Transcript What is a volcano?

Magma Magic
What is a volcano?
• A volcano is any place where gas, ash, or melted rock
come out of the ground.
• Many volcanoes are dormant, meaning an eruption has
not occurred in a long period of time.
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Video on volcanoes
http://studyjams.scholastic.com/studyjams
/jams/science/rocks-mineralslandforms/volcanoes.htm
What is a volcano?
• Volcanoes form as rock below Earth’s surface
melts. The melted rock, called magma, is less
dense than solid rock, so it rises to the surface.
• Lava is magma that has reached Earth’s surface.
Lava and ash erupt from a vent, or an opening of
a volcano.
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What are the kinds of volcanic
landforms?
• The location of a volcano and composition of
magma determine the type of volcano.
• Volcanic landforms include shield volcanoes,
cinder cones, composite volcanoes, lava plateaus,
craters, and calderas.
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What are the kinds of volcanic
landforms?
• Volcanic mountains are built from materials
ejected from a volcano.
• The shape and explosiveness of a volcano depend
on the lava’s viscosity, or resistance to flow.
• Pyroclastic material, or hot ash and bits of rock,
may also be ejected into the atmosphere.
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Types of volcanoes:
Depends on the type of explosions
3 types:
1. Shield
Gentle eruptions
Low, broad slopes
2. Cinder Cone
Violent eruptions
Steep slopes
3. Composite
Alternating eruptions
Characteristics of both
Shield volcano
iceland
What are the kinds of volcanic
landforms?
• Shield volcanoes are volcanoes with broad bases
and gently sloping sides.
• They are the result of mild, quiet eruptions made
up of lava, tephra and basaltic rock
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Where do volcanoes form?
• Hot spots are locations far from plate boundaries
where a mantle plume, a column of extremely hot
mantle rock, rises and produces volcanoes.
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What are the kinds of volcanic
landforms?
• Cinder cones are small volcanoes with steep
slopes.
• They form from ash and pieces of solidified lava
that fall around a small vent. They erupt nuees
ardentes- granitic explosions due to trapped
gases, water and slow moving thick silica
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Composite volcanoes:
•Alternating eruptions– most explosive
•Have characteristics of both shield and cinder volcanoes
•They erupt with tephra and lava, and alternate with pyroclastic
flows of lava and gas.
• basaltic and granitic magma, quiet and loud eruptions.
•They generally develop into large, steep mountains.
What are the kinds of volcanic
landforms?
• A volcanic crater is an opening or a depression at
the top of a volcano.
• A crater is caused by eruptions.
• Inside the volcano, molten rock can form an
expanded area of magma called a magma
chamber.
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What are the kinds of volcanic
landforms?
• When the magma chamber empties, the roof of
the chamber can collapse, leaving a large basinshaped depression called a caldera.
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ash
Nuees ardentes
tephra
lahars
Volcanic cinders
Type of eruption determined by:
Type/composition of magma
Basaltic (low silica)  thin, fluid lava  quiet
Granitic (high silica)  thick lava  explosive
Trapped gases
Basaltic  gas escapes easily
Granitic  gases trapped
Water content
Basaltic  low
Granitic  high (water vapor pressure makes it
explosive)
Basaltic lava
Granitic lava
Most recent eruption in N
America: Mt. St. Helen in May
1980
Most Active Volcano:
Kilauea, Hawaii
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tube.com/watch?v=488BkTUsM
a4
Largest Eruption Last Century:
Mt. Pinatubo, Philippians
(Jun1991)
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What are the kinds of volcanic
landforms?
• Fissure eruptions happen when lava flows from
giant cracks, or fissures, in Earth’s surface.
• Because fissures have no central opening, lava
flows out the entire length of the fissure.
• Fissure eruptions produce a flattened layer of
cooled lava called a lava plateau.
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Eruption!
Where do volcanoes form?
• Volcanoes can form at plate boundaries or within
the middle of a plate.
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Where do volcanoes form?
• At divergent plate boundaries, where two plates
are moving away from each other, fissure
eruptions and shield volcanoes are likely to occur.
• ex: Iceland
• At hot spots, which are far from any plate
boundaries, shield volcanoes, fissure eruptions,
and cinder cones can occur.
• ex: Hawaii
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Where do volcanoes form?
• At convergent plate boundaries, composite
volcanoes can occur. ex: Cascade Range
• ex: Cascade Range
:
• Composite volcanoes produce the most violent
eruptions.
• The Ring of Fire is a name for the numerous
explosive volcanoes that form on convergent plate
boundaries surrounding the Pacific Ocean.
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Cascade range
Mayan volcano
Where do volcanoes form?
• Most divergent boundaries are on the ocean floor.
When eruptions occur in these areas, undersea
volcanoes develop.
• These volcanoes and other processes lead to the
formation of a long, underwater mountain range
known as a mid-ocean ridge.
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Where do volcanoes form?
• Magma at convergent boundaries has a high
concentration of fluids, which form gas bubbles.
• Because the magma has a high viscosity, the
bubbles cannot escape easily. As the bubbles
expand, the magma rises faster.
• Eventually, the magma erupts explosively, forming
composite volcanoes or calderas.
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• Chains of volcanoes can form over time as a
tectonic plate moves over a mantle plume.
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Living Near a Volcano
• Many people around the world live near a volcano
because the surrounding soils are fertile for
growing a variety of crops.
• Volcanic rocks can be used in making jewelry,
concrete, water filtration systems, and other
applications.
• However, an eruption can produce destructive
earthquakes, fire, ash, and lava flows, destroying
property and taking lives.
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