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Laboratory Manual for Introductory Geology 4e

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EXERCISE 2.13

Why Are There More Earthquakes and Volcanoes on One Side of Some Continents

Than on the Other Side?

Name:

Course:

Section:

Date:

(a) Are all continental coastlines plate boundaries? Explain.

(b) Label active continental margins with a red A on the following diagram, and passive margins with a blue P.

Two have been identified to help you get started.

The Earth’s major lithosphere plates.

Trench or

collision zone

Ridge

Transform

boundary

Eurasian Plate

Juan

de Fuca

Plate

Passive

Margin

African

Plate

Iran

Plate

Arabian

Plate

Philippine

Plate

Australian-

Indian Plate

Bismarck

Plate

Pacific

Plate

Cocos

Plate

North

American

Plate

Nazca

Plate

A

P

Caribbean

Plate

Active

Margin

Mid-

Atlantic

Ridge

South

American

Plate

African

Plate

Plate

Interior

Antarctic

Plate

Plate

Boundary

Antarctic

Plate

Scotia Plate

Now look in more detail at the east and west coasts of South

America in the enlarged bathymetric and topographic map to

the right.

Map of the South Atlantic Ocean floor and adjacent

continents.

(c) How far is the easternmost point in South America from the

nearest plate boundary?

What

kind of boundary is it?

(d) How far is the westernmost point in South America from the

nearest plate boundary?

What

kind of boundary is it?

(e) Which coast of South America would you expect to have

the most frequent earthquakes?

Volcanic activity?

Explain.

Mid-Atlantic Ridge

1,000 km

2.6 ACTIVE VERSUS PASSIVE CONTINENTAL MARGINS

51

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