Alaska's Mt. Redoubt volcano erupted in March 2009, an event preceded by a seismic "scream."
It began as series of small shuddering earthquakes beneath Alaska's Mt. Redoubt that gradually coalesced into a high-frequency "scream," according to seismologists.
While scientists could only guess as to what triggered the vibrations, there was no question about what happened next: The seismic scream was followed by 30 seconds of silence, and then a series of volcanic eruptions -- 20 over a two-week period -- that launched an enormous plume of ash resembling a mushroom cloud.
In a study published recently in Nature Geoscience, researchers examined data from the 2009 eruption and concluded that the sustained vibrations were caused by numerous so-called stick-slip movements on faults more than a mile beneath the volcano.
While researchers said it was beyond the scope of their study to determine the cause of the quake, they theorized that it was the result of pressure building in blocked magma conduits underground.
"Blockage of conduit flow increases magma pressure, driving increasingly rapid deformation until the obstruction is breached and an explosion commences," wrote lead study author Ksenia Dmitrieva, a graduate student in the department of geophysics at Stanford University, and colleagues.
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