Chapter 18 Earth science Alex Newell 3/1/10

Volcanic activity Magma Types of magma Viscosity Intrusive activity Plutons and tectonics Volcanoes Volcanic material

Magma All volcanoes are fueled by magma deep beneath Earth’s surface

Types of magma Basaltic magma- Basaltic magma- has the same composition as basalt

Andesitic magma Has the same composition as andesic

Viscosity The viscosity of magma and of its surface counterpart, lava, depends on both temperature and composition

Plutons Intrusive igneous rock bodies

Laccoliths A mushroom- shaped pluton with a round top and flat bottom

Volcanoes Lava erupts through an opening in the crust called a vent

Volcanoes At the top of a volcano, around the vent, is a bowl shaped depression called a crater

Types of volcanoes Shield volcano- a mountain with a broad, gently sloping sides and a nearly circular base Shield

Cinder-cone volcanoes Forms when material ejected high into the air falls back to Earth and piles up around the vent

Composite volcanoes Form when layers of volcanic fragments alternate with lava

Volcanic material Rock fragments thrown into the air during a volcanic eruption are called tephratephra

Pyroclastic flow Rapidly moving volcanic material