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M3.9 earthquake and swarm occur at Mount Hood on June 5, 2021

June 5, 2021

The M 3.9 earthquake occurred at a depth of 2.7 miles below sea level. At this time, seismologists do not believe the earthquake swarm signifies a change in volcanic hazard at Mount Hood, and will continue to monitor the swarm and issue updates as the situation warrants.

At 20:51 PDT on June 5 (0351 UTC on June 6) a Magnitude 3.9 earthquake occurred about 2.5 mi (~4 km) south of the summit of Mount Hood, Oregon, at a depth of 2.7 mi (4.3 km) below sea level. The earthquake was felt in areas around Mount Hood.

The swarm was preceded by several earthquakes in the hour prior to the M 3.9, and tens of aftershocks have occurred with event rates declining in a manner typical of mainshock-aftershock sequences. The mainshock characteristics and location are consistent with past swarms in the Mount Hood area, including a M 4.5 on June 29, 2002, that was located ~1 mi (~1.6 km) east of the M 3.9. Aftershocks will likely continue for hours or days, some of which may be felt.

At this time, seismologists at the Cascades Volcano Observatory and Pacific Northwest Seismic Network do not believe this swarm signifies a change in volcanic hazard at Mount Hood, but will continue to monitor the swarm and will issue further updates as the situation warrants.

45°22'26" N 121°41'42" W, Summit Elevation 11240 ft (3426 m)
Current Volcano Alert Level: NORMAL
Current Aviation Color Code: GREEN


Mount Hood Earthquake Swarm (June 5, 2021) Compared to Previous Earthquakes
Mount Hood, Oregon, earthquakes from the swarm on June 5, 2021 compared to previous earthquakes. The June 5 earthquakes are shown with red circles. Earthquakes that have occurred since 2010 are shown as unfilled circles. All circles are sized by their magnitude. Top: Map view of seismicity at Mount Hood. Black lines are roads, yellow triangles are current seismic stations. The line between A and A' is the cross section depicted in the lower graphic. Bottom: Cross-section of seismicity at Mount Hood. Symbols are the same as in the map view. The topography of Mount Hood is shown with the black line near the top of the plot.


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