Title: 18.1 Volcanoes; Divergent Volcanism & Hot Spots

Page #: 103Date: 4/29/2013

Students will be able to explain divergent volcanism.

Students will be able to identify and describe hot spots.

Divergent Volcanism

Pg. 502

Divergent Boundary: Where two plates move away from each other. • New ocean floor is produced as

magma rises to fill gaps.• Non-explosive.• Creates “Pillow Lavas” / “Pillow

Basalts.”• 2/3 of Earth’s volcanism occurs under

water along divergent boundaries at ocean ridges.

Divergent Volcanism

Hot Spots Pg. 502

Hot Spots: Create volcanoes far from plate boundaries.• Unusually hot regions of Earth’s mantle

where high temperature plumes of magma rise to the surface.

Hot Spot Volcanoes: As rising magma melts through crust it creates volcanoes.• Hot Spots: Form when magma plume

remains stationary as tectonic plate moves over it.

• Example: Hawaii.

Hot Spots

Hot Spots Pg. 503

Hot Spots and Plate Motion: Chains of volcanoes form over hot spots.• Rate and direction of plate motion can be

calculated from the position of volcanoes. • The further an island is away from a hot

spot, the older it is.

Hot Spots

Hot Spots. Islands get older as they get farther from hotspot.

Hot Spots Pg. 504

Flood Basalts: • Fissures: Long cracks in the Earth’s surface.• Fissures form when there is a hot spot under

continental crust.• Flood Basalts: When lava flows out of fissures

and onto continental crust.

Fissure Eruptions: Create plateaus - high flat plains.

• Examples: • Columbia River Basalts: Huge deposit of

basalt in the Northwest U.S. covers 170,000 km^3. Created by fissure eruptions.

• Deccan Traps: A plateau in India created by a huge fissure eruption. Made of 512,000 km^3 of basalt Enough to cover NY statet with 4 km of basalt.

Hot Spots

Columbia River Basalts

Deccan Traps

Anatomy of a Volcano

Pg. 505

Anatomy of a Volcano: Magma that reaches Earth’s surface is called “Lava.”

Conduit: Tube-like structure through which lava travels to Earth’s surface.

Anatomy of a Volcano

Conduit

Anatomy of a Volcano

Pg. 505

Vent: Opening through which lava emerges. Crater: Bowl shaped depression at top of

volcano around the vent.• Usually less than 1 km in diameter.

Anatomy of a Volcano

Anatomy of a Volcano

Pg. 505

Caldera: A large crater. May be up to 50 km in diameter.

• Usually form when magma chamber beneath volcano empties and the surface material collapses in on itself, leaving a large circular depression.

• May fill with water to form lakes.

Anatomy of a Volcano

Caldera Formation

Calderas

Types of Volcanoes Types of

Volcanoes

Pg. 507

Shield Volcano ･• Pool of magma breaks through

Earth's crust ･• Lava oozes out in layers ･• Forms new land ･• Wide, flat shape

Location: Hot Spots

Shield Volcano

Types of Volcanoes Types of

Volcanoes

Pg. 507

Cinder Cone Volcano• Violent explosions ･• Bursts forth with ash, cinder and lava

fountains ･• Rapidly built volcano ･• Not as high as composite or shield

volcano ･• Shaped determined by size of ejected

material

Location: On or very near large volcanoes.

Cinder Cone Volcano

Types of Volcanoes Types of

Volcanoes

Pg. 507

Composite Volcano ･• Most violent ･• Large cone shape ･• Magma explodes from volcano

because of hot gases and boiled water

• Excessive heat in magma ･• Alternating layers of ash, cinders and

lava

Location: Subduction Zones

Composite Volcano