ch. 18 sec. 1 - mr. geraghty's blog · 2018-10-11 · 1. oceanic-continental subduction zone...
TRANSCRIPT
Ch. 22.6
Volcanoes
Review Vocabulary
convergent: tending to move
toward one point or to
approach each other
The locations of volcanoes are
mostly determined by plate
tectonics.
IntroVolcanoes348
Volcanism describes all the processes
associated with the discharge of
magma, hot fluids, and gases.
I. Zones of Volcanism
Most volcanoes form at plate boundaries.
The majority form at convergent
boundaries and divergent boundaries.
Fig. 18.1 pg. 500
1. Oceanic-continental subduction zone
2. Denser oceanic plate subducts
a. Parts of the plate melt
b. Magma rises
A. Convergent volcanism
3. Characterized by explosive eruptions
Mt. St. Helens
Volcanoes
Section 18.1
a. Circum-Pacific Belt (AKA the Pacific
Ring of Fire)
b. Mediterranean Belt (between the
Eurasian, African, and Arabian
plates)
4. Two major belts
Where are most of Earth’s active
volcanoes?
A. Circum-Pacific belt
B. East African Rift
C. Mediterranean Belt
D. Cascade Range
A. B. C. D.
0% 0%0%0%
ring45fire
1. Nonexplosive eruptions
2. Pillow lava
3. Approximately 2/3 of all volcanoes
B. Divergent volcanism
Divergent Plate
Boundaries
About two-thirds of Earth’s
volcanism occurs along
convergent boundaries.
A.True
B.False
A. B.
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Volcanic belts form along
A. islands in the Pacific
Ocean.
B. North American
mountain ranges.
C. the boundaries of Earth’s
plates.
D. the coast of Antarctica. A. B. C. D.
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Where do volcanic eruptions tend
to be nonexplosive?
A.over hot spots
B.at divergent
boundaries
C.in the upper mantle
D.at convergent
boundaries A. B. C. D.
0% 0%0%0%
•far from plate boundaries
•high-temperature plumes of
mantle material rise toward
the surface
C. Hot spots - hot area in Earth’s mantle
1. Volcanoes
a. Hawaiian islands
b. Magma plume remained
stationary
c. Pacific Plate slowly moved
northwest
The volcanoes on the
oldest Hawaiian island,
Kauai, are inactive
because the island no
longer sits above the
stationary hot spot. The
world’s most active
volcano, Kilauea, on the
Big Island of Hawaii, is
currently located over
the hot spot.
Chains of volcanoes
that form over
stationary hot spots
provide information
about plate motions.
The rate and
direction of plate
motion can be
calculated from the
positions of these
volcanoes.
Loihi – another
volcano is forming on
the seafloor southwest
of the big island
2. Plate Motion
The Hawaiian
islands are at one
end of the
Hawaiian-Emperor
volcanic chain. The
oldest seamount,
Meiji, is at the other
end of the chain and
is about 80 million
years old.
141hawaii
3. Flood basalts – continental hot spots
a. lava flows out of long cracks
b. fissures
The Columbia River basalts,
located in the northwestern
United States, were formed this
way.
c. Lava plateaus
i. Thin, runny lava
ii. great distances before cooling
About 65 mya in India, a huge flood
basalt eruption created an enormous
plateau called the Deccan Traps. The
volume of basalt in the Deccan Traps is
estimated to be about 512,000 km3.
Hypothesis – may have
caused a global climate
change that influenced
the extinction of the
dinosaurs.
The formation of the Hawaiian
islands is one example of
A. volcanoes forming
over a hot spot.
B. volcanoes forming
along plate
boundaries.
C. the Ring of Fire.
D. continental drift. A. B. C. D.
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Where is the world’s most active
volcano?
A. Mexico
B. Italy
C. Alaska
D. Hawaii
A. B. C. D.
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Volcanism What kind of volcanism is shown
in the figure below?
a. divergent
b. convergent
c. hot spot
d. flood basalt
1 2 3 4
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III. Anatomy of a Volcano
A. Lava reaches the surface by traveling
through a tubelike structure called a
conduit.
B. The lava then emerges through an opening
called a vent.
C. Magma Chamber
D. Bowl-shaped depression called
a crater
E. Larger depressions, called
calderas, can be up to 50 km
in diameter.
1. Hole left by
volcanic collapse
2. Main vent
empties
Volcanoes
Section 18.1
Caldera Formation
A.lava plateau
B.caldera.
C.cinder cone.
D.shield volcano.
A. B. C. D.
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The huge hole left by the collapse
of a volcanic mountain is called a
III. Types of Volcanoes
The appearance of a volcano
depends on two factors:
type of material
type of eruptions
A. Shield volcanoes
1. Thin lava from vent
2. Gently sloping mountain
3. Quiet eruptions
B. Cinder cone
1. Ash, cinders, & bombs (tephra)
2. Explosive eruptions
C. Composite volcanoes
1. Lava flows & explosive
eruptions
2. Alternate layers of lava
and ash
Volcanism Which type of volcano usually
produces the most violent
eruptions?
A. Shield
B. Underwater
C. Cinder cone
D. Composite A. B. C. D.
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When ash, cinders, and bombs
build up in a steep pile around a
volcano’s vent, the result is a
A.cinder cone volcano
B.shield volcano.
C.composite volcano.
D.dormant volcano. A. B. C. D.
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Table 18-1 Page 506
The locations of volcanoes are
mostly determined by plate tectonics.
Volcanism includes all the processes in
which magma and gases rise to Earth’s
surface.
Most volcanoes on land are part of two
major volcanic chains: the Circum-Pacific
Belt and the Mediterranean Belt.
Parts of a volcano include a vent,
magma chamber, crater, and
caldera.
Flood basalts form when lava
flows from fissures to form flat
plains or plateaus.
There are three major types of
volcanoes: shield, composite, and
cinder cone.
Answer: A caldera is a large depression that forms after the
magma chamber under a volcano empties. The sides and top of the volcano collapse into the empty chamber, leaving a large circular
depression.
Volcanism
What is a caldera?