Volcano

A volcano is a vent of some kind in the earth's crust through which magma is ejected. The magma frequently builds up in layers, resulting in the formation of mountains. Different types of magma produce different kinds of structures. Hot basaltic lava, which has low viscosity, tends to produce flat shield volcanoes because it can flow long distances before cooling. Andesite and dacite lava generally produce cones, like those seen in the cases of Mt. Fuji and Mt. Ranier, because the higher viscosity lava flows build up more dramatically near the vent