A volcano is simply an opening in our planet’s crust through which magma can get out. Volcanoes take many shapes and sizes; they are not just the typical cone shaped volcano we often see portrayed. The term volcano actually comes from Vulcano, an Italian volcanic island, which was named after Vulcan, the Roman god of fire. Ancient civilizations, such as the Greeks and Romans, used to believe that volcanoes were caused by the actions of the gods or other supernatural events.
Additionally, volcanoes exist under icecaps and in the ocean rather than just on land. Volcanoes under the ice are known as subglacial volcanoes. Since the lava has no place to go underneath the ice, it forms flat topped mountains. Submarine volcanoes, which are found in the oceans, are actually quite common. Some of the Hawaiian Islands are examples of submarine volcanoes that reached the surface and became islands. Different types of volcanoes include shield volcanoes, fissure vents, composite volcanoes, and supervolcanoes to name a few.
Volcanoes are not only different in shape. They also have different types of lava, and the type of lava a volcano has actually affects its shape. The types of lava are felsic, intermediate, mafic, and ultramafic. Felisc lava is very high in silica. Intermediate lava, also known as andesitic lava, is lower in silica and aluminum and higher in magnesium and iron. Mafic lava, or basaltic lava, is high in iron and magnesium. Ultramafic lava is basically a superheated form of mafic lava. There are also other factors that determine how lava will act.
Most volcanoes occur where tectonic plates converge and diverge because it is easier for the crust in these areas to crack. Volcanoes can also been found where the Earth’s crust is thinner. This explains why there are so many volcanoes in certain areas of the world, such as the Ring of Fire in the Pacific Ocean.
Some of the most famous volcanoes include Mount Vesuvius in Italy; Mount Fuji, which the highest point in Japan; Mount St. Helens, which erupted in America in 1980; and Mauna Kea in Hawaii, the tallest volcano in the world.
Volcanoes can cause major damage to a region as well as take lives. In some of the most destructive volcanoes, tens of thousands of lives have been taken although many of those deaths were caused by natural disasters that resulted from the volcanoes. Often, volcanoes are so destructive because they can also trigger other natural disasters such as tsunamis and earthquakes. Additionally, the ash from a volcano can spread for many miles and cause damage to people’s lungs.
Astronomy Cast has an episode on volcanoes.
USGS Volcano Hazards Program