Scientists studying Mars now reckon flooding from lakes contributed to around a quarter of the planet's land erosion and not just continuous flows of water that had been assumed to be the cause.
In a paper that prompts a rethink of the Red Planet's ancient landscape, researchers from The University of Texas at Austin used data from the Mars Global Surveyor (MGS), a spacecraft that was launched in 1996, to probe the assumptions that water erosion on Mars is largely down to a continuous flow in its valleys. The research sheds light on the formation of landforms created in the "valley network-forming era" of Martian history that ended between 3.5–3.7 billion years ago.
"There have been extensive efforts to understand the environmental conditions and formative mechanisms associated with valley network incision, with past global studies primarily proposing formation by surface runoff (rainfall or snowmelt), groundwater discharge at the heads of valleys, and/or subglacial drainage from large ice sheets," the paper, published in Nature this week, said.
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But analysis of existing catalogues of images and data from the Mars Orbiter Laser Altimeter on board the MGS has shown that a significant proportion of the erosion was down to "catastrophic valley formation mechanism — lake breach flooding — whereby valley incision is thought to occur rapidly from high discharge draining of water stored in lakes on the Martian surface," the paper said.
Assistant professor Timothy Goudge and colleagues argued the findings show that the overflowing of water stored in lakes had a crucial role in the formation of the planet's ancient river valley network. Indeed, these overflow floods were found to be responsible for the rapid erosion of at least 24 per cent of the valleys cut into the early Martian surface, despite the fact that lake overflow canyons themselves only make up 3 per cent of total valley length.
The researchers say the results should influence the study of the broader landscape of Mars, and when comparing how rivers interact with and influence the features of the Martian landscape against the changes in geology on Earth.
"We conclude that lake breach floods were a major geomorphic process responsible for valley incision on early Mars, which in turn influenced the topographic form of many Martian valley systems and the broader landscape evolution of the cratered highlands. Our results indicate that the importance of lake breach foods should be considered when reconstructing the formative conditions for Martian valley systems," the authors said. ®