SEATTLE - As of 1 p.m. Monday, Oregon's Mount Hood has seen about 40 earthquakes in close proximity over less than 18 hours. Such clusters of earthquakes are known as a swarm. The location of the quakes is on the southern flank of the volcano, and they are small, magnitude 2.0 or less.

Alicia Hotovec-Ellis is a volcano seismologist at the Pacific Northwest Seismic Network at the University of Washington and an expert on earthquake swarms. She says the swarms have happened in the same place before. The quakes on Mount Hood are not seen as a warning of an eruption and are probably related to water moving through rock.

Swarms of small quakes are used as a tool by scientists to monitor what's going on deep inside a volcano. Mount St. Helens has seen a series of swarms involving more than 100 key quakes over the past two months, part of a larger pattern of swarm activity dating back to the late 1990s.

Mount St. Helens last erupted in 2004.

"The style of earthquakes and where they’re locating is consistent with what we’re calling re-charge," said Seth Moran of the Cascades Volcano Observatory.

But he hastens to add that the next eruption is likely years, if not decades, away.

Reporter Glenn Farley shares more tonight on KING 5 News at 5 p.m.