Fast and Furious Floods From Overflowing Craters Shaped the Surface of Mars

Mars Outlet Crater

A colored topographical image showing river valleys on Mars. The outlet canyon Loire Vallis (white line) formed from the overflow of a lake in Parana Basin (outlined in white). Black lines indicate other river valleys formed by processes other than lake overflows. Background is colored Mars Orbiter Laser Altimeter-derived topography over a Thermal Emission Imaging System image mosaic. Image is approximately 650 kilometers across. Credit: NASA/GSFC/ JPL ASU

On Earth, river erosion is usually a slow-going process. But on Mars, massive floods from overflowing crater lakes had an outsized role in shaping the Martian surface, carving deep chasms and moving vast amounts of sediment, according to a new study led by researchers at The University of Texas at Austin.

The study, published today (September 29, 2021) in Nature, found that the floods, which probably lasted mere weeks, eroded more than enough sediment to completely fill Lake Superior and Lake Ontario.

“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 lead author Tim Goudge, an assistant professor at the UT Jackson School of Geosciences. “And this is a bit of a surprising result because they’ve been thought of as one-off anomalies for so long.”

Goudge Breached Mars Lake

The remains of a former crater lake on Mars surrounded by other smaller craters. The large outlet canyon in the upper left formed during a crater breach event. Credit: Goudge et al.

Crater lakes were common on Mars billions of years ago when the Red 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. A 2019 study led by Goudge 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. However, the crater lakes and their river valleys have mostly been studied on an individual basis, Goudge said. This is the first study to investigate how the 262 breached lakes across the Red Planet shaped the Martian surface as a whole.

The research entailed reviewing a preexisting catalog of river valleys on Mars and classifying the valleys into two categories: valleys that got their start at a crater’s edge, which indicates they formed during a lake breach flood, and valleys that formed elsewhere on the landscape, which suggests a more gradual formation over time.

Global Map of Mars River Valleys

A global map of Mars showing river valleys around the Red Planet. River valleys formed by crater lake breaches are in white. River valleys that formed gradually over time are in black. Credit: Goudge et al.

From there, the scientists 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 Red 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 study co-author Alexander Morgan, a research scientist at the Planetary Science Institute.

At 559 feet (170.5 meters), 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 254 feet (77.5 meters).

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. The authors said this is a potential alternative explanation for unique Martian river valley topography that is usually attributed to climate.

The study demonstrates that lake breach river valleys played an important role in shaping the Martian surface, but Goudge said it’s also a lesson in expectations. The Earth’s geology has wiped away most craters and makes river erosion a slow and steady process in most cases. But that doesn’t mean it will work that way on other worlds.

“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.”

Reference: “The importance of lake breach floods for valley incision on early Mars” by Timothy A. Goudge, Alexander M. Morgan, Gaia Stucky de Quay and Caleb I. Fassett, 29 September 2021, Nature.
DOI: 10.1038/s41586-021-03860-1

The study’s other co-authors are Jackson School postdoctoral researcher Gaia Stucky de Quay and Caleb Fassett, a planetary scientist at the NASA Marshall Space Flight Center.

NASA funded the research.

2 Comments on "Fast and Furious Floods From Overflowing Craters Shaped the Surface of Mars"

  1. All of those other many distributaries take time to develop by erosion implying persistent up-stream sources. That could not have happened in “mere weeks”. In addition, those craters if filled with water would have some water left after draining into the river. This water would have evaporated leaving behind mineral evaporites that should provide evidence of the composition of the Martian oceans. On Earth those would mostly be chlorides of sodium (halite) and calcium sulfates. So far, there have been no significant chlorides yet found. That has implications for life as well.

    • Torbjörn Larsson | September 30, 2021 at 11:38 pm | Reply

      There are lots of sediment minerals that are mostly missing, like carbonates.

      On modern Mars you find chloride in apatite [“THE VOLATILE CHEMISTRY OF APATITE IN PLANETARY MATERIALS: IMPLICATIONS FOR THE BEHAVIOR OF VOLATILES DURING PLANETARY DIFFERENTIATION?”, McCubbin et al., LPSC 2013]

      “Apatites from martian basalts are anomalous in that compositions cover a wide range and are more Cl-rich than apatites from basalts on Earth, Moon, or 4-Vesta (Fig. 1). Some martian apatite compositions overlap with Cl-rich compositions from ordinary chondrites. However, this observation alone does not necessarily imply anything about Mars’ differentiation history. There are a number of scenarios that could cause a global-scale difference between apatite compositions among planetary basalts.

      One possibility is that Mars has a ubiquitous Cl-rich phase in its mantle that formed during magma ocean crystallization. In fact, [25] recently speculated that scapolite may be present within the martian mantle, as long as the bulk Cl content of Mars was sufficiently elevated.

      Another possibility is that all martian basalts that have been analyzed to date have been substantially modified or contaminated by Cl-rich fluids. Metasomatized terrestrial settings are a common host for Cl-rich apatites [8, 14], and this process has already been shown to have operated on Mars through studies of the chassignites, nakhlites, and ordinary chondrites [15, 17, 26-27]. However, contamination by Cl-rich fluids may be difficult to justify given that all the martian basalts have Cl-rich apatite, but the basalts have preserved their properties of geochemical enrichment/depletion and variability in fO2 [28-29].

      A third possible explanation for martian apatite compositions is that Mars could be highly depleted in fluorine, although a process for such a depletion is presently unknown. A final possible explanation for the chlorine-rich apatite compositions in martian basalts is that there was no magma ocean on Mars, and the Cl from chondritic precursor materials remained sequestered in the mantle. This model has several problems, the largest of which include the rapid time constraints for core formation on Mars and the antiquity of the geochemically enriched and depleted silicate reservoirs based on isotopic studies [30-31].

      Regardless, Mars is a clear outlier when relative volatile abundances of basaltic apatite are compared with Earth, Moon, and 4-Vesta, and it is going to take more work to determine the reason(s) behind the differences.”

      Another large chloride reservoir is in the soil, where diverse perchlorates are 0.5 % by mass. The modern martian soil is windblown and may constitute 1 km of the upper crust, suggesting it is analogous in reservoir function and chlorine content to Earth’s modern oceans.

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