Posted on 12/13/2002 8:36:39 AM PST by blam
Earth's volcanism linked to meteorite impacts
14:31 13 December 02
Exclusive from New Scientist Print Edition
Space rocks are blamed for violent eruptions (Image: GETTY)
Large meteorite impacts may not just throw up huge dust clouds but also punch right through the Earth's crust, triggering gigantic volcanic eruptions.
The idea is controversial, but evidence is mounting that the Earth's geology has largely been driven by such events. This would also explain why our planet has so few impact crater remnants.
Counting the number of asteroids we see in the sky suggests that over the past 250 million years, Earth should have been hit around 440 times by asteroids larger than one kilometre across. But scientists have found only 38 large impact craters from this period.
Dallas Abbott from Columbia University and her colleague Ann Isley from the State University of New York studied the timing of these 38 impacts and found that they correlate strongly with eruptions of "mantle-plume" volcanoes during the same period.
Deep impact
Most volcanoes come from small amounts of the Earth's upper mantle boiling over, but mantle-plume volcanoes happen when hot rock from deep within the Earth's mantle shoots straight up through the Earth's crust. The timing suggests that these volcanoes are related to asteroid impacts, Abbott and Isley report in Earth and Planetary Science Letters (vol 205, p 53).
Unreliable dates
Not everyone agrees. "I am not enthusiastic about the idea that impacts systematically control Earth's activity," says Boris Ivanov from the Institute of Geospheres Dynamics in Moscow. He has used computer models to investigate the effect of meteorites on the Earth's crust, and says he does not believe impacts are capable of having a significant effect on the planet's geological processes.
And geochemist Christian Koeberl from Vienna University argues that the dates Abbott used are not reliable. "The impacts and volcanoes can only be correlated to within tens of millions of years," he says. "This doesn't really prove anything."
But elsewhere, there is growing support for the idea that Earth's volcanism may be closely entwined with meteorite impacts.
Massive surge
Adrian Jones and David Price from University College London say Abbott's work backs up their recent computer simulations. These models suggest meteorites bigger than about 10 kilometres across could sometimes punch right through the Earth's crust, causing huge volcanic eruptions (Earth and Planetary Science Letters, vol 202, p 551).
"A large impact has the ability to cause instant melting where it hits, creating its own impact plume in the mantle and resulting in a massive surge of lava spilling out," Jones explains.
Until now Abbott and Isley were not sure how impacts might trigger volcanic eruptions, but the UCL model suggests a mechanism. It would also explain why we do not see as many meteorite craters as we might expect, as the surges of molten rock would obliterate them.
Double whammy
Jones speculates that many of the impact craters Abbott analysed could have been created by mere fragments of bigger asteroids that hit elsewhere at the same time and broke through the crust, ultimately leaving no trace.
For example, the 10 kilometre-wide asteroid that hit Chicxulub in Mexico 65 million years ago is widely blamed for wiping out the dinosaurs. But it could have been a piece from a much bigger rock that hit India, triggering the surge of volcanic activity known as the Deccan Traps.
"Many areas that exhibit extensive volcanism from the past, such as the Deccan Traps and the Siberian Traps, may in fact be sites of gigantic meteorite impacts," says Jones. Perhaps the dinosaurs would have survived a meteorite impact alone, but the double whammy of a meteorite and volcanoes pushed them to extinction.
Kate Ravilious
It's the first time I have ever heard this or even considered it. I like the simpler idea of the 'punch through.'
The shock wave radiates out in all directions from the blast at the speed of sound in rock.
You get a sharp bump straight up when the shockwave traveling the shorter path straight through the core reaches you first.
About the time that settled down the surface wave reaches you. From all sides. At once. Concentrated. Focused. Nearly as intense as the impact itself.
The pressure wave jets you and acres of liqufied bedrock towards the heavens...
Santorini could have provided all the fireworks, famines and etc. for the Exodus.
The Santinori plume would need to be 30 miles high to be visible in the Nile Valley. The recent Pinatubo volcano was 26 miles high.
The destroyed walls of Jerico are just above the Santorini ash layer and dated appropriately by charred wheat. (The Egyptian Kings List would have to be wrong)
It's just a idea, I absolutely do not want to get into another Lost Tribes discussion!!
I did some studying on Thera/Santorini/Akatori and have drifted away from it as a possibility for Atlantis, I favor South America presently. BTW, in the 1300's a Jewish guy named Joseph Nazi owned the whole island.
Do you have a Lava flag? (grin)
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