volcanoes. mount vesuvius, italy the cities of pompeii and herculaneum web site
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The Dead of Pompeii
• Plaster casts were made from “body cavities” found in the ash and lava covering Pompeii.
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
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”
Mount St. Helens, Washington, U.S.A.
• There was a major eruption in 1980.
• About 1000 ft of the mountain blew off.
• Web Site
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?
• At Convergent Boundaries: an area where plates move together.
• Washington State has an example of a convergent boundary.
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…?
• 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.
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
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