A volcano that is erupting. Also, a volcano that is not presently erupting, but that has erupted within historical time and is considered likely to do so in the future.
Fine particles of pulverized rock blown from an explosion vent. Measuring less than 1/10 inch in diameter, ash may be either solid or molten when first erupted.
The shell within the earth, some tens of kilometers below the surface and of undefined thickness, which is a shell of weakness where movements take place to permit pressure adjustments.
A body of rock that contains significant quantities of water that can be tapped by wells or springs.
A large mass of material or mixture of material falling or sliding rapidly under the force of gravity. _____________ often are classified by their content, such as snow, ice, soil, or rock avalanches. A mixture of these materials is a debris avalanche.