Lava and Water Battled at Grand Canyon

Feb. 12, 2008 -- 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 which dammed the river and then burst.

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

Among the conclusions: Over that time there have been no less than four lava flows that dammed the river in the western Grand Canyon. Some of these dams were breached by dramatic floods and others may have been simply eroded away as the river flowed over their tops.

What's more, there have been many more lava floods into the canyon which did not necessarily dam the river. The trick for geologists has been sorting all the lava flows out, since the terrain is particularly hard to work in.

"The area is extremely rugged and the relief extreme," said 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 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," said Crow. There have even been small cinder cone volcanoes erupting right inside the canyon, he said.