DRIFTING CONTINENTS: Plate Tectonics

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Chapter Outline

12.1

Continental Drift: Wegener’s Theory
12.2

Plate Tectonics: An Ocean of Evidence
12.3

Plate Boundary Landforms
12.4

Hot Spots, Folding and Faulting, and Mountain Building
12.5

Geographic Perspectives: The Tibetan Plateau, Climate, and People

Mount Assiniboine stands behind Sunburst Peak on the border of British Columbia and Alberta, Canada. The crust that forms these mountains was transported across the Pacific Ocean, then piled in crumpled heaps along the western edge of the continent.

(© Design Pics Inc./Alamy)

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LIVING PHYSICAL GEOGRAPHY

Why do the coastlines of Africa and South America fit together?
How can whole continents move?
Is it true that Los Angeles will someday be connected to San Francisco?
How do mountains form?

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THE BIG PICTURE

The movements of lithospheric plates create mountains, ocean basins, and many other physical features of Earth. The Tibetan Plateau and its surrounding mountains provide food security.

LEARNING GOALS

After reading this chapter, you will be able to:

12.1

Compare the theory of continental drift with the theory of plate tectonics.
12.2

Describe the evidence used to develop the theory of plate tectonics and explain how lithospheric plates move.
12.3

Describe the three types of plate boundaries and the landforms resulting from each plate boundary type.
12.4

Describe landforms that result from tectonic processes away from plate boundaries.
12.5

Assess the relationship between food security in South Asia and the changing climate of the Tibetan Plateau.

THE HUMAN SPHERE:

Life on Earth’s Shifting Crust

FOR BETTER OR FOR WORSE, HUMANS ARE AFFECTED by the movements of Earth’s lithospheric plates. For instance, earthquakes, which are a result of plate movement, range from minor annoyances to major disasters. Large earthquakes can reduce cities to rubble and generate enormous ocean waves, called tsunamis, that destroy coastal areas (see The Human Sphere in Chapter 14).

Moving plates also create volcanoes, which can be just as disruptive to the lives of people. In April and May of 2010, the eruption of Eyjafjallajökull volcano in Iceland caused the cancellation of some 100,000 airline flights. The next year, in 2011, Grímsvötn, another Icelandic volcano (Figure 12.1), grounded thousands more flights.

Figure 12.1

Volcanic ash from Grímsvötn. On May 22, 2011, Grímsvötn sent plumes of ash into the air that traveled over northern Europe, causing the cancellation of thousands of flights. Aircraft engines fail when they take in volcanic ash, so planes must be grounded until the ash clears.

The movements of Earth’s lithospheric plates are also beneficial to people. Ash from erupting volcanoes, for example, settles to the ground and creates some of the world’s most fertile agricultural soils, called andisols (see Section 9.1). The moving plates also build the land on which we live. The land surface of many island nations, such as Japan, Indonesia, and much of New Zealand, was built by volcanoes. Plate movements even modify the chemistry of the atmosphere and its greenhouse effect by moving carbon from the atmosphere to the lithosphere and back again over millions of years (see Section 11.4).

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This chapter explores Earth’s dynamic lithosphere, first in the context of continental drift theory, then in the modern framework of plate tectonics theory. Next, it describes interactions between plates and the resulting topography. Finally, it explores the Tibetan Plateau’s affect on climate and people.