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Mount Vesuvius, Italy
The Cities of Pompeii and
Herculaneum
The Dead of Pompeii
• Plaster casts were made from “body
cavities” found in the ash and lava covering
Pompeii.
The Dead Of Pompeii
•
Pompeii
•
Taken from Digging up the Past - Pompeii &
Herculaneum, Peter Hicks, (Wayland, East Essex, 1995)
Volcanoes in the United States
• VolcanoWorld - List of North American
Three Sisters, Bend, OR
Mt. Lassen, CA
Volcanoes in
the United States
•
Mt.Lassen, California
Alaskan Volcanoes
• A Lake on Mt. Martin, Alaska
Alaskan Volcanoes
•
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
Mount Pinatubo
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.
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?
•
Where do volcanoes occur?
• At Convergent Boundaries: an area where
plates move together.
• Washington State has an example of a
convergent boundary.
Plate Boundaries
•
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
•
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
•
•
Mauna Loa
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.
Cinder cone in
Mexico
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.
Shishaldin, Alaska
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.
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.