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

Right into enemy hands? ISIS shows off new weapons allegedly airdropped by US (VIDEO)
2014 10 23
Islamic State has published a new video in which a jihadist shows off brand-new American hardware, which was purportedly intended for the Kurds they are fighting in the Syrian border town of Kobani. The undated video, posted by the unofficial IS mouthpiece “a3maq news”, sees a jihadist showing several boxes of munitions with English-language markings, with a parachute spread out on ...
STAGED INFECTION: Has The Ebola ‘Outbreak’ Narrative Fallen Apart?
2014 10 22
Over the past month, the ‘pandemic’ propaganda surrounding the deadly Ebola virus seemed to reach vitriolic levels – raising serious questions about the validity of this current viral outbreak… On Monday of this week, it was reported that 48 people were released and cleared after a 21-day quarantine due to their contact with the now deceased Ebola-stricken patient Thomas Eric ...
6,000-Year-Old Temple with Possible Sacrificial Altars Discovered
2014 10 21
A 6,000-year-old temple holding humanlike figurines and sacrificed animal remains has been discovered within a massive prehistoric settlement in Ukraine. Built before writing was invented, the temple is about 60 by 20 meters (197 by 66 feet) in size. It was a "two-story building made of wood and clay surrounded by a galleried courtyard," the upper floor divided into five ...
What happened to Journalist Serena Shim? Assassinated? Find out what happened to Serena, Press TV director calls on Turkey
2014 10 21
Press TV news director Hamid Reza Emadi says the “suspicious death,” of the news channel’s correspondent in Turkey is a tragedy for “anyone who wants to get the truth.” Emadi made the remarks in an interview with Press TV on Sunday following Serena Shim’s death across the border from Syria’s Kurdish city of Kobani, where the ISIL terrorists and Kurdish fighters ...
Ancient Roman Nanotechnology Inspires Next-Generation Holograms for Information Storage
2014 10 21
The Lycurgus Cup, as it is known due to its depiction of a scene involving King Lycurgus of Thrace, is a 1,600-year-old jade green Roman chalice that changes colour depending on the direction of the light upon it. It baffled scientists ever since the glass chalice was acquired by the British Museum in the 1950s, as they could not work ...
More News »