Table of Contents Title: 18.1 Volcanoes; Divergent Volcanism & Hot Spots Page #: 103 Date: 4/29/2013

Objective Students will be able to explain divergent volcanism. Students will be able to identify and describe hot spots.

Divergent Volcanism 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 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. Islands get older as they get farther from hotspot.

Hot Spots 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.

Columbia River Basalts Deccan Traps

Anatomy of a Volcano 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.

Conduit

Anatomy of a Volcano 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.

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