In particular, understanding the water history of Mars requires the analysis of ancient riverbeds. The sediments deposited in the meanders also indicate that the Martian surface has experienced catastrophic flood events.
Mars is criss-crossed by many canals, remnants of a distant past where rivers and rivers flowed on its surface. At first glance, this river system appears to be relatively similar to what we know on Earth. Upon closer inspection, however, the architecture of these ancient riverbeds appears to differ significantly from that of our Earthly analogues. The manner in which the Martian canals were constructed thus provides valuable information about the dynamics of the Martian river system and its evolution over time.
Understand the hydrological behavior of a river thanks to its meander beams
Like any water-rich environment, the canals are subject to the action of water, which on the one hand erodes the rocks of the bottom and banks and on the other deposits the sediment particles carried by the current. The meanders illustrate this coupled process of erosion and sedimentation: while the outer part of the canal will be exposed to the erosive action of the flow, the inner part, where the flow is less strong, will be a place where sediments have previously been deposited and torn out .
This is how the meanders evolve over time: while one bank is being nibbled away, emphasizing the curvature of the canal, the opposite bank is under construction. In fact, the sedimentary deposits will gradually fill in the interior of the meander, forming a so-called meander rod.
Normally, these very classic sedimentary formations, found in most terrestrial rivers, grow during flood events. This growth is also visible in the structure of the meander rods in the form of lines within the deposits and a stair step structure. The study of the architecture of the meander beams thus makes it possible to determine the past hydrological behavior of the river, but also to identify specific environmental changes.
Mars channels with no earthly equivalent
However, on Mars, this type of flow deposits have also been observed in ancient tortuous channels in the region of Aeolis Dorsa. Researchers have therefore dealt with the architecture of these meander bars, using high-resolution images from the orbit of Mars (HiRISE). Their results, published in the journal Geology, show a very strong aggradation on the meander rods. These would have been built during very important events and each time would have transported enormous amounts of sediment.
This architecture is not common on Earth. Submarine channels, which serve to transport large masses of sediment (types of submarine avalanches) along continental slopes, may represent the closest analogs to what is observed on Mars. As for the channels created by terrestrial rivers, none have this extreme topography, which certainly results from very particular hydrological conditions.
The result of mega floods
For scientists, these are mega-floods that would have shaped the Martian canals. These events may have resulted from the rupture of craters filled to the brim with lakes. Such a catastrophic event, when a large volume of water suddenly spilled into the sewer network downstream of the lakes, could have happened several times. While it would take many years to create such a morphology of channels on Earth, researchers estimate that those observed on Aeolis Dorsa formed in barely a year.
Seeing it like this, dry as a plum, it’s hard to imagine that water ever flowed on the surface of Mars. And in quantity we learn today from astronomersastronomers. Massive flooding would even be the origin of the very special face we know today.
Article by Nathalie MayerNathalie Mayer, published October 3, 2021
Today Mars is a dry planet. But billions of years ago, liquid water flowed over its surface. What astronomers call crater lakes were numerous back then. Some were so large that they contained a volume of water comparable to that of a small terrestrial sea. Like the Caspian Sea for example.
And sometimes these crater lakes overflowed. Causes massive flooding. The waters then spread, digging river valleys in its wake in just a few weeks. While carrying an insane amount of sediment. Unprecedented what is happening on Earth as a result of slow erosion by the water flowing in rivers and rivers.
Mars was the scene of gigantic floods 4 billion years ago
Until then, the remains of these crater lakes had only been studied individually by researchers. Already give an idea of the magnitude of each of these floods. But today, astronomers from the University of Texas (USA) show how the 262 crater lakes that dot the surface of Mars shaped the face of the red planet.
Deep valleys hollowed out by floods
The researchers analyzed images from missions orbiting Mars to divide the red planet’s river valleys into two categories: those that are visibly connected to the rim of a crater and were therefore created by flooding, and those that appear elsewhere and on indicate a more gradual formation over time. Then the astronomers compared the depth, length and volume of these valleys. Result: The first represents almost a quarter of the volume of the Red Planet’s river valleys, while occupying only 3% of their length.
The astronomers explain that the valleys dug by the tides appear much deeper than the others: 170 meters on average for the first versus just 77 meters for the second. And although these valleys formed very quickly, they may have had a lasting impact on the surrounding landscape.
Researchers believe that river valleys formed by flooding carved out gorges so deep that it may have influenced the formation of other nearby river valleys. By lowering the local base level and thus creating depressions that favor the drainage of water in the already existing rivers. An alternative explanation for Mars’ unique topology, which scientists readily attribute to climate change.
This work underscores once again the importance of keeping in mind that the processes that occur on Earth do not necessarily occur in the same way on other planets.