Important Facts on Volcanoes 11-30-07 Entry #11

A Volcano is a mountain with a vent, cooled lava, ash, and cinders. The difference between a volcano and a mountain is the activity of the plates below the surface (making magma or not).

Volcanoes are constructive Volcanoes are constructive. They add new rock to existing land and form new islands. Magma- molten rock and gases under the crust. Is called lava once it is outside of the Earth. Volcanoes are mostly found at plate boundaries along the Pacific Ocean called the “ring of fire”.

Quiet- gases flow gently, low silica, thin runny lava. Hot spot areas. When a volcano erupts magma rises to Earth’s surface and exits through an opening called a vent. Occur at divergent boundaries or convergent boundaries with subduction takes place. Types of Eruptions: Quiet- gases flow gently, low silica, thin runny lava. Hot spot areas. Explosive- gases don’t escape, but build up and increase pressure. Thick lava, high in silica—burst of ash, gases, lava, and cinders is called a pyroclastic flow.

Different types of volcanic eruptions form different types of volcanoes. Volcanoes made mostly of cinders and other rock are called cinder cones and form from explosive eruptions. Volcanoes composed of quiet flows are called shield volcanoes. Volcanoes built up of alternating layers of rock particles and lava are called composite volcanoes.