Hephaestus Fossae and Hebrus Valles

This VIS image is located in southern Utopia Planitia near Elysium Mons. It shows part of Hephaestus Fossae (bottom of image) and Hebrus Valles (top half of image). Both are complex channel systems that flowed northward. It has been proposed that Hephaestus Fossae formed by the release of melted subsurface ice during an impact event. Additionally, the nearby Elysium volcanic center created subsurface heating that may have played a part in creating both Hephaestus Fossae and Hebrus Valles to the north. Hephaestus Fossae is 633km long (393 miles).

The process that formed Hebrus Valles is unknown. Some of the channel features, as in this image, have the appearance of being formed by liquid flow on the surface of the plains. In other portions of the valles, there are pits and collapse features which appear to have formed by material falling into subsurface voids. This is a common feature in regions of volcanic activity where lava tubes run below the surface. Both water and lava probably contributed to the formation of Hebrus Valles. Hebrus Valles is 325km (202 miles) long.