Massive floods from overflowing crater lakes were responsible for eroding at least 24% of the volume of incised valleys on early Mars, according to new research led by University of Texas at Austin planetary scientists.
Valley networks and paleolake outlet canyons on Mars: (a) distribution of analyzed valley networks (black) and paleolake outlet canyons (white); gray shading indicates the combined latitude (poleward of ±30°) and age (younger than Early Hesperian) mask used for volume calculations; (b and c) examples of the early Martian landscape dissected by both valley networks (black) and paleolake outlet canyons (white); paleolake basin extents shown by semi-transparent white polygons. Image credit: Goudge et al., doi: 10.1038/s41586-021-03860-1.
“If we think about how sediment was being moved across the landscape on ancient Mars, lake breach floods were a really important process globally,” said Dr. Tim Goudge, a researcher at the University of Texas at Austin and CIFAR.
“And this is a bit of a surprising result because they’ve been thought of as one-off anomalies for so long.”
Crater lakes were common on Mars billions of years ago when the planet had liquid water on its surface. Some craters could hold a small sea’s worth of water.
But when the water became too much to hold, it would breach the edge of the crater, causing catastrophic flooding that carved river valleys in its wake.
In 2019, Dr. Goudge and colleagues determined that these events happened rapidly.
“Remote sensing images taken by satellites orbiting Mars have allowed scientists to study the remains of breached Martian crater lakes,” he said.
“However, the crater lakes and their river valleys have mostly been studied on an individual basis. This is the first study to investigate how the 262 breached lakes across the Red Planet shaped its surface as a whole.”
The authors classified the Martian river valleys into two categories: (i) valleys that got their start at a crater’s edge, which indicates they formed during a lake breach flood; and (ii) valleys that formed elsewhere on the landscape, which suggests a more gradual formation over time.
From there, they compared the depth, length and volume of the different valley types and found that river valleys formed by crater lake breaches punch far above their weight, eroding away nearly a quarter of the planet’s river valley volume despite making up only 3% of total valley length.
“This discrepancy is accounted for by the fact that outlet canyons are significantly deeper than other valleys,” said Dr. Alexander Morgan, a researcher at the Planetary Science Institute.
At 170.5 m (559 feet), the median depth of a breach river valley is more than twice that of other river valleys created more gradually over time, which have a median depth of about 77.5 m (254 feet).
In addition, although the chasms appeared in a geologic instant, they may have had a lasting effect on the surrounding landscape.
The study suggests that the breaches scoured canyons so deep they may have influenced the formation of other nearby river valleys.
“This is a potential alternative explanation for unique Martian river valley topography that is usually attributed to climate,” the scientists said.
Their results are published in the journal Nature.
T.A. Goudge et al. 2021. The importance of lake breach floods for valley incision on early Mars. Nature 597, 645-649; doi: 10.1038/s41586-021-03860-1