The stunning river valleys we find on Earth have been shaped by long periods of erosion, sometimes up to millions of years. On Mars, it seems, things can happen a lot faster. About a quarter of the erosion of all river valleys appear to be caused by flooding from overflowing lakes.
Reporting in Nature, researchers have shown that lake breach floods were a major player in shaping the surface of the Red Planet. These events were able to erode enough sediments in a matter of weeks to fill Lake Superior and Lake Ontario. Lake Superior is the third biggest in the world for volume.
When Mars was wet over 3.5 billion years ago, many of the planet's large craters could hold an ocean worth of water. Water breaching the rim of such a crater was a catastrophic event that could change the surrounding landscape. The new paper looks at 262 breached lakes that had such an impact on the Martian surface.
“If we think about how sediment was being moved across the landscape on ancient Mars, lake breach floods were a really important process globally,” lead author Tim Goudge, an assistant professor at the UT Jackson School of Geosciences, said in a statement. “And this is a bit of a surprising result because they’ve been thought of as one-off anomalies for so long.”
The researchers suggest that the river valleys of Mars need to be divided into two categories: valleys that started near a crater and valleys located elsewhere. The former make up only 3 percent of all the valleys in length. But they appear to be responsible for 24 percent of the volume of river valleys on the Red Planet.
“This discrepancy is accounted for by the fact that outlet canyons are significantly deeper than other?valleys,” said study co-author Alexander Morgan, a research scientist at the Planetary Science Institute.
The median depth for river valleys from breached craters is 170.5 meters (559 feet). That’s over twice as deep as the slow-carved river valleys that sport a median depth of 77.5 meters (254 feet). It shows just how different Mars was from Earth, where the actions of the elements and the biosphere have slowly erased the presence of craters. The same has not happened on Mars.
“When you fill [the craters] with water, it’s a lot of stored energy there to be released,” Goudge said. “It makes sense that Mars might tip, in this case, toward being shaped by catastrophism more than the Earth.”