What type of landforms are horsts and grabens classified as?

Horsts and grabens are classified as landforms formed by faulting due to tectonic processes that result in the movement of the Earth's crust. These structures are created when the forces of tectonic stress cause fractures in the Earth's surface, leading to blocks of crust being elevated or lowered. A horst is an elevated block of the Earth's crust that is surrounded by lower areas, while a graben is a block that has subsided relative to the surrounding land. This system of uplift and subsidence typically occurs in areas experiencing tectonic activity, where the tectonic plates are pulling apart or colliding, leading to the creation of these distinct geological features.

The other types of landforms mentioned, such as those formed by erosion, deposition, or volcanic activity, do not apply in this context. Erosion involves the wearing away and transportation of materials, deposition pertains to the accumulation of materials, and volcanic activity is related to the movement of magma and the formation of features like volcanoes or lava plateaus, which is separate from the processes that create horsts and grabens. Thus, faulting is the correct classification for these types of landforms.