From studying rock formations from satellite images, planetary researchers know that hundreds of craters across the Martian surface were once filled with water. More than 200 of these paleolakes have outlet canyons tens to hundreds of miles long and several miles wide carved by water flowing from the lakes. A research team from the University of Texas at Austin and NASA’s Marshall Space Flight Center has found evidence that sometimes the paleolakes would take on so much water that they overflowed and burst from the sides of their basins, creating catastrophic floods that carved canyons very rapidly, perhaps in a matter of weeks.
Jezero Crater, one of the paleolakes examined in the study, is a paleolake and potential landing site for NASA’s Mars 2020 rover mission to look for past life; the outlet canyon carved by overflow flooding is visible in the upper right side of the crater; ancient rivers carved the inlets on the left side of the crater. Image credit: NASA / Tim Goudge.
“These breached lakes are fairly common and some of them are quite large, some as large as the Caspian Sea,” said lead author Dr. Tim Goudge, a postdoctoral researcher in the Jackson School of Geosciences at the University of Texas at Austin.
“So we think this style of catastrophic overflow flooding and rapid incision of outlet canyons was probably quite important on early Mars’ surface.”
Using high-resolution images taken by NASA’s Mars Reconnaissance Orbiter, Dr. Goudge and co-authors examined the topography of the outlets and the crater rims and found a correlation between the size of the outlet and the volume of water expected to be released during a large flooding event.
“If the outlet had instead been gradually whittled away over time, the relationship between water volume and outlet size likely wouldn’t hold,” Dr. Goudge said.
In total, the researchers examined 24 paleolakes and their outlet canyons across Mars.
While massive floods flowing from Martian craters might sound like a scene in a science fiction novel, a similar process occurs on Earth when lakes dammed by glaciers break through their icy barriers.
The team found that the similarity is more than superficial. As long as gravity is accounted for, floods create outlets with similar shapes whether on Earth or Mars.
“This tells us that things that are different between the planets are not as important as the basic physics of the overflow process and the size of the basin,” Dr. Goudge explained.
“You can learn more about this process by comparing different planets as opposed to just thinking about what’s occurring on Earth or what’s occurring on Mars.”
Although massive floods on Mars and Earth are governed by the same mechanics, they fit into different geological paradigms.
On Earth, the slow-and-steady motion of tectonic plates dramatically changes the planet’s surface over millions of years.
In contrast, the lack of plate tectonics on Mars means that cataclysmic events — like floods and asteroid impacts — quickly create changes that can amount to near permanent changes in the landscape.
“The landscape on Earth doesn’t preserve large lakes for a very long time. But on Mars these canyons have been there for 3.7 billion years, a very long time, and it gives us insight into what the deep time surface water was like on Mars,” said co-author Dr. Caleb Fassett, a researcher at NASA’s Marshall Space Flight Center.
The study was published in the journal Geology.
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Timothy A. Goudge et al. Incision of paleolake outlet canyons on Mars from overflow flooding. Geology, published online November 16, 2018; doi: 10.1130/G45397.1
