Mount St. Helens Seismic Activity

Recent reports from the US Geological Survey (USGS) have drawn attention to a series of earthquakes occurring beneath Mount St. Helens, raising questions about the volcanic activity in the region.

Unprecedented Earthquake Activity

  • Since mid-July this year, approximately 400 earthquakes have been documented under Mount St. Helens.
  • This sequence of tremors is considered the longest since the volcano’s last eruption in 2008.
  • Concerns arise, but there are currently no signs of an imminent volcanic eruption.

USGS’s Statement

  • The USGS addressed the situation in an update on its website, acknowledging the uptick in earthquakes.
  • Most of the recorded earthquakes are small, measuring less than M1.0, and are not felt at the surface.
  • The USGS emphasized that there is no immediate cause for alarm, as ground deformation and gas emissions remain within normal (green) background levels.

Monitoring by the Pacific Northwest Seismic Network (PNSN)

  • The Pacific Northwest Seismic Network has been actively monitoring earthquakes and volcanic activity in the region.
  • Since mid-July, they have identified over 400 earthquakes, with approximately 30 earthquakes located per week recently.
  • This contrasts with the period since 2008 when only an average of 11 earthquakes were recorded per month at Mount St. Helens.

Historical Context

  • The catastrophic eruption of Mount St. Helens in 1980 resulted in 57 fatalities and widespread devastation.
  • The eruption, triggered by a 5.1 magnitude earthquake, led to the largest landslide in recorded history.
  • While the current earthquake activity is concerning, it is essential to differentiate between past events and the present situation.

Magnitude and Sensitivity

  • Most of the recent earthquakes, occurring over a three-month period, have a magnitude of less than 1.0.
  • These small-magnitude tremors are generally not perceptible at the surface.
  • According to Wes Thelen, a volcano seismologist, these minor earthquakes may indicate magma movement and “recharging” of the volcano’s underground chambers and cracks.



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