What does a volcano say just before blowing its top? Well, like some people, it says ahhhhhhhhhhhhhhhhhhhhh!!!!!!
That’s what University of Washington scientist Alicia Hotovec-Ellis, a doctorial student in Earth and space sciences, discovered when exploring pre-eruption activities in Alaska’s Redoubt Volcano.
Sometimes volcano gets rhythm:
A new analysis of an eruption sequence at the Redoubt Volcano in March 2009 shows that the harmonic tremor glided to substantially higher frequencies and then stopped abruptly just before six of the eruptions, five of them coming in succession.
“The frequency of this tremor is unusually high for a volcano, and it’s not easily explained by many of the accepted theories,” said Hotovec-Ellis.
Here’s the gist of the UW story:
Documenting the activity gives clues to a volcano’s pressurization right before an explosion. That could help refine models and allow scientists to better understand what happens during eruptive cycles in volcanoes like Redoubt, she said.
The source of the earthquakes and harmonic tremor isn’t known precisely. Some volcanoes emit sound when magma – a mixture of molten rock, suspended solids and gas bubbles – resonates as it pushes up through thin cracks in the Earth’s crust.
But Hotovec-Ellis believes in this case the earthquakes and harmonic tremor happen as magma is forced through a narrow conduit under great pressure into the heart of the mountain. The thick magma sticks to the rock surface inside the conduit until the pressure is enough to move it higher, where it sticks until the pressure moves it again.
Each of these sudden movements results in a small earthquake, ranging in magnitude from about 0.5 to 1.5, she said. As the pressure builds, the quakes get smaller and happen in such rapid succession that they blend into a continuous harmonic tremor.
“Because there’s less time between each earthquake, there’s not enough time to build up enough pressure for a bigger one,” Hotovec-Ellis said. “After the frequency glides up to a ridiculously high frequency, it pauses and then it explodes.”