The thin crust of the earth protects the surface and continents from the hot molten rock inside. Tectonic plates move, or float, because of the intense heat underneath them. Himalaya and Karakoram mountain ranges were created by the collision of the two plates. Also earthquakes occur when two plates rub up against each other. The eruption of volcanoes is caused when two tectonic plates move away from each other. Moltem lava then fills the space between the two plates and builds up new crust on the ocean floor.