Magma stores are recharging inside Mount St. Helens, setting off a swarm of small earthquakes since last month, according to the U.S. Geological Survey.
Since the catastrophic eruption of May 18, 1980, scientists have been conducting research and collecting data on the volcano to learn more about its typical behavior.
Since March 14, a number of small earthquakes have occurred beneath the volcano at a depth between 1.2 to 4 miles. The earthquakes have low magnitudes of 0.5 or less, with the largest a 1.3.
Over the last eight weeks, there have been more than 130 earthquakes located by the Pacific Northwest Seismic Network and many more that are too small to be detected.
The USGS says the earthquake rates have been steadily increasing since March, reaching nearly 40 located earthquakes per week, but there are no signs of an imminent eruption.
The quakes are too small to be felt, even if you were standing on the surface directly above.
"The earthquakes are volcano-tectonic in nature, indicative of a slip on a small fault," according to the USGS. "Such events are commonly seen in active hydrothermal and magmatic systems. The magma chamber is likely imparting its own stresses on the crust around and above it, as the system slowly recharges. The stress drives fluids through cracks, producing the small quakes. The current pattern of seismicity is similar to swarms seen at Mount St. Helens in 2013 and 2014; recharge swarms in the 1990s had much higher earthquake rates and energy release."
No anomalous gases, increases in ground inflation or shallow seismicity have been detected with the swarm, and there are no signs of an imminent eruption.
As was seen at Mount St. Helens between 1987 and 2004, recharge can continue for many years beneath a volcano without an eruption.
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