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Lava left its mark on Grand Canyon

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Abedabun
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« on: February 17, 2008, 11:23:32 pm »

Lava left its mark on Grand Canyon
Friday, 15 February 2008 Larry O'Hanlon

Discovery News


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The Grand Canyon was not just carved by water. It has also been the scene of periodic wars between the Colorado River and volcanic eruptions that dammed the river, then burst.

New airborne elevation survey data and radioisotope dating of Grand Canyon lava flows sheds new light on the battle between water and molten rocks there over the past 725,000 years.

Over that time there have been no fewer than four lava flows that dammed the river in the western Grand Canyon.

Dramatic floods breached some of these dams and other dams may have been simply eroded away as the river flowed over their tops.

There have also been many more lava floods into the canyon that did not necessarily dam the river.

The trick for geologists has been sorting out all the lava flows, since the terrain is particularly hard to work in.

"The area is extremely rugged and the relief extreme," says Ryan Crow, a planetary scientist at the University of New Mexico and lead author of a paper on the new data in the February issue of the journal Geosphere.

"It's extremely difficult to get around."

The same rugged canyon country and eons of erosion have dismembered the lava flows, making them very difficult to reconstruct.

"Maybe hundreds of [lava] flows have cascaded into the canyon," says Crow.

There have even been small cinder cone volcanoes erupting right inside the canyon, he says.

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Abedabun
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« Reply #1 on: February 17, 2008, 11:24:46 pm »



Volcanic lava flows onced dammed the river that ran through the Grand Canyon (Source: iStockphoto)
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Abedabun
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« Reply #2 on: February 17, 2008, 11:39:47 pm »

Collecting data
To sort out all the lava flows, Crow and his colleagues used light detection and ranging (LIDAR) data that was originally collected for the Grand Canyon Monitoring and Research Center in the northern hemisphere spring of 2000.

The LIDAR survey data allowed the team to map out the lava flows in relation to sea level, making it easier to identify the tops and bottoms of the lava flows seen pasted on the walls of the canyons.

As for exactly how the lava dams worked, how far they backed up water and how violently they failed, that's all still largely a matter of conjecture.

"There are many possible scenarios and explanations for how the dams were formed or were destroyed, and it's likely that we'll never know them all," says Dr Cassandra Fenton, a geochemist at GeoForschungsZentrum Potsdam in Germany.

Fenton has studied what may be some of the largest lava dams in the Grand Canyon and their outburst floods.

"It makes you wish you could have been standing on the rim of the Grand Canyon watching it all happen when those lavas were damming the river, or see when the river finally overtook the dams," she says

http://www.abc.net.au/science/articles/2008/02/15/2164047.htm?site=science&topic=latest
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