A volcano is event in the earth, which erupts when hot liquefied rock or magma moves to the earth's surface, pouring out as lava. The latter may flow out as a liquid, or it may explode from the vent as solid or liquid particles accompanied by superheated gases. Ash and cinders form a cone around the vent. There are several types of volcanoes. The most fluid magnus erupt quietly and flow from the vent to form gently sloping shield volcanoes. The name shield volcano comes from their resemblance to the shields of early germanic warriors. The lava flows from shield volcanoes are usually only one to ten meters thick, but may extend for great distances from the vent. The volcanoes of hawaii and iceland are typical volcanoes of this type. Cinder cone. Volcanoes are formed when magnus, with high gas contents and high viscosity are blown high into the air. During an eruption, the magma falls as volcanic bombs, which accumulate around the vent and form steep sided cones called errors. Large basin, like depressions, are formed when a violent eruption blows the top off of an existing cone, or when the center of a volcano collapses. One famous called era covers much of yellowstone national park. Six hundred thousand years ago, there was a huge volcanic explosion which devastated the landscape.