On March 14, 2016, the seismic network at Mount St. Helens began detecting small magnitude earthquakes at a depth of 3–4 km beneath the crater. Twelve earthquakes have been formally located and the local seismic network detected at least 100 earthquakes too small to be recorded on enough seismometers to calculate a location. Many of the earthquakes have similar seismic signatures, suggesting they are occurring in the same area as the located earthquakes. According to the Pacific Northwest Seismic Network, the largest earthquake over a four-day period was a Magnitude 0.7, an event that would not be felt even if you were standing on the surface above it.
These types of volcano-tectonic earthquakes beneath Mount St. Helens are likely associated with the recharge of the volcano. After the 2004-2008 eruption, subtle inflation of the ground surface and seismicity indicate that the magma reservoir beneath Mount St. Helens is slowly re-pressurizing, as it did after the conclusion of the 1980-1986 eruption. This is to be expected and it does not indicate that the volcano is likely to erupt anytime soon. Re-pressurization of a volcano's magma reservoir is commonly observed at volcanoes that erupted recently, and recharge can continue for many years without an eruption. For more information, see the Activity Updates for Volcanoes in CVO Area of Responsibility and Earthquake Monitoring at Mount St. Helens.
Join us July 25–29, 2016, for a 5-day educator workshop at Mount Rainier. The workshop features informative talks on Cascade volcanoes and volcanic processes, ideas for classroom activities, hikes into the field, and tips for organizing school field trips to visit the volcano. There is no charge for this workshop and camping is available to participants. Registration information is at the Mount Rainier Teacher Professional Development webpage.
A new geologic map and pamphlet provides information on a young volcanic field of intraplate basalts located just east of the Cascade Arc—the Simcoe Mountains volcanic field, in south-central Washington State.
The map shows, in various colors, the areas covered by 223 different eruptive units, mostly lava flows and cinder cones ranging in age from ~4 million to 600,000 years old. Most of these units were produced by short-lived (a few years) basaltic eruptions that featured localized lava fountains and/or lava flows that extended at most several miles, creating small volcanic cones that are now extinct. The only large long-lived volcano in this field capable of erupting again in the future is Mount Adams, located on the western boundary.
Read more in Scientific Investigations Map 3315, Geologic Map of the Simcoe Mountains Volcanic Field, Main Central Segment, Yakama Nation, Washington. This product was produced by USGS on behalf of the Water Resources Program of the Yakama Nation.