Packs for Survival Blog

Early this morning January 25, 2012 about 10:51 UTC (02:51 local time) the ground near Mt. St. Helens began to shake. The earthquake a magnitude 3.4, had an epicenter 10 miles NNW of the volcano. Several small aftershocks followed over the next hour. This series of small earthquakes occurring in approximately the same area over a short period of time is called an earthquake swarm. Earthquake swarms are common around volcanoes, and in some cases can be a precursor to an eruption.

According to the USGS, seismic activity around volcanoes can be produced from tectonic or volcanic activity. Tectonic type earthquakes around volcanoes occur when rocks break along the faults or fractures. Seismologists’ task is to determine if these earthquakes are volcanic or tectonic. This will help establish if there is a risk of eruption, or if it’s just the mountain becoming restless.