eruptions are steam-driven explosions that occur when water beneath the ground or on the surface is heated by magma
, hot rocks, or new volcanic deposits (for example, tephra
and pyroclastic-flow deposits). The intense heat of such material (as high as 1,170° C for basaltic
lava) may cause water to boil and flash to steam, thereby generating an explosion of steam, water, ash
, blocks, and bombs.