惑星科学：湖の氾濫によって形作られた初期火星の河谷

On early Mars, floods from overflowing lakes may have caused around one-quarter of the erosion of ancient river valleys, according to a paper published in Nature. These findings provide fundamental insights into the formation of the Martian river valley network.

Surface water activity on ancient Mars is believed to have been responsible for eroding the planet’s river valleys and filling its lakes during a valley network-forming era that mostly ended around 3.5–3.7 billion years ago. The importance of lake flooding for the incision of large river valleys at local scales has been described. However, at a wider scale, it is often assumed that this network probably resulted from more persistent, gradual erosive processes due to the distributed water cycle on Mars.

Timothy Goudge and colleagues studied the shape and form of the Martian landscape in areas where liquid water would have once flowed through ancient river valleys. Across Mars, the findings demonstrate 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% of the volume of incised valleys on early Mars, despite the lake overflow canyons themselves only representing a small fraction (approximately 3%) of total valley length.

The authors conclude that these flooding events not only were important for valley erosion — by way of sheer volumetric contribution — but also subsequently influenced the evolution of the broader Martian landscape, notably the cratered highlands. Such events should therefore be considered when studying the properties of Martian river valleys and also when comparing how rivers interact with and influence the features of the Martian landscape against the geomorphological systems that exist on Earth.