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.
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.