Stratovolcanoes of the World, 2000

Stratovolcanoes (also known as composite volcanoes) are built of successive layers of ash and lava. The magma (molten rock) within the volcano is viscous and often contains trapped gas, causing explosive eruptions. The clouds of ash from the volcanic eruptions present a hazard to aviation. NOAA uses imagery from polar orbiting and geostationary satellites to detect the boundaries of a volcanic ash cloud, and estimates the altitude and movement of the ash plume. NOAA distributes Volcanic Ash Advisory Statements (VAAS) to warn aircraft pilots of hazardous ash clouds. Particles erupted into the stratosphere during major eruptions can change global temperature by several degrees, altering weather patterns and effecting global agriculture.

Approximately 85% of stratovolcanoes are located around the Pacific Ocean, forming what is called the “Ring of Fire.” Stratovolcanoes occur at the margins of tectonic plates, large sections of Earth's crust that move together. The continental plates, composed of less dense material, override the oceanic plates. Magma generated from the subducting plate rises and squeezes into cracks, eventually reaching the surface in a volcanic eruption.

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