Global volcanoes map. World map showing the location of volcanoes (red triangles) around the world. The volcanoes are concentrated along the boundaries (yellow lines) of the tectonic plates that make up the Earth's crust. The continents (black), oceans (blue) and continental shelves (light blue) are also shown. Tectonic plates move over the molten rock below them, colliding with and moving past, under and over each other. At the point where the tectonic plates are destroyed, molten rock can move upwards, forming a volcano.