Topographic inversion is a process where geologic features that were once low-lying, like impact craters or riverbeds, become elevated over time, like mesas or ridges. In this process, a crater or channel is filled with lava or sediment that becomes lithified.

If this infill is more resistant to erosion than the surrounding landscape, the less-resistant material can be eroded away by wind or water. The former crater or valley fill, being more resistant, remains elevated as the landscape around it lowers. The original low-lying feature becomes a mesa or ridge.

In this image, an ancient river network and nearby impact craters have undergone topographic inversion. Impact craters contain round mesas within them, and the stream channel is defined by a network of ridges. Studies of ancient stream channels and impact craters (and their inverted counterparts, like mesas and ridges) help scientists understand when and where liquid water was present on the surface of Mars and the potential for the past existence of habitable environments on the planet.

Written by: Chris Okubo  (18 December 2025)