July 15, 2013. Redoubt Volcano in Alaska before the eruption has issued an unusually high-pitched sound that arose due to fluctuations in the Earth's crust in a series of small earthquakes preceding the eruption, according to a paper published in the journal
Volcanic eruption is often preceded by the slack of the earthquake. They can go after each other with such a small gap, that the earth's crust, fluctuating, low-frequency issues "trill." Scientists led by a graduate of the Moscow State University of Geodesy and Cartography Ksenia Dmitrieva from Stanford University (USA) analyzed the eruption of Redoubt volcano in 2009. They found that "trill," which he gave off, reached an unusually high frequency. It started with 1 hertz and has reached almost 30 hertz — the frequency at which the sound can already hear the people.
"Rate this" trills "unusually high for the volcano, it is difficult to explain by conventional theories," — said study co-author Alicia Gotovek-Ellis (Alicia Hotovec-Ellis) from the University of Washington (USA).
It is believed that some volcanoes emit a sound, because the crust resonates when magma breaks through narrow cracks in it.
Dmitrieva and her colleagues believe that in the case of Redoubt other reason. During the eruption of the volcano magma chamber of a volcano rising from the surface through a narrow channel, occasionally getting stuck on the road, until the bottom of accumulating enough pressure to push it further. Each time the magma moved up, there was a small earthquake of magnitude 0.5-1.5. As soon as the pressure at the bottom grew, earthquakes became weaker and more, up to 30 per second. For half a minute before the eruption pressure peaked edges of tectonic fault movement under the volcano became smoother and "trill" broken.
Sounds such as volcanic eruptions accompanied Arenal in Costa Rica, and Soufriere Hills in the Caribbean.