Fig. 46 Mountain building

Mountain building is a complex process. Deep troughs of accumulated offshore sediment, volcanic rocks, bits of oceanic crust, and scrap s of foreign continents can all be swept against one continent and weld ed on as mountain ranges. Most of mountainous western North America consists of more than 50 suspect terrane s – mighty slabs of alien rock that independently rotated and migrated north along the western edge of North America.

Here are three major mountain-building processes.

1. Oceanic plate subduction below another oceanic plate – this process created the Aleutian Islands and other mountainous island arcs.