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.

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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.

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•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?