[meteorite-list] Earth's Volcanism Linked To Meteorite Impacts

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Thu Apr 22 09:53:34 2004
Message-ID: <200212121728.JAA23486_at_zagami.jpl.nasa.gov>

http://www.newscientist.com/news/news.jsp?id=ns99993171

Earth's volcanism linked to meteorite impacts
New Scientist
December 11, 2002
 
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.

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.
Received on Thu 12 Dec 2002 12:28:30 PM PST