Roughly 120 small earthquakes rumbled beneath the slopes of Mount St. Helens late last month, officials said, though the recent seismic activity does not necessarily foretell an impending eruption.

While the mountain responsible for the deadliest eruption in American history does not appear the be on the precipice of blowing its top, the recent quake swarms serve as a reminder that Mount St. Helens is still very active.

"Each of these little earthquakes is a clue and a reminder we are marching toward an eruption someday," Weston Thelen, a seismologist with U.S. Geological Survey's Cascades Volcano Observatory in Vancouver, told The Columbian, which first reported the story.

"There's nothing in this little modest seismicity, and none since 2008, that is a really good indicator of when that eruption will be," Thelen added.

Little is known about the exact origin of Mount St. Helens' magma. Recently, scientists found that the inside of the volcano was surprisingly cool and theorized that molten rock actually flowed in an underground plumbing system from east of the mountain.

Wherever the magma comes from, it constantly releases gas within the volcano, which experts believe could be the cause of the recent quakes. Most of the temblors were 1 to 2 miles beneath the surface and all of them were too weak to be felt above ground.

"We know Mount St. Helens is slowly repressurizing," Liz Westby, a Cascades Volcano Observatory geologist, told The Columbian. "We can't see it, but we think it's inflating subtly."

-- Kale Williams

kwilliams@oregonian.com

503-294-4048

@sfkale