USGS pressing for expansion of lahar detection sites around Mount Rainier | KNKX

USGS pressing for expansion of lahar detection sites around Mount Rainier

Oct 20, 2020

Officials from the U.S. Department of the Interior and United States Geological Survey have been touring sites in Mount Rainier National Park this week. They’re looking at five new locations where upgraded monitoring stations will soon enhance detection of lahars. There’s also a proposal to add another 12 lahar monitoring stations in the park, to complete an expansion they say will put detection at Rainier on par with other high-threat volcanoes in the region, such as Mount St. Helens.

Lahars are potentially devastating high-speed mudslides that are triggered by volcanic activity, as heat from inside the cone heats up snow and ice. The expansion will add real-time capability to collect and transmit seismic, acoustic, visual and physical data, so that accurate warnings could go out as soon as worrisome activity is detected.

"In the case of earthquakes, we have literally hundreds of sensors that allow us to get a very good signal. And that’s why we’re pushing right now to get these installations out on Rainier as quickly as possible,” U.S. Geological Survey Director Jim Reilly said while touring the park.

When the expansion is complete, he says there will be a total of 35 detection sites surrounding the volcano. “The more sensors you have, the better the quality of the signal."

In additon to increased numbers, upgraded technology including machine learning will enhance the system and make it more effective.

A public comment period is currently open on the proposal for the additional 12 monitoring stations inside the park.

The last major lahar to come off the mountain was 500 years ago, around 1500 BC. But park officials say new data indicate hazards that could affect communities in the valleys beneath the mountain at any time.

Of particular concern, says Seth Moran, the USGS scientist in charge at the Cascades Volcano Observatory, are areas of Rainier where prior volcanic activity has taken place and left cracks in the mountainside. He says research in the late 1990s and early 2000s points to some areas of concern.  

“That work showed that the West Flank still has a fair amount of altered rock in it that goes a little inside the volcano,” he said.  “And that, combined with the steepness of it…that is the one side of the volcano where spontaneous landslides could conceivably happen.”

A spontaneous landslide is one that is not triggered by obvious volcanic activity, leaving far less time for communities to evacuate. And the West Flank looms over south Puget Sound and the most populated areas near the mountain.

Moran says the good news is that, at Mount Rainier, only one of the nine lahars that have taken place over the past 5,600 years has been a spontaneous one. It also was the most recent one: the Electron Mudflow, estimated to have taken place 500 years ago, in approximately 1500 AD.

So, the odds are against a spontaneous lahar, but Moran says you can’t mitigate the risk without a warning.

The expansion of the lahar detection and early warning system is the first in over a decade.  It has been enabled by the omnibus public lands package known as the John D. Dingell Jr. Conservation, Management, and Recreation Act that passed in March 2019.