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What are volcanoes? We know of them as big mountains spewing fountains of fiery magma from their peaks. We even know of the more famous ones such as Mt. Vesuvius in Roman times and Mt. St. Helens in our recent memory. However there is more to the story than what we commonly know.
To understand volcanoes we need to understand the composition of the earth and plate tectonics. The earth can be best explained as a ball of molten rock with a cooled crust. Pretty much like a fruit pie. However the crust is the earth’s surface where we live. The Earth’s crust is broken up into plates. These plates float on the ocean of molten rock beneath surfaces called the mantle. Like the normal ocean magma (molten rock) in the mantle also has currents. The hotter magma rises away from the Earth’s core while the cooler magma sinks back towards it. This creates the current that moves the plates of the Earth’s surface making plate tectonics.
Tectonic plates are moving away, diverging or colliding, converging. These two conditions make volcanoes. A volcano is a vent or crack in the Earth crust that allows magma and hot gases to escape. When the tectonic plates diverge new magma wells ups to make the newer parts of the Earth’s crust. When plates converge the common occurrence is that one plate is forced beneath the other. This is called subduction. The incredible force involved melts the rock of the subducted plate creating magma. This is the other condition under which a volcano is made.
A great way to look at is that where ever plates’ boundaries are you should find a volcano. The location can be on a continent like in Europe or North America. However, the most interesting volcanoes will be in island chains. These occur in locations not at the boundaries of plates.
Ocean volcanoes are important because they help to make new islands. There are certain places that are not tectonic boundaries. These are regions of the Earth’s mantle called hot spots. They are places where rising magma is highly focused and melt the crust. This creates a new volcanic mountain on the ocean floor. Over time the volcano grows in stature until an island is born above the ocean’s surface. If a plate passes over a hot spot, it can over time create island chains such as the Hawaiian Island chain.
If you enjoyed this article there are several others on Universe Today that you will enjoy. There is a great article about extinct volcanoes. There is also a great article on three types of volcanoes.
U.S. Geological Survey