The Cascades Volcano Observatory (CVO) issued an information statement about seismicity at Adams. In the month of September six locatable earthquakes with magnitudes of 0.9-2 were recorded by one seismic station located 11 km SW of the summit and others located much farther away. Typically, at Adams, one earthquake is recorded every 2-3 years. CVO noted that there was no indication that the earthquake activity was a cause for concern; the Volcano Alert Level remained at Normal (the lowest level on a four-level scale) and the Aviation Color Code remained at Green (the lowest color on a four-color scale). CVO together with the Pacific Northwest Seismic Network (PNSN) plan to install temporary seismic stations in the 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.

Geological Summary. The andesitic-dacitic Mount Adams stratovolcano is second in volume only to Mount Shasta in the Cascade Range. The volcanic complex is elongated along a NNW-SSE line, and includes more than 60 flank vents over 200 km2. Volcanism began about 940 ka, with three main cone-building stages occurring at about 500, 450, and 30 ka. It was active throughout the Holocene, producing two dozen minor explosive eruptions from summit and flank vents. Six Holocene lava flows are located on the flanks between 2,100 and 2,600 m elevation. The most voluminous Holocene lava flows, some of which traveled 10 km or more, were emplaced between about 7,000 and 4,000 years ago. The latest eruption about 1,000 years ago produced a minor tephra layer and possibly a small lava flow down the E flank.

Source: US Geological Survey Cascades Volcano Observatory (CVO)