A directed blast is a laterally directed explosion of the volcano caused by rapid release of internal pressure. Most directed blasts are caused by a slope failure of newly erupted lava domes or sector collapse of the summit edifice into a debris avalanche, resulting in rapid depressurization of a shallow magma body. Directed blasts can destroy structures throughout a large radial zone extending 10 to 25 kilometers away from the source of the blast. (RI 2004-3)
