Geology

Mountains result from the application of tectonic forces to rocks, usually sedimentary or volcanic rocks. (These may be changed to metamorphic rocks as mountain‐building progresses, and at times metamorphic rocks can be pushed into mountains). Mountain‐building on continents is associated with intense deformation, folding, and faulting, usually along convergent plate boundaries (Figure 1). An orogeny, or orogenesis, is the overall process by which a mountain system is built.

Figure 1

Mountain‐Building

Mountain ranges are groups of mountain peaks or ridges that form discrete topographic areas that are usually bordered by valleys or rivers. It takes tens or hundreds of millions of years to develop mountain belts, long chains of mountain ranges that can extend across continents or along their edges.

Much of our understanding of mountain‐building processes has come from studying ancient mountain belts that have since eroded to form flat erosional surfaces. Fieldwork in mountain ranges can be difficult because the rocks are complexly folded and faulted and because of the great changes in elevation. But such fieldwork can be productive because these features are important in the mapping and examination of the third dimension of the earth.