Home Emergency Management News Another PNW Earthquake Swarm, This Time Under Oregon's Mount Hood

Another PNW Earthquake Swarm, This Time Under Oregon's Mount Hood


Mount Hood is the latest Cascade peak to experience a swarm

Pacific Northwest volcanoes have been making many headlines recently, and now Oregon's Mount Hood is getting in on the fun.

First, the United States Geological Survey (USGS) reported an earthquake swarm under Mount St. Helens in southern Washington, and then it was the 36-year anniversary of Mount St. Helens eruption. Now, the USGS is reporting another earthquake swarm, this time under Mount Hood.

The USGS detected a swarm of small earthquakes under Mount Hood on May 15 and 16, 2016. The swarm peaked near 6 a.m. on May 16, when the region was experiencing up to 20 small quakes per hour. None of the earthquakes in the swarm exceeded 1.8-magnitude, and the quakes were all located approximately 2 to 3 miles south of the summit at depths of about 2 to 3 miles below sea level.

For the sake of comparison, the swarm under Mount St. Helens that ended on May 5 has quakes that ranged from about magnitude-0.5 to magnitude-1.3 at depths of about 1.2 to 4 miles.

High threat potential

The USGS' Cascades Volcano Observatory (CVO) lists nine total regions in Washington and Oregon on their list of peaks that have high to very high threat potential of significant volcanic activity. There are also 28 regions in Alaska and eight in California that the USGS considers to have high threat potential.

In Oregon, there are four areas on the "high threat" list, and Mount Hood, the tallest peak in the state at 11,250 feet, is one of them. Crater Lake, Newberry, and Three Sisters are the other three listed as "highest priority" in Oregon.

Mount Hood in Oregon
Mount Hood in Oregon

Mt. Hood swarms are common occurrences

According to the USGS, the recent swarm under Mount Hood is typical for the region. The area surounding the peak usually experiences up to two swarms per year. Some swarms last just a couple of days, but they can last up to a few weeks. One of the most noteworthy swarms near Mt. Hood in recent history occurred during the months of June and July in 2002, as the quakes reached as high as magnitude 4.5 and some tremors were felt by a large number of people.

Scientists consider the recent swarm of small quakes "tectonic" in nature, as opposed to quakes that are directly linked to magmatic processes. That is, the small tremors occurred on pre-existing regional faults and represent relatively little threat to the region.

Matt Mills Matt Mills has been involved in various aspects of online media, both on the editorial side and on the technology side, for more than 16 years. He holds a Master's Degree in Journalism from Northwestern University's Medill School of Journalism, and is currently involved in multiple projects focused on innovation journalism.