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The Formation and Types of Volcanoes

A volcano is a rupture in the crust of a planet that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates are diverging or converging. For example, the Ring of Fire in the Pacific Ocean is a region of high volcanic and seismic activity due to the movement of tectonic plates. However, volcanoes can also form in the middle of a plate at locations called "hotspots," where magma pushes up from deep within the Earth's mantle. The Hawaiian Islands are a well-known example of a volcanic chain created by a hotspot.

The characteristics of a volcanic eruption and the shape of the volcano itself are determined primarily by the composition and viscosity of the magma. Magma that is high in silica is very viscous, or thick, and tends to trap gases. This leads to a buildup of pressure and results in explosive eruptions that create steep-sided, conical landforms known as composite volcanoes. Mount Fuji in Japan is a classic example. In contrast, magma with a lower silica content is more fluid. It allows gases to escape easily, leading to effusive, or gentle, eruptions of flowing lava that build wide, gently sloping shield volcanoes.

Beyond their shape and eruption style, volcanoes are also classified based on their frequency of eruption. They are categorized as active, dormant, or extinct. An active volcano is one that has erupted in recent historical times and is expected to erupt again. A dormant volcano is one that has not erupted for a long time but has the potential to become active. An extinct volcano is considered very unlikely to erupt again. These classifications are not always absolute, as it can be difficult to determine a volcano's true potential for future activity.