Mt. St. Helens volcano (Washington): small earthquake swarms no signs of worries
The recorded quakes have been at shallow depths between 2-7 km under the summit and ranged in magnitudes from 0 (or less) to 3 on the Richter scale, i.e. they are all tiny. Only rarely, they exceeded magnitude 2 and only a very few might have been felt by persons being very close.
USGS volcanologists and seismologists interpret the vertical area where these quakes occurred as the area where a small amount of fresh magma has been rising into the volcano's plumbing system (a magma chamber). Magma rises, pressurizes surrounding rock to make space and causes fracturing = tiny quakes.
The current swarm is only one of a series of similar swarms that have taken place since 1988, including some much more energetic ones (such as during 1998-99). Most such earthquake swarms, not only at Mt. St. Helens, but at almost any volcano, are NOT followed by eruption, or at least not immediately. In the case of Mt. St. Helens, the large earthquake swarm during 1998-99 preceded the small effusive activity during 2004-2008 by 5 years.
For the time being, USGS keeps the volcano at alert level green (=normal); the observed seismic activity is too small to justify a raise in alert and is best seen as part of the normal activity during a dormant phase of the volcano. When the volcano will erupt again (it is almost certain that it will), is impossible to predict on the basis of these quakes alone. It might be years or even centuries.
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