There are five main types of mountains: fold mountains like the Himalayas which are formed by colliding tectonic plates; volcanic mountains such as Mount St. Helens which are formed by volcanic eruptions; dome mountains like Mount Kea that form when magma forces up from below; plateau mountains in places like New Zealand which form from erosion of flat plains pushed upwards; and block mountains exemplified by the Sierra Nevada range that are created by cracks filling with rock and magma.