Types of Mountains

Although each mountain range has a unique set of characteristics, a particular mountain can be structurally classified as upwarped, volcanic, fault‐block (horst and graben), or folded (complex) (Figure 1). It is not unusual to find all four categories of mountains within a single mountain range.

Figure 1

Types of Mountains

Upwarped mountains are generally the result of broad arching of the crust or sometimes great vertical displacement along a highangle fault. The Black Hills in South Dakota and the Adirondack Mountains in New York are upwarped mountain ranges. These mountains are more rounded and show some unloading features such as exfoliation. Volcanic mountains are the accumulations of large amounts of volcanic lavas and pyroclastic material around the volcanic vent, such as seamounts and stratovolcanoes. The Hawaiian and Aleutian Islands are volcanic mountains. Fault‐block mountains result from tensional stress. They are bounded by high‐angle normal faults, and usually form a series of horsts and grabens. Broad crustal uplift (possibly a result of subduction stresses or mantle upwelling) can stretch and break the crust, creating fault zones along which the blocks move or slide. Uneven tectonic uplift can tilt the blocks. A good example of fault‐block mountains are those in Nevada that are part of the Basin and Range region. Folded, or complex, mountains are created by intense compressional forces that fold, fault, and metamorphose the rocks, resulting in many of the world's biggest mountain belts, such as the Himalayas.