A Volcano is a vent in Earth's crust through which melted or molten rock flows

Scientists have learned that the movement of Earth's tectonic plates causes the formation of volcanoes and the eruptions that result

Volcanoes can form along convergent plate boundaries

Lava erupts along divergent plate boundaries

Volcanoes that are not associated with plate boundaries are called hot spots

The Ring of Fire represents an area of earthquakes and volcanic activity that surrounds the Pacific Ocean

In larger populated areas the United Sates uses the USGS

Composite volcanoes - are large, steep-sided volcanoes that result from explosive eruptions of andesitic

volcanic ash - tiny particles of pulverized volcanic rock and glass-high into the atmosphere

Silica is the main chemical compound in all magmas

Magma that has a high silica content has a high viscosity

Magma that has a low silica content also has a low viscosity

Effects of Volcanic eruptions are lava flows, ash fall, mudflows

Volcanic eruptions affect climate when volcanic ash in the atmosphere blocks sunlight

pahoehoe-smooth, shiny surface, usually dark colored

Quiet - pours out runs down the side of the volcano; pahoehoe - fast moving low viscosity, aa - slow moving high viscosity

Explosive- start with vent blocked, high viiscosity lava, pressure releases at weak point(crater)

can damage or destroy communites land near volcano

few building were repaired many left the way they were