CASCADES VOLCANO OBSERVATORY INFORMATION STATEMENT
U.S. Geological Survey
Monday, October 30, 2023, 3:53 PM PDT (Monday, October 30, 2023, 22:53 UTC)

MOUNT ST. HELENS (VNUM #321050)
46°12' N 122°10'48" W, Summit Elevation 8363 ft (2549 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN

Summary:  Over the past three months, seismicity at Mount St. Helens has been elevated but remains consistent with background seismicity. Most of the earthquakes have been less than magnitude 1.0 and too small to be felt at the surface. No significant changes have been observed in other monitoring parameters and there are no signs of an imminent eruption.

There is no change in Volcano Alert Level or Aviation Color Code at this time. Mount St. Helens remains at normal, background levels of activity.

Current Observations

At Mount St. Helens, over 400 earthquakes have been located by the Pacific Northwest Seismic Network since July 15, 2023. In late August to early September, about 40-50 earthquakes were located per week, and more recently, the number has been about 30 located earthquakes per week. To compare, since 2008, on average about 11 earthquakes have been located per month at Mount St. Helens.

The largest earthquake in this recent period was a magnitude 2.4 that occurred on August 27, 2023. Most of the events have been less than a magnitude 1.0. Earthquake depths are between 2 and 6 km (1.2 and 3.7 miles) below sea level, which is approximately 4 to 8 km (2.5 and 5 miles) below the crater floor.

No changes have been detected in ground deformation, volcanic gas or thermal emissions at Mount St. Helens. No changes have been observed at other Cascade Range volcanoes.

Prognosis

Short-term increases in earthquake rates are common at Mount St. Helens and are considered part of the background seismicity. The current seismicity represents the largest short-term increase in earthquake rates since the last eruption ended in 2008. However, longer duration sequences with more events occurred in 1988-1992, 1995-1996 and 1997-1999.  None of the sequences in the 1980’s and 90’s directly led to eruptions.  

Small magnitude earthquakes located beneath Mount St. Helens at depths well below sea level are generally thought to be associated with pressurization of the magma transport system.  One cause for this pressurization is the arrival of additional magma, a process called recharge. Mount St. Helens is fed by magma that forms near the base of the crust at depths of about 25 km (~16 miles). Magma slowly rises through the lower crust and accumulates in a reservoir about 4‒10 km (~2.5‒6 miles) below sea level. Recharge events can occur when magma enters this upper reservoir and increases stresses that lead to earthquakes.

High rates of seismicity, interpreted as recharge, have been observed in the past at Mount St. Helens and at other volcanoes and can continue for many years without an eruption.

Potential hazards

There have been no significant changes in hazards at Mount St. Helens as a result of this activity.

Current monitoring

The USGS monitors volcanoes with instrument networks and satellites; conducts research on volcano processes; and communicates important information to the public to mitigate risk and safeguard society.  The USGS Cascades Volcano Observatory jointly operates the monitoring network at Mount St. Helens with the Pacific Northwest Seismic Network (https://pnsn.org/)

The U.S. Geological Survey Cascades Volcano Observatory and the Pacific Northwest Seismic Network continue to monitor Washington and Oregon volcanoes closely and will issue additional notifications as warranted.

Website Resources

Mount St. Helens history and hazards: https://www.usgs.gov/volcanoes/mount-st.-helens

Current Mount St. Helens seismicity: https://pnsn.org/volcanoes/mount-st-helens#seismicity
For seismic information on Oregon and Washington volcanoes: http://www.pnsn.org/volcanoes
For information on USGS volcano alert levels and notifications: https://www.usgs.gov/programs/VHP/volcano-notifications-deliver-situational-information

Subscribe to these messages: https://volcanoes.usgs.gov/vns2/

CONTACT INFORMATION:

Jon Major, Scientist-in-Charge, USGS Cascades Volcano Observatory, jjmajor@usgs.gov, 360-993-8927

Wes Thelen, Geophysicist, USGS Cascades Volcano Observatory, wthelen@usgs.gov, 360-993-8977

Liz Westby, Geologist, USGS Cascades Volcano Observatory, lwestby@usgs.gov, 360-993-8979