Volcanoes form when there is an opening in the Earth’s crust and have four main parts – pipe, vent, crater and cone. The vent is the actual opening and the pipe is the passage through which the molten lava pours from the Earth’s core to the surface. Volcanoes are like mountains, some of which are very high, forming the cone, which is made up of the ash and lava that dries as it reaches the surface. At the top of a volcano, there is a crater, which is a bowl-shaped depression.
Scientists who study volcanoes are called volcanologists. They have grouped the volcanoes of the world into different categories depending on their composition. These categories are:
- Composite – These are also called strato volcanoes. They are made up of alternating layers of lava and rock. Some of them are impressive
snow-capped peaks and are often so inactive that many experts believe them to be extinct. When they do erupt, they are very explosive because the magma tends to clog the pipe. When the gases build up, the crater explodes. Not all of these volcanoes are shaped like cones. Some of them are round and some may have several craters designating several openings. Examples of this type of volcano include Mount Hood, Mount Rainier and Mount Fuji.
- Shield – These are really massive volcanoes built up over the centuries of running flows of lava. They may have one central vents or several vents and the cone is very broad with gentle slopes. The hotspots causing the volcano may actually be very far away from the site of the volcano itself. The eruption of these volcanoes is usually in the form of a low explosion in which the cinders form around the site of the vent. Examples of this type of volcano include Mauna Loa and Kilauea in Hawaii.
- Cinder Cones – These smaller volcanoes are steep hills shaped like a cone and are the most commonly found volcanoes in the world. They form from cinders and can form very quickly, but are rarely higher than 250 feet. They can change shape several times and although the power of the eruption varies, there have not been any lives lost in these eruptions. An example of a cinder cone is that in Paricutin in Mexico.
- Splatter Cones – When a volcano erupts with low force, the lava shoots into the air and comes back to rest in basically the same location. The lava splatters in the area and forms a smaller steep volcano.
- Complex – Complex volcanoes are made up of several flows, cones and vents. The term refers to a system of volcanoes with two or more vents.