Horst (geology)

A horst is a raised block of the Earth's crust that has been uplifted relative to its surroundings by faulting. It is a common feature in regions experiencing extensional tectonics, where the crust is being stretched and pulled apart. Horsts are typically bounded by normal faults, which are fractures in the rock where the hanging wall (the block above the fault) has moved downward relative to the footwall (the block below the fault).

The formation of a horst is a result of differential movement along these normal faults. As the crust is extended, blocks of crust subside along the faults, creating grabens (down-dropped blocks). The intervening blocks that remain relatively elevated are termed horsts. Horsts can range in size from a few meters to many kilometers in width and length.

The term "horst" originates from the German word for "heap" or "mound." Topographically, horsts often appear as ridges, hills, or mountains, although the actual topography can be influenced by erosion and other geological processes. They may be composed of various rock types, depending on the geological history of the region.

Horsts and grabens often occur together in what is known as a "horst and graben system," forming a distinctive landscape characteristic of areas undergoing crustal extension, such as rift valleys.