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.

"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.