When lava is extruded under water, the surface of a lava flow cools quickly to form a thin skin around the lava flow. This thin skin cracks easily because of the pressure of the still molten lava inside. Bulbous globs of lava extrude from the cracks, cool quickly, and pile up on one another like a large pile of pillows. Flood basalts are common in northeastern California and eastern Oregon and Washington. Volcanoes - Sloping piles of volcanic rock that erupt from and surround a central vent.
Examples are volcanoes in Hawaii and Iceland.
Produces the least destructive eruptions. Cinder cone - Made of mostly pyroclastic material, have steep slopes, and are small. Explosive and destructive eruptions that produce pyroclastic flows are typical of this type of volcano. In 1980, Mount Saint Helens in Washington produced a well documented pyroclastic flow that killed several people. Most composite volcanoes have one or more craters.