Volcanic Activity

A **Volcano** is a geologic fissure in the Earth's crust through which lava, volcanic ash and gases escape from a magma chamber to the surface. A caldera is a large, typically circular depression at the top of a volcano, formed when magma is expelled from below ground. Craters are also circular but smaller than calderas, created mainly by explosive excavation of rock during an eruption. The intensity, duration and frequency of magma eruptions vary, largely because of pressure buildup These eruptions primarily occur where tectonic plates meet and subduct. The Pacific Ring of Fire is a long chain of volcanoes and other tectonically active structures encircling the Pacific Ocean, formed by the subduction of oceanic plates beneath lighter continental plates. A laccolith is where magma is trapped beneath the Earth's surface, causing the rock above to bulge upward into a mushroom-shaped body.