CASCADES VOLCANO OBSERVATORY WEEKLY UPDATE
Friday, March 18, 2016 4:30
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN
Activity Update: All volcanoes in the Cascade Range of Oregon and Washington are at normal background levels of seismicity. These include Mount Baker, Glacier Peak, Mount Rainier, Mount St. Helens, and Mount Adams in Washington State; and Mount Hood, Mount Jefferson, Three Sisters, Newberry, and Crater Lake in Oregon.
Recent observations: Over the past week, earthquakes have been located at Mount Rainier, Mount St. Helens and Mount Hood. At Mount St. Helens, there have been over 100 very small earthquakes, too small to be formally located, all likely occurring between 2 and 4 kilometers depth under the volcano. Such activity is consistent with what we understand to be background levels of seismicity at Mount St. Helens.
The seismic network at Mount St. Helens continues to detect small magnitude earthquakes. Since March 14, 2016, twelve earthquakes have been formally located and the local 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, at an average depth of about 3-4 km. According to the Pacific Northwest Seismic Network, the largest earthquake over a four-day period has been 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 slow re-pressurization of the magma reservoir, similar to what occurred after the 1980-1986 eruption. This is to be expected and it does not indicate that the volcano is likely to erupt anytime soon.
March 19, 2016. Cascade Range , United- States of America :
Source : USGS
Photo: Blog scentifiqueamericain.