Volcanic flows are streams of molten rock that are expelled from a volcano during an eruption. The molten rock is known as lava, and is composed of magma that has been heated to extreme temperatures. Lavas, which is the term used to describe these volcanic flows, can travel at speeds of up to 100 kilometers per hour and can reach temperatures of up to 1, 000 degrees Celsius. They can cause significant destruction when they come into contact with buildings, vegetation, and other structures.