Volcano Notes
Most volcanoes occur at the edges of the tectonic plates. Pressure from gases in the mantle squeezes the molten rock upwards. The surface of the Earth can swell like a big pimple until it cannot take any more pressure. It then explodes with lava, ash and steam bursting through the surface. Eruptions may come from a single vent, or from a group of vents. Others take place from long cracks called fissures. Most volcanoes just release clouds of steam, gas and ‘smoke’. Magma is molten rock that forms in a magma chamber deep under the surface, when emerges to the surface it is called lava. Lava flows down the volcano at speeds of less than 10 km/h and will later cool to form solid rock. Hot volcanic ash, steam and gases form a fast-moving (often 200 km/h) cloud that can reach incredible heights. Rain often then turns the ash into a lahar, a river of mud that can devastate anything downstream from it.
