Since mid-March, there have been a swarm of earthquakes under Mount St. Helens in Washington State, suggesting that the active stratovolcano is now recharging with magma.
According to the U.S. Geological Survey (USGS), over 130 vertical earthquakes ranging from low magnitudes 0.5 to 1.3 have been detected two to seven kilometres beneath the volcano’s crater. There are about 40 earthquakes at the volcano per week, and the occurrences are increasingly becoming more frequent.
“The magma chamber is likely imparting its own stresses on the crust around and above it, as the system slowly recharges,” reads a release by the USGS. “The stress drives fluids through cracks, producing the small quakes.”
Although it is a sign that the volcano’s plumbing system is slowly filling with magma, it does not mean another eruption is imminent. Volcanoes can recharge for many years without any eruption, just as what happened at Mount St. Helens from 1987 to 2004 leading up to the eruption of October 1, 2004.
As well, no release of anomalous gases or growth in the in the height of the lava dome have been detected.
Mount St. Helens experienced similar swarms of earthquakes in 2013 and 2014. It is considered the most active of the arc of Cascade Volcanoes, a series of 18 volcanoes stretching from Northern California to British Columbia.
In 1980, a major eruption event with a pyroclastic flow killed 57 people and destroyed 600 square kilometres of terrain. The volcano blew off the north face and top 400 metres of its peak in that single eruption.
Ash fall was significant to the extent that Vancouver, approximately 480 kilometres away, received a dusting by the next day.
The volcanoes nearest Vancouver are Mount Baker and Glacier Peak in Northern Washington State and Mount Garibaldi and Mount Cayley along the Sea to Sky Corridor. All four stratovolcanoes are believed to be active.