Volcanic earthquakes produce a “seismic scream” just before eruption
2013-07-22 0:00

By John Timmer | Ars Technica



Volcanic activity is intimately associated with seismic activity. You simply can’t force molten or semi-molten rock through a mountain without cracking a few faults in the process. If we were ever able to understand how to read the seismic activity correctly, it could provide valuable advanced warning about impending eruptions.

A 2009 eruption of Alaska’s Redoubt Volcano may not get us much closer to an advanced warning, but it provides a detailed glimpse of the last moments before an explosive eruption. Shortly before the eruption, small faults within the volcano were breaking so frequently that they merged into what’s being called a "seismic scream." Then, within a few minutes of the eruption, the scream got cut off as the last resistance gave way.

Redoubt is a stratovolcano, built from material that melted as the Pacific plate subducted beneath Alaska. Like some more famous examples, such as Mount St. Helens, it alternates between slow eruptions of extremely viscous rock and sudden, explosive ones. The 2009 eruption was accompanied by a number of small explosions (small at least in the sense that the mountain was still there afterward); the researchers focused on the seismic activity that led up to these explosions.

Most of the earthquakes associated with the eruption were small (between magnitude 0.5 and 1.5) and centered a few kilometers below the volcanic vent. There was plenty of activity of this sort seen during the eruption, but something unusual happened before the largest explosion: "These small earthquakes occurred in such rapid succession—up to 30 events per second—that distinct seismic wave arrivals blurred into continuous, high-frequency tremor." This continuous tremor is what is being called the "seismic scream."

The earthquakes themselves might be enough to make you nervous, but something even more unnerving happened after a few minutes of screaming: things suddenly went quiet. For somewhere between 30 seconds to a minute, the low magnitude quakes stopped, although sometimes larger ones would happen. And then, the explosion hit.

[...]

Read the full article at: arstechnica.com




Related Articles
Spectacular Volcanic Plugs & Natural Monoliths
Scientist argues that volcanoes, not meteorite, killed dinosaurs
Scientists locate ’trigger’ for large-scale volcanic eruptions
What if Yellowstone’s supervolcano erupts?


Latest News from our Front Page

Gunman Storms Dutch TV Station Demanding Airtime
2015-01-30 23:32
Dutch authorities have released few details about the bizarre case of 19-year-old Tarik Zahzah’s attack on the main news studio of television station NOS on Thursday. To get the obvious question out of the way first, the police say there is no evidence that Zahzah, who is half-Egyptian, acted on behalf of organized terrorism. The authorities always say that on the ...
How Alan Dershowitz bullied rape victims to protect a serial child molester
2015-01-30 23:40
Harvard law professor Alan Dershowitz always felt children were fair game for Israeli missiles. Now the question is whether he thinks they are fair game for the sexual exploits of his powerful associates and himself. Dershowitz and the UK’s Prince Andrew were accused in a recent court filing of raping a teenage girl who was forced into sexual slavery by ...
Alchemical Banksters
2015-01-30 22:39
This past week, the world's preeminent vultures, the economic power elite, met in Davos to discuss the maintenance of their global fiat hegemony. Highlights included furthering austerity, noting that the serf class can't have air conditioning and cars, as well as cheering on the death of privacy through the rise of technocracy. The degenerate elite, completely out of touch with ...
Men must prove a woman said ’Yes’ under tough new rape rules
2015-01-30 4:54
New guidance will be issued to all police forces and prosecutors as part of a ’toolkit’ to move rape investigations into the 21st century Men accused of date rape will need to convince police that a woman consented to sex as part of a major change in the way sex offences are investigated. The Director of Public Prosecutions said it was ...
4 beheaded in Saudi Arabia less than a week into King Salman's rule
2015-01-30 3:13
Comment: So when will the the "Human rights" promoting liberal west elite decide invade Saudi Arabia like they did Libya? Members of Magic Movement stage a mock execution scene in protest of Saudi Arabia beheading of eight Bangladeshi workers in October 2011. Four people have been executed in Saudi Arabia less than a week after 79-year-old King Salman assumed power following the ...
More News »