A percipitate is formed when a slightly soluble substance becomes insoluble and separates from a solution due to heat or a chemical reaction. The term is used to indicate the act of forming a solid and for the substance that is precipitated out of a solution. Light rock froth produced by the violent separation of gas from lava. Because of the many gas bubbles, some of this froth is so light that it floats on water. A high-density mass of gases, hot ash, and larger material that flows rapidly down the sides of the volcano.
Flows tend to be confined to valleys.
Because of the speed at which they travel and the intense heat, pyroclastic flows and surges are one of the most dangerous hazards posed by volcanoes. Because surges are low density, they tend to spread over large areas and jump ridge crests easily. A volcano, which is not active, but is still registering seismic activity. A place where a large supply of magma collects. A zone around the perimeter of the Pacific Ocean containing about two-thirds of the world s active volcanoes.