The importance of lake breach floods for valley incision on early Mars.

The surface environment of early Mars had an active hydrologic cycle, including flowing liquid water that carved river valleys1-3 and filled lake basins4-6. Over 200 of these lake basins filled with sufficient water to breach the confining topography4,6, causing catastrophic flooding and incision of outlet canyons7-10. Much past work has recognized the local importance of lake breach floods on Mars for rapidly incising large valleys7-12; however, on a global scale, valley systems have often been interpreted as recording more persistent fluvial erosion linked to a distributed Martian hydrologic cycle1-3,13-16. Here, we demonstrate the global importance of lake breach flooding, and find that it was responsible for eroding at least 24% of the volume of incised valleys on early Mars, despite representing only approximately 3% of total valley length. 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 floods should be considered when reconstructing the formative conditions for Martian valley systems.