Block Mountain is an uplifted section of crust with one or more faulted boundaries. They are also known as horsts.
Block Mountains are defined as an area of high relief which is bounded on most sides by faults and which has been either uplifted by earth-movement, or left elevated by the sinking of surrounding areas. Black Forest and Vosges Mountains are the fine examples. The Nilgiris in South India are also Block Mountains.
Block Mountains are generally formed due to tensional forces. But sometimes compression also produces such mountains. They are generally straight in form, and are characterized by the presence of fault scarp.
In their extent, they are very limited. Faulting is the main cause for the formation of Block Mountains that is why they are also known as fault-block Mountains. Some block mountains are associated with rift valleys. Several such mountains are found is East Africa.