to Forbes.

A fire ban for Mount Rainier National Park will also be in place starting Friday, barring all campfires and the use of fire pits or barbecue grills. Portable stoves and lanterns that can use bottled fuel and be turned off are still allowed.

The ban comes as much of Western Washington is dealing with various levels of drought, making the region more susceptible to wildfires.

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