Research press release



Planetary science: Lake flooding shaped ancient river valleys on Mars

初期の火星で起こった河谷の浸食の約4分の1は、湖の氾濫による洪水が原因だったという考えを示した論文が、Nature に掲載される。この論文に示される知見は、火星の河谷網の形成を理解するための手掛かりとなる基本的知見といえる。


今回、Timothy Goudgeたちは、かつて液体の水が古代の河谷を流れていたと考えられる地域で、火星の地形の形状と外形を調べた。lその結果、火星全体で、湖に蓄えられた水の氾濫が、古代の河谷網の形成に重要な役割を果たしていたことが分かった。実際、こうした氾濫型洪水は、初期火星の開析谷の体積の少なくとも24%の急速な侵食の原因であることが判明したが、湖沼氾濫型峡谷自体は、渓谷の総延長のほんの一部(約3%)にすぎなかった。


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.

doi: 10.1038/s41586-021-03860-1

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