Alaska's Redoubt Volcano March 2009 eruption analysis shows tremors reached high "scream" frequencies before abruptly stopping at five eruptions, according to a University of Washington (UW) news release.
"The frequency of this tremor is unusually high for a volcano, and it's not easily explained by many of the accepted theories," Alicia Hotovec-Ellis, a University of Washington doctoral student in Earth and space sciences, said in the release.
Hotovec-Ellis is the lead author of the paper published in the Journal of Volcanology and Geothermal Research that describes the research.
According to UW's release, researchers say documenting the volcano's pressurization right before an explosion may help refine models and "allow scientists to better understand what happens during eruptive cycles in volcanoes like Redoubt."
Researchers have not pinpointed the source of the earthquakes and harmonic tremor.
"[However],scientists at the USGS Alaska Volcano Observatory have dubbed the highest-frequency harmonic tremor at Redoubt Volcano 'the screams' because they reach such high pitch compared with a 1-to-5 hertz starting point," UW said.
Volcanoes will sometimes release sound when magma, a mixture of molten rock, suspended solids and gas bubbles, resonates as it pushes up through Earth's crust, according to UW.
"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," UW said. "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."
Small earthquakes are produced from each sudden movment. With the increase of pressure build-up tremors become smaller and rapid, and the occurrence blends into a continuous harmonic quake.
"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."
To read more about Hotovec-Ellis and her team's finding about the volcanic screams, click here.
