Volcanoes

Mount Vesuvius, Italy

The Cities of Pompeii and Herculaneum

Web Site

The Dead of Pompeii

• Plaster casts were made from “body cavities” found in the ash and lava covering Pompeii.

The Dead Of Pompeii

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Pompeii

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Taken from Digging up the Past - Pompeii & Herculaneum, Peter Hicks, (Wayland, East Essex, 1995)

Volcanoes in the United States

• VolcanoWorld - List of North American

Mt. Lassen, CA

Three Sisters, Bend, OR

Volcanoes in the United States

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Mt.Lassen, California

Alaskan Volcanoes

• A Lake on Mt. Martin, Alaska

Alaskan Volcanoes

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57 Alaskan Volcanoes

• The Aleutian Islands are a chain of more than 300 small volcanic islands in the Northern Pacific Ocean.

• Unalaska Island, Alaska, U.S. pop. 6,000

Volcanoes

• A Volcano is an opening in Earth’s surface that often forms a mountain when lava and ash build up.

• Most volcanoes are dormant. • ( dormant = not active; no gasses, no lava)• 600 volcanoes are active.• In1991, Mount Pinatubo erupted in the

Philippines. It was the largest of the 20th Century.

Mount Pinatubo

Kilauea, Hawaii

• Kilauea is the most active volcano on Earth. It has been erupting for at least 250 years.

• Kilauea is formed over a “hot spot”

Kilauea, Hawaii

• The tectonic plate moves over a “hot spot”.

Kilauea

Kilauea

• Hula for Pele, goddess of the volcano

Kilauea

Kilauea

• 500 acres are added to the island each year.

Mount St. Helens, Washington, U.S.A.

• There was a major eruption in 1980.

• About 1000 ft of the mountain blew off.

• Web Site

Mt.St.Helens

• This is the view as it is now, after the eruption.

What causes a Volcano?

• Magma is less dense than the rock around it; so it slowly rises.

• After thousands of years, magma flows out an opening called a vent.

• A crater is a walled area that builds up around a vent.

Inferno Crater, New Zealand

Where Do Volcanoes Occur?

• At Divergent Boundaries : an area where the Earth’s plates are moving apart.

• Iceland is an example of a divergent boundary

Where Do Volcanoes Occur?

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Where do volcanoes occur?

• At Convergent Boundaries: an area where plates move together.

• Washington State has an example of a convergent boundary.

Plate Boundaries

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Where …?

• Subduction Zones : convergent boundaries where one plate goes under another.

• Costa Rica has a subduction zone where the Cocos plate moves under the Caribbean plate

Where…Subduction Zones?

Where…?

• At Hot Spots : In the middle of a tectonic plate, magma comes from deep in the Earth’s mantle. The plate moves over the hot spot over millions of years.

• The Hawaiian Islands were formed this way.

Hot Spots

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Energy From The Earth

• Geothermal Energy – Heat from magma heats water.

• The steam turns a turbine to generate electricity.• Hot Dry Rock ( HDR) : no magma, water is

pumped into hot, dry rock.• Rock is hotter as the depth into the Earth

increases. Electricity is made with the resulting steam. No carbon dioxide is produced. WEB

Geothermal Energy

Geothermal Energy

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Types of Volcanoes

• Shield Volcanoes – a broad volcano with gently sloping sides.

• They have quiet eruptions.

• Basaltic lava layers build up.

• The Hawaiian Islands are examples of shield volcanoes.

Mauna Loa

Types of Volcanoes:

• Cinder Cone Volcanoes – a steep-sided volcano.

• Violent Eruptions

• Lava cools and hardens to form tephra ( ash ,cinders, rocks)

• Arizona has a cinder

cone volcano.

Cinder cone in Mexico

Types of Volcanoes

• Composite Volcanoes – alternating layers of lava and tephra.

• Quiet and violent eruption periods.

• Explodes = tephra, Quiet = lava flows

• Mount St. Helens in

Washington is a

composite volcano.

Shishaldin, Alaska

Types of Magma

• Basaltic magma = has less silica, is fluid, and produces quiet eruptions…has little water.

• Granitic magma = makes violent eruptions. • Granitic magma is thick and contains a lot of

silica. It blocks vents and causes pressure to increase…has a large amount of water.

• Explosive Eruptions = water and carbon dioxide trapped in magma cause explosions.

Volcano Vocabulary: Define these words:

• Caldera = a collapsed crater

• Batholith= large area of rock, a lake.

• Laccolith= a sill which forms a dome.

• Dike= vertical rock structure

• Sill= horizontal rock layer

• Volcanic Neck = the central core of a volcano

Recent Eruptions

• Mount Etna – Sicily, Italy – May 2007

• Etna is Europe’s largest volcano at 10,000ft.

• It is a composite volcano.