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By Blair Shiff
May 18, 2017, 5:06 AM ET
Mount St. Helens erupted on May 18, 1980, after two months of increasing volcanic activity.
Since its most recent eruption in 2008, there has been a swarm of earthquakes, which are thought to be a result of the magmatic system's "recharging," according to the Pacific Northwest Seismic Network.
Similar seismic swarms were detected during recharging periods before a small eruption in 2004 and through a period of volcanic activity that ended in 2008.
In March through May of this year, swarms of deep earthquakes, not even felt on the surface, have been detected.
Seismic swarms do not directly indicate that an eruption is imminent, because volcanic forecasting is difficult, according to the U.S. Geological Survey.
Over the nearly four decades since the cataclysmic eruption, the USGS has noticed signs of recovery near Mount St. Helens.
These signs of regrowth are positive, but there are also signs of increased seismic activity under the mountain.