Inverted relief

Inverted relief, also called inverted topography or topographic inversion, describes landscape features whose elevation has reversed relative to their surroundings. It typically happens when a low part of the landscape, such as a valley or depression, fills with lava or sediment that hardens into rock more resistant to erosion than the material around it; as the surrounding, softer material erodes away over time, the once-low, now-hardened feature is left standing higher than its surroundings, so former valleys can end up as ridges. The same effect can arise from coarse sediment left in a depression while wind strips away finer material elsewhere, from mineral cementation such as a duricrust hardening a low area, or from folded rock where an eroded anticline exposes softer rock that wears down faster than the syncline beside it; the pattern has been documented on Earth, including at Table Mountain in California and in Cape Town, and is also widely seen on Mars, where inverted channels record ancient water flow.