A volcano is an opening (usually in a mountain) in the Earth’s surface (the crust) from which gas, hot magma and ash can escape. The crust is made of “tectonic plates” – giant blocks that fit together like a jigsaw puzzle and slide on top of a hot layer of molten rock called the mantle. Volcanoes are often found at meeting points of the tectonic plates, and also at “mantle plumes” which are super hot areas of rock inside the Earth – “hot spots” create a pathway for molten rock in the plate to come to the surface. The molten rock inside a volcano is called magma. Magma that escapes through a volcano and reaches the surface of the earth is called lava. How syrupy or watery the lava is depends on the type of rocks being melted. Thicker magma and lava tends to cause more explosive eruptions, while more watery kinds tend to ooze out and create gradually sloping volcanos.