VOLCANOES

5th grade, A Closer LookMacMillian/McGraw-Hill

Where are Volcanoes found?

volcano- opening in Earth's crust most are located at plate boundaries Ring of Fire surrounds Pacific Ocean

PARTS OF VOLCANOAll volcanoes have at least one vent (opening).Crater- cup-shaped depression may form around a ventMagma chamber- where magma collectsLava- when magma reaches Earth’s surface

Caldera- a hole forms beneath the magma chamber, the magma leaks out and the chamber collapses inside itself.

Dike- Some magma hardens in vertical cracks

Sill- forms when magma hardens between horizontal layers of rock

Laccolith- when sills don’t spread horizontally, instead they push upward and form a dome shape

Batholith- largest/deepest underground magma formations. They are huge, irregularly shaped, reaches deep into crust.

TYPES OF VOLCANOES Shield volcanoes-

built by thin, fluid lava

spread over large area

broad base, gently sloped sides

Cinder-block volcanoes

•Built by thick lava•Thrown high in the air, falls as chunks•form cone shape with narrow base and steep slopes

Composite Volcanoes

Built by layers of ash and cinders, sandwiched between layers of hardened lava

Eruption- outpouring of lava, ash, gases, or combination of these

VOLCANOES ERUPT WHEN ONE PLATE IS PUSHED UNDER ANOTHER PLATE.

Rocks push down, heat and melt.

Magma forms and pools in the magma chamber under the crust.

Cracks form above the chamber or pressure grows too great and magma rushes upward toward the Earth’s surface.

ACTIVE, DORMANT, EXTINCT

Active volcanoes- currently erupting or have recently erupted

Dormant volcanoes- doesn’t erupt for a long time

Extinct volcanoes- dead/stopped erupting long ago