Ancient Flash Floods Sculpted Earth, Mars

A megaflood seems to have scoured a canyon on Earth which, interestingly, looks a lot like canyons on Mars. And that new conclusion, researchers say, could help figure out whether there was ever life on Mars.

To better understand how massive canyons possibly formed on Mars, scientists investigated Idaho's Box Canyon, which like many Martian gorges, was sculpted by water in volcanic rock. This deep valley ends with a round, steep wall, giving it an "amphitheater shape," and was long considered a classic example of how a canyon formed through gradual erosion, as groundwater seeped through the canyon walls and wore the hard rock away.

But now it seems a massive flash flood may actually have carved out Box Canyon roughly 45,000 years ago. By implication, many canyons on Mars that are cut in volcanic rock and amphitheater-shaped like Box Canyon might have formed the same way, the researchers said.

Plunge pools

The scientists analyzed geological features of Box Canyon, such as depressions or "plunge pools" that appear to have been the site of ancient waterfalls, and the age of large boulders found downstream.

"We fully expected to find Box Canyon was carved by groundwater, but then all the evidence we found pointed at a megaflood," said Michael Lamb, a geomorphologist at the University of California, Berkeley.

Lamb and his colleagues found scour marks from flooding at the head of the canyon, and discovered that all the rock that was moved to form the gorge required a vast amount of water to propel it the distance it went.

They conclude Box Canyon was formed during a catastrophic flood or series of floods, presumably caused by melting ice sheets that lay at mountains to the north.

"The entire canyon seems to have been cut out of the earth by this flood," Lamb said. Although hardened lava, or basalt, is hard, "it's very fractured material. When lava cools, it contracts and cracks just like mud does. All this cracking makes the basalt like a pile of stacked blocks. So while small floods might cause little erosion, a large enough flood can pull these blocks out of place."

And the megaflood was likely very powerful indeed. "Imagine forcing a quarter of the flow in the Mississippi through a chute 32 times as narrow and 1,000 times as steep as the Mississippi River channel," Lamb told SPACE.com.

Huge boulders moved

Conservative estimates suggest the megaflood blasted 800 to 2,800 metric tons of water per second, reaching speeds of up to some 22 mph within the canyon. This explains how boulders the scientists examined could have dropped on the ground seemingly out of nowhere ? the flood picked them up and hurled them along. All in all, the canyon could have been carved in as little as 35 to 160 days.

The canyons of Mars may have been carved the same way ? from megafloods of water and not, say, liquid carbon dioxide, which also once flowed over the surface of the red planet. Carbon dioxide is the stuff that puts fizz in soda.

"Carbon dioxide tends to erupt, be really explosive, and shoot into the air, and not form bottom-hugging flows," Lamb said. "The valleys on Mars are hundreds of kilometers long, eroded into rock, and probably required a denser fluid like water."

If one can tell how water flowed on Mars, "that has implications on us living on Mars and on finding out whether there was other life on Mars," Lamb added.

But studying Martian canyons for signs of formation by flooding will be very hard.

"The clues of the flood event were relatively subtle at Box Canyon. It wasn't until our second field season that we saw the scour marks at the head of the canyon," Lamb said. "Even the highest resolution imagery from Mars, which is about three-quarters of a meter per pixel, would not reveal those marks. And Box Canyon formed only 45,000 years ago, while some of the canyons on Mars may have formed 3.5 billion years ago, about 100,000 times older, and they may have altered much since then. This makes studying Earth analogues all the more important for understanding Mars."

The findings are detailed in the May 23 issue of the journal Science.

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