What is a Volcano?

The Earth is covered with a variety of different features. Oceans, plains, rivers, valleys, mountains, and one of the most dramatic, volcanoes. Named for Vulcan, the Roman god of fire, Volcanoes are one of the most powerful, spectacular forces on earth. Volcanoes can build, or destroy – but where do they come from? The surface of the Earth is cool and solid, but underneath, a thick layer of hot, molten rock churns. This molten rock is called magma. Sometimes, a crack or a break in the cool surface layer – known as the crust – allows magma to rise to the surface. There are two main ways that volcanoes are formed. First, volcanoes may form at the boundaries of tectonic plates. Tectonic plates are sections of the earth’s crust that float on the layer of magma beneath, known as the mantle. Where two plates meet, they may either pull apart, allowing magma from the mantle to come up, or they may push together, shoving some of the crust beneath to be melted into magma and pushing other pieces of the crust up to form new mountains. The new magma beneath the crust starts creating pressure, and once enough pressure has built up it can burst through the crust – – as an erupting volcano. The second way volcanoes may form is due to ‘hotspots.’ Scientists believe that when a volcano forms away from the edge of a tectonic plate, it is either because the mantle beneath is unusually hot, or because the crust in that area is unusually thin, allowing the magma to melt its way through to the surface. Magma that reaches the surface is called ‘lava.’ Either way, the result is the same: Volcanoes!

Volcanoes are typically mountains, and although you may picture a volcano a certain way, they actually form a variety of different structures. The first type of volcanoes is cinder cones. Cinder cones are some of the most common volcanoes. They are fairly small, steep-sided cones, made of loose rocks, ash, and debris that were thrown out during the eruption. Unlike other volcanoes, cinder cones usually have a single opening through which magma escapes. The second type of volcanoes are shield volcanoes. Shield volcanoes have low profiles and shallow-sloping sides. Unlike cinder cones, shield volcanoes can be very, very large because they are so short and wide – they are the largest type of volcanoes on earth – but they are usually less dangerous than other types. That’s because instead of forceful eruptions, shield volcanoes are formed by very runny lava that flows a long way. Third, there are composite volcanoes. Also known as ‘stratovolcanoes’ because they are made of alternating layers built up through different eruptions, composite volcanoes can grow to be very large and may be very dangerous. Some famous volcanoes, like Mt Fuji in Japan, and Mt Vesuvius in Italy, are composite volcanoes. There are other types of volcanoes, too, like fissure vents, lava domes and lava tubes. When the lava from volcanic eruptions cools, it hardens into rock. These rocks are igneous, or formed from magma and lava. Different types of lava, different types of eruption, and different speeds of cooling all produce different kinds of rock. One interesting type of volcanic rock is called pumice. Pumice is full of little air bubbles, which makes it so light that it can actually float on water. Another interesting type of volcanic rock is obsidian. Obsidian is hard and shiny, like glass, and can be made into blades and tools with a very sharp edge. There are many other types of volcanic rock, as well! Volcanoes that may still erupt are called active. Volcanoes that will probably not erupt again any time soon are called dormant – a word that means ‘sleeping.’ Scientists have gotten better at predicting when a volcano is going to erupt, but sometimes volcanoes still take people by surprise. Beautiful and dangerous, volcanoes are an important part of our living world. They can create new land, they can destroy and even kill…but in the end, they are a powerful reminder that our planet is still wild, and always changing. I hope you enjoyed learning about volcanoes today. Goodbye till next time!