Volcano Notes.notebook March 01, 2017

Volcanoes

1. oceanic crust; oceanic and continental crust ex. Ring of Fire (Circum­Pacific Belt); Mt. St. Helens.

2. Divergent volcanism—mid ocean ridges; rift volcanism

ex. Iceland's volcanoes

3. Hot spots—not near plate boundaries; unusually hot regions of earth’s mantle where mantle material rises to the surface; island chain forms as plate moves over hot spot

ex. Hawaiian Islands

Where do Volcanoes Form?

Volcanic EruptionsWhat determines the type of eruption?

• Composition of magma

• Temperature of magma

• Amount of dissolved gases in magma

Water vapor and CO2

Provides the force to extrude lava

• Viscosity of magma

Hotter magma—less viscous (thinner)

Silica content (high content—high viscosity)

More viscous (thicker)—more violent the eruption

­­Thinner magma (oceanic); thicker (continental)

• vent—opening in the earth’s crust through which lava flows • crater—bowl shaped depression around a vent at the top of a volcano

• caldera—depression that forms when the top or side of a volcano collapse into the magma chamber

• lava dome—masses of lava pile up around the vent

Parts of a Volcano

Types of Volcanoes

• Shield Volcanoes

> Form on oceanic plates

> Gentle slopes

> non­explosive eruptions

> ex. Hawaiian Islands

• Composite Volcanoes

> Largest volcanoes

> Most violent eruptions

> Form at convergent oceanic­continental boundaries (subduction zones)

> Ex. Mount St. Helens.

• Cinder Cones

> steep­sloped hill of cinders (or scoria)

> smallest volcanoes

Volcano Status

• Active ­­ has erupted in recorded history.

> DYK? ­­ There are 539 active volcanoes in the world.

• Dormant ­­ Last eruptions hundreds of years ago.

• Extinct ­­ Has not erupted in millions of years.