What are a graben and horst?

A graben and a horst are geological terms used to describe different types of features that can form along faults in the Earth’s crust.

Graben: A graben is a type of down-dropped block of land bounded by two parallel faults. It forms when the Earth’s crust is pulled apart along a fault, and the central block sinks relative to the blocks on either side. This results in a depressed block of land with steep fault scarps on both sides. Grabens are often elongated and can be found in areas of tectonic extension, such as rift valleys and divergent plate boundaries.
Horst: A horst is the opposite of a graben. It is an upthrown block of land bounded by two parallel faults. It forms when the Earth’s crust is uplifted along a fault, and the central block is elevated relative to the blocks on either side. This results in a raised block of land with steep fault scarps on both sides. Horsts can form in areas of tectonic compression, such as convergent plate boundaries and areas with folding and faulting.
Both grabens and horsts are common features associated with faulting and can be found in various geologic settings around the world. They are important in understanding the tectonic processes and structural geology of a region, and they have significant implications for landforms, landscapes, and natural resources.