PORTLAND, Ore. (KOIN) — Nearly 100 small earthquakes were recorded under Mount Hood throughout Sunday and for much of the day Monday.
The tremblors first hit around 6 p.m. Sunday and continued into Monday afternoon. None of them measured at or above 3.0, so people couldn’t feel them.
The largest quake in the swarm originally measured at 2.4, according to the USGS, but was later downgraded to a 1.9. It happened around 6:40 a.m. Monday.
Other quakes recorded under the mountain were smaller and shallower. The tremblors occurred 1-4 miles below the area around Government Camp.
Geologist Scott Burns with Portland State University says the series of small earthquakes indicates some movement beneath the surface of the old volcano.
“You have a whole bunch together, it’s called a swarm,” Burns explained. “Anytime you have a swarm under an active volcano, it’s a sign that magma is moving up.”
But the USGS says swarms like this are fairly common on Mount Hood, happening once or twice a year. This one occurred near a vent where swarms are normal.
Mount Hood hasn’t erupted since the 1700s.