Earthquakes

Due to the eruptions of 1980-86 and 2004-2008, Mount St. Helens has had the best seismic monitoring network of all volcanoes in the Cascade Range. It is also the most seismically active volcanoes in the Washington and Oregon Cascades.

Mount St. Helens' high frequency of eruptions during the recent geologic past and its two eruptive episodes of the past three decades indicate a high probability of renewed eruptive activity.

Magma began intruding into the Mount St. Helens edifice in the late winter and early spring of 1980. By May 18, the cryptodome (bulge) on the north flank had likely reached the point of instability, and was creeping more rapidly toward failure.

New techniques for monitoring volcanoes and instruments that take advantage of new technologies are often employed by volcanologists when they are affordable and minimize exposure of personnel to hazards.