Adams

In September, the U.S. Geological Survey Cascades Volcano Observatory (CVO) and Pacific Northwest Seismic Network (PNSN) located six earthquakes at Mount Adams, ranging from magnitudes 0.9 to 2.0. Typically, earthquakes at this volcano are located at a rate of about 1 earthquake every 2-3 years. With just one seismic station near the volcano, monitoring capabilities are currently limited. CVO and PNSN plan to install temporary seismic stations in the Mount Adams area, which will allow detection of smaller earthquakes and better estimates of size, location, and depth, information necessary to assess the significance of the activity. Currently, there is no indication that the level of earthquake activity is cause for concern, and the alert level and color code for Mount Adams remain at GREEN / NORMAL. CVO and the PNSN will continue to monitor earthquake activity and release further updates as the situation warrants.

RECENT ACTIVITY

Six locatable earthquakes (magnitude 0.9–2.0) were detected in September on seismic station ASR2, a PNSN-operated station located about 7 miles (11 km) southwest of the summit of Mount Adams, as well as other stations much farther away from the volcano. This represents the most earthquakes located at Mount Adams in a month since monitoring began in 1982.  No earthquakes were felt at the surface. The locations and depths are not well constrained due to the sparse Mount Adams seismic network, and smaller earthquakes have occurred that seismologists have been unable to locate.

Satellite imagery does not show any detectable ground deformation at the volcano. Mount Adams does not have a dedicated volcanic gas sampling program. 

WHAT WE ARE DOING

To improve seismic monitoring capabilities, CVO has permission from the U.S. Forest Service to install temporary seismic stations south and southwest of Mount Adams. The seismic stations are part of CVO’s rapid deployment instrument packages that can be deployed quickly as needed.

Data from the new temporary stations will be transmitted in real-time to CVO and PNSN along with data from the existing permanent station. This will improve our ability to locate smaller earthquakes with more certainty and assist in understanding the cause of these earthquakes. The results of our findings will determine if any additional actions are needed. 

MORE INFORMATION ABOUT MOUNT ADAMS AND ITS HAZARDS

Mount Adams in south-central Washington is about 50 miles (80 km) west-southwest of Yakima, Washington, and 30 miles (55 km) north of the White Salmon-Hood River area of Washington and Oregon along the Columbia River. Mount Adams is the most prominent summit along the north-south trending Mount Adams-King Mountain volcanic field, which includes more than 120 smaller volcanoes located in parts of Skamania, Lewis, Klickitat, and Yakima counties, and the western part of the Yakama Nation.

Mount Adams is the second tallest volcano in Washington State and is the state's largest active volcano in both area and volume. Typical behavior of Mount Adams has been primarily effusive (lava flows) and seldom explosive. The few downwind ash layers it has produced in the last 12,000 years are small in volume and limited in extent. Over the last 12,000 years, there have been four lava flows originating on the apron of the volcano and two vents along its south ridge. The lava flows have typically travelled only a few miles from their vents. The last volcanic eruption occurred between 3,800 and 7,600 years ago.

The greatest threat to people living near Mount Adams are lahars (muddy flows of rock, ash, and ice that surge downstream like rapidly flowing concrete) that could occur during eruptive or noneruptive periods. About 6,000 and 300 years ago, lahars generated by landslides of weakened rock high on the southwest side of the volcano flowed as far as the Trout Lake area and beyond. Much smaller landslide-triggered avalanches of altered rock and snow from the headwall above the Avalanche Glacier on the southwest side of the summit block occurred as recently as 1921 and 1987 but did not travel more than a few miles. The ice-capped summit conceals large volumes of hydrothermally weakened rock, and future landslides of this weakened rock could generate far-traveled lahars.

The USGS national volcanic threat assessment ranked Mount Adams as a high-threat volcano. The threat-potential assessment takes into account both volcano hazards and community exposure. Hazards are derived from what is known about the recency and style of previous eruptions and exposure factors include impacts on nearby population, aviation activity, and infrastructure during a volcanic event. The USGS, through its Cascades Volcano Observatory, is working to improve monitoring capabilities at high- and very-high threat volcanoes in the Cascade Range through network expansion vital to the National Volcano Early Warning System authorized in 2019.

RESOURCES

Mount Adams eruption history: https://www.usgs.gov/volcanoes/mount-adams/science/eruption-history-mount-adams

Mount Adams debris avalanches and lahars: https://www.usgs.gov/volcanoes/mount-adams/science/debris-avalanches-and-lahars-mount-adams

2018 Update to the U.S. Geological Survey National Volcanic Threat Assessment: 2018 Update to the U.S. Geological Survey National Volcanic Threat Assessment (usgs.gov)

Pacific Northwest Seismic Network: https://pnsn.org/ 

The U.S. Geological Survey Cascades Volcano Observatory and the University of Washington Pacific Northwest Seismic Network continue to monitor Washington and Oregon volcanoes closely and will issue additional notifications as warranted.

Website Resources

For images, graphics, and general information on Cascade Range volcanoes: https://www.usgs.gov/observatories/cvo
For seismic information on Oregon and Washington volcanoes: http://www.pnsn.org/volcanoes
For information on USGS volcano alert levels and notifications: https://www.usgs.gov/programs/VHP/volcano-notifications-deliver-situational-information

Jon Major, Scientist-in-Charge, Cascades Volcano Observatory, [email protected]

General inquiries: [email protected]