Volcanic earthquakes produce a “seismic scream” just before eruption
2013 07 22

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

Whistleblower: Margaret Thatcher knew all about underage sex ring
2014 07 29
Margaret Thatcher was told about alleged sex parties with under-age boys held by one of her closest aides claims her former personal bodyguard. Barry Strevens, who worked as the prime minister’s personal bodyguard, said that he passed on allegations about her confidant Sir Peter Morrison. The former senior police officer said that Lady Thatcher appointed Sir Peter deputy party chairman of the ...
The Absurd, Bureaucratic Hell That Is the American Police State
2014 07 29
“The greatest evil is not now done in those sordid ‘dens of crime’ that Dickens loved to paint. It is not done even in concentration camps and labour camps. In those we see its final result. But it is conceived and ordered (moved, seconded, carried, and minuted) in clean, carpeted, warmed and well-lighted offices, by quiet ...
Australian Government Pushing ‘Internet Tax’ To Pay For NSA Style Spying
2014 07 29
Forcing private companies to become mass surveillance hubs The Australian government is pushing to implement a ”surveillance tax” on the people of the country in order to pay for a mandate that would see communications companies retaining data on customers for two years. In a disturbing development that should serve as a warning to Americans, the Australian Attorney-General admitted that the surveillance ...
Japanese leader proposes first-ever ’Robot Olympics’
2014 07 29
Nations of the world will be sending their most talented athletes to Tokyo in 2020 for the Olympic Games – but if Japanese Prime Minister Shinzo Abe gets his way, they might also be pitting robots against each other. Abe announced his vision while touring robotics factories in Tokyo and Saitama, which is located just north of the country’s capital. According ...
Israel Student Union Set Up “War Room” to Sell Gaza Massacre on Facebook
2014 07 29
This article was published on July 14, 2014. The death toll in Gaza as of today, July 23, 2014, reaches 678 according to Al-Akhbar. Students at the IDC Herzliya “war room,” seen here in a screenshot, focus on posting propaganda justifying Israel’s attack on Gaza on Facebook. As the death toll from Israel’s savage bombardment of Gaza continues to climb, Israel has ...
More News »