Monitoring Lahars at Mount Rainier
In response to the lahar-hazard concerns of local and State emergency-management agencies, USGS joined with them in 1995 to develop the Mount Rainier lahar-warning system in the Carbon and Puyallup River valleys in the southeastern Puget Sound region. The system comprises a detection component and a warning–dissemination component. Tens of thousands of people live in areas that may have as little as 40 minutes to as much as 3 hours to move to safety once a large lahar is detected, so the system must be robust, warnings must be disseminated promptly and widely, and people in harm's way must know how to respond to the warnings and take protective actions.
An automated system detects lahar flows by using a network of small sensors called acoustic flow monitors (AFMs) embedded underground to measure ground vibrations made by passing lahars. Computer base stations located in the Washington State Emergency Operations Center (EOC) continuously analyze signals from the field stations. Upon detection of a lahar, the computer alerts local 24–hour emergency monitoring and notification centers, who initiate the warning component of the system. Warning messages would trigger immediate, preplanned emergency-response actions.
Know how to respond to a lahar warning.
Residents, employees, and visitors in lahar–hazard areas will be notified of an approaching lahar through multiple channels of communication. Many schools and other public and commercial facilities will receive notice directly from the EOC, television and radio stations, as well as NO‘A‘ā Weather Radio, will broadcast warnings on the Emergency Alert System. A system of All Hazard Alert Broadcast (AHAB) sirens in cities and towns from Orting to the Port of Tacoma will provide evacuation alerts regarding the lahar and protective measures. Check with local officials to find out what is available in your community, school, or workplace.
Once people in the Puyallup and Carbon River valleys receive a lahar warning, they need to respond effectively. Pierce County and the State of Washington agencies have developed an evacuation plan with marked evacuation routes to aid residents and visitors. Parts of some communities rely on evacuation by foot to high ground, especially in areas where highways may become clogged with traffic.
In at-risk areas too remote to receive notification by one of the above methods, it is necessary to be aware of the natural warning signs of an approaching lahar—ground rumbling accompanied by a roaring sound similar to a jet or locomotive. Moving to high ground immediately is the recommended course of action.
The U.S. Geological Survey Cascades Volcano Observatory and the Pierce County, Washington, Department of Emergency Management were full partners in development and installation of the lahar–detection component of the warning system. Through a partnership arrangement, Pierce County Department of Emergency Management maintains and operates the lahar detection component with technical assistance from USGS. Pierce County also maintains and tests the siren notification system. The Washington Military Department's Emergency Management Division houses the base stations and local 24–hour emergency monitoring and notification centers are responsible for initiating notification of a lahar.