Understanding Volcanoes: it's types and forms

This PowerPoint presentation explains volcano formation, types, and eruption processes. It covers causes like plate movements, famous volcanoes, and their effects on the environment and humans. Visuals, diagrams, and real examples make it engaging and informative for students and learners.

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Section 1 Volcanic Eruptions
Bellringer
Make a labeled drawing showing what happens
when a volcano erupts. Then describe the
photographs on pages 156 and 157 in your
textbook. Why do the characteristics of volcanic
eruptions vary?
 
Illustrate your responses in your science journal.
Chapter F6

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Section 1 Volcanic Eruptions
Describe the different types of volcanoes and how
they affect Earth’s surface.
Objectives
Chapter F6

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Agenda
•Today we will:
–Complete a do now.
–Learn about volcanoes by teacher power point.

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Vocabulary
•shield volcano
•cinder cone volcano
•composite volcano

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Section 1 Volcanic Eruptions
Volcanic Eruptions
• A volcano is a vent or fissure in the Earth’s
surface through which molten rock and gases are
expelled.
• Molten rock is called magma.
• Magma that flows onto the Earth’s surface is
called lava.
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Section 1 Volcanic Eruptions
Nonexplosive Eruptions
• Nonexplosive eruptions are the most common type
of volcanic eruptions. These eruptions produce
relatively calm flows of lava in huge amounts.
• Vast areas of the Earth’s surface, including much
of the sea floor and the Northwestern United States,
are covered with lava form nonexplosive eruptions.
Chapter F6

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Section 1 Volcanic Eruptions
Explosive Eruptions
• While explosive eruptions are much rarer than non-
explosive eruptions, the effects can be incredibly
destructive.
• During an explosive eruption, clouds of hot debris,
ash, and gas rapidly shoot out from a volcano.
• An explosive eruption can also blast millions of tons
of lava and rock from a volcano, and can demolish
and entire mountainside.
Chapter F6

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Section 1 Volcanic Eruptions
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Volcanic Eruptions and Climate Change
• During a large-scale volcanic eruption, enormous
amounts of volcanic ash and gases are ejected into
the upper atmosphere.
• As volcanic ash and gases spread throughout the
atmosphere, they can block enough sunlight to
cause global temperature to drop.
• Other effects of volcanic eruptions are shown in the
following Visual Concepts presentation.
Section 2 Effects of Volcanic Eruptions
Chapter F6

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Effects of Volcanoes on Earth
Section 2 Effects of Volcanic Eruptions
Click below to watch the Visual Concept.
You may stop the video at any time by pressing
the Esc key.
Visual Concept
Chapter F6

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Different Types of Volcanoes
• Volcanic eruptions can cause profound changes in
climate, but the changes to the Earth’s surface are
more familiar.
• Perhaps the best known of all volcanic landforms
are the volcanoes themselves.
Section 2 Effects of Volcanic Eruptions
Chapter F6

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Different Types of Volcanoes, continued
There are three basic types of volcanoes:
• Shield Volcanoes
• Cinder Cone Volcanoes
• Composite Volcanoes
Section 2 Effects of Volcanic Eruptions
Chapter F6

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Section 2 Effects of Volcanic Eruptions
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Different Types of Volcanoes, continued
• Shield volcanoes are built of layers of lava that
are released from repeated nonexplosive eruptions.
The lava spreads out over a wide area, creating a
volcano with gently sloping sides.
Section 2 Effects of Volcanic Eruptions
Chapter F6

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Different Types of Volcanoes, continued
• Cinder cone volcanoes are made of pyroclastic
material usually produced from moderately explosive
eruptions. The pyroclastic material forms steep
slopes.
Section 2 Effects of Volcanic Eruptions
Chapter F6

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Different Types of Volcanoes, continued
• Composite volcanoes are formed from explosive
eruptions of pyroclastic material, followed by quieter
flows of lava. These formations, among the most
common types of volcanoes, have broad bases and
sides that get steeper toward the top.
Section 2 Effects of Volcanic Eruptions
Chapter F6

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Other Types of Volcanic Landforms
• In addition to volcanoes, there are other landforms
produced by volcanic activity.
• Craters are funnel-shaped pits near the top of the
central vent of a volcano.
Section 2 Effects of Volcanic Eruptions
Chapter F6

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Other Volcanic Landforms, continued
• Calderas are large, semicircular depressions that
form when the magma chamber below a volcano
partially empties and causes the ground above to
sink.
• Calderas can appear similar to craters, but are
many times larger.
Section 2 Effects of Volcanic Eruptions
Chapter F6

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Section 2 Effects of Volcanic Eruptions
Chapter F6

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Other Volcanic Landforms, continued
• Lava Plateaus are wide, flat landforms that result
form repeated nonexplosive eruptions of lava that
spread of a large area.
• The lava that formed lava plateaus usually erupted
from long cracks, or rifts, in the crust over a period of
millions of years.
Section 2 Effects of Volcanic Eruptions
Chapter F6

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Section 3 Causes of Volcanic Eruptions
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When Tectonic Plates Separate
• At a divergent boundary, tectonic plates move
away from each other, forming a set of deep cracks
called a rift zone between the plates.
• Mantle rock rises to fill the gap opened by the
separating tectonic plates. When mantle rock nears
the surface, pressure decreases, which causes the
mantle rock to melt and form magma.
Section 3 Causes of Volcanic Eruptions
Chapter F6

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Section 3 Causes of Volcanic Eruptions
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When Tectonic Plates Separate, continued
• Mid-Ocean Ridges Form at Divergent Boundaries
Lava that flows from undersea rift zones produces
volcanoes and mountain chains called mid-ocean
ridges.
• At these mid-ocean ridges, lava flows out and creates
new crust. Most volcanic activity on Earth occurs at
mid-ocean ridges.
Section 3 Causes of Volcanic Eruptions
Chapter F6

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When Tectonic Plates Collide
• Convergent boundaries are places where tectonic
plates collide.
• When an oceanic plate collides with a continental
plate, the oceanic plate usually slides underneath
the continental plate. This is a process called
subduction.
Section 3 Causes of Volcanic Eruptions
Chapter F6

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When Tectonic Plates Collide, continued
• Subduction Produces Magma As descending
oceanic crust scrapes past the continental crust,
the temperature and pressure increase.
• The following Visual Concepts presentation shows
how subduction produces magma, and how that
magma can rise to form a volcano.
Section 3 Causes of Volcanic Eruptions
Chapter F6

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Volcano Formation at Convergent Boundaries
Section 3 Causes of Volcanic Eruptions
Click below to watch the Visual Concept.
You may stop the video at any time by pressing
the Esc key.
Visual Concept
Chapter F6

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Hot Spots, continued
• A hot spot often produces a chain of volcanoes.
One theory is that the mantle plume stays in the
same spot while the tectonic plates move over it.
• Other scientists think that hot spots are the result
of cracks in the Earth’s crust.
• The theory argues that hot-spot volcanoes occur
in chains because they form along the cracks in the
Earth’s crust.
Section 3 Causes of Volcanic Eruptions
Chapter F6

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Predicting Volcanic Eruptions
Volcanoes are classified in three categories:
• Active Volcanoes
• Dormant Volcanoes
• Extinct Volcanoes
Section 3 Causes of Volcanic Eruptions
Chapter F6

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Active, Dormant, and Extinct Volcanoes
Section 3 Causes of Volcanic Eruptions
Click below to watch the Visual Concept.
You may stop the video at any time by pressing
the Esc key.
Visual Concept
Chapter F6

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Homework
•Handout.