There are four main types of landforms: mountains, plateaus, and plains. Mountains form through volcanism or faults in the earth's crust and are categorized as block, fold, residual, or volcanic mountains based on their formation. Plateaus are high plains that can be intermontane, piedmont, or continental based on their surrounding terrain. Plains form through deposition by rivers (alluvial), glaciers (glacial), seas (coastal), or uplift of continental shelves (structural).