Mount Rainier National Park approves expanded lahar detection system

CENTRALIA — The National Park Service has approved a proposal from the U.S. Geological Survey’s Cascades Volcano Observatory to improve the lahar detection system at Mount Rainier National Park.

Mount Rainier is an active volcano with a history of large lahars — volcanic mudflows — that have previously impacted now-populated areas in and outside of Mount Rainier National Park.

The USGS will now expand the existing volcano monitoring system inside the park. The project will increase the number of river drainages covered by the alert system to include the Tahoma Creek and Nisqually River valleys, which, along with the Puyallup River valley, are vulnerable to future landslide-caused lahars from Mount Rainier. Lahars can be triggered with or without a volcanic eruption, and lahars typically follow river drainages as they flow downstream from the sides of a volcano.

“The USGS and NPS worked together to identify how to best meet lahar detection and volcano monitoring needs at Mount Rainier National Park while protecting the character of the Mount Rainier Wilderness and the integrity of the park’s national historic landmark district,” said Greg Dudgeon, park superintendent. “This proposal not only supports public safety by providing communities more time to react to a lahar, but it also ensures protection of the resources that make Mount Rainier National Park such an extraordinary place.”

An environmental assessment (EA) was prepared and provided for public review and comment in 2021. The EA and signed decision notice and Finding of No Significant Impact (FONSI) are available on the project website at https://parkplanning.nps.gov/moralahardetection.

The selected alternative approves the installation of lahar detection equipment at nine locations. This equipment will allow rapid detection of lahars along drainages at risk of lahars triggered by landslides instead of volcanic eruptions. This project, once implemented, will help mitigate risk to people living adjacent to Mount Rainier by reducing the amount of time it takes for an alert to be sent out to potentially affected populations and communities after a lahar has been generated. The project also minimizes the size and extent of the lahar detection system in the Mount Rainier Wilderness and Mount Rainier National Historic Landmark District. Work to implement this decision is planned to begin later this year.

When lahars are detected or suspected, experts recommend getting to high ground as quickly as possible.

For more information on Mount Rainier National Park, visit www.nps.gov/mora.