MOUNT St Helens is drumming out a warning beat. Regular, repetitive earthquakes around the volcano are being triggered by the movements of a rock plug, reverberating in the neck of the volcano.
In October 2004 a small eruption on Mount St Helens in Washington state was accompanied by a swarm of minor earthquakes, approximately one every half minute. The tremors have continued at the rate of around one every six minutes.
By modelling the volcano, Richard Iverson of the Cascades Volcano Observatory in Vancouver, Washington, and his colleagues conclude that the most likely explanation for these unusually regular drumbeat earthquakes…
