Physical Geography:
Plate Tectonics

• Historical Perspective
• Why do we care?
• Why There? - Boundaries

An understanding of the theory of plate tectonics is useful to understand the world's basic physical geography. Remember that geographers study not only location (where?), but also why there? and why do we care? As you go through this exercise you should not only learn the LOCATIONS of the world's continents, mountain chains, ocean trenches, earthquakes, and volcanoes, but also WHY they are there. Furthermore, we should think about "WHY DO WE CARE?"

[Most of the information in this exercise came from a U. S. government publication which can be found at: http://pubs.usgs.gov/publications/text/dynamic.html]

Historical Perspective: The Theory of Plate Tectonics

Every semester I encounter students who strongly question the theory of plate tectonics. Questioning is good, but this theory is very well accepted because it explains so much. It has become the foundation of the disciplines of geology and physical geography. Just like the theory of evolution forms the foundation of the study of biology.

Quickly skim the history of the theory of plate tectonics found at: http://pubs.usgs.gov/publications/text/historical.html

Evidence

There is much evidence for the theory of plate tectonics. See http://pubs.usgs.gov/publications/text/developing.html to get an idea why this revolutionary theory is accepted today.

A summary of the evidence supporting the theory of plate tectonics would include:

• The "fit" of continents
• fossil evidence
• ocean ridges
• magnetic stripping
• sea floor spreading
• earthquakes

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Why do we care?

Plate tectonics helps explain the location of the world's basic physical features like the location of continents, mountain chains, and ocean trenches. Also the theory can be used to explain the location of natural hazards like earthquakes (see: http://geography.about.com/library/weekly/aa122297.htm), volcanoes, and tsunamis (tidal waves). Furthermore, the location of many of the earth's natural resources like fertile soils, ore deposits, fossil fuels, and geothermal energy can be explained by the theory of plate tectonics.

The following site gives a more in-depth explanation of how the theory explains the location of these important natural hazards and resources. I suggest that you quickly skim the site, but careful reading and note-taking is not necessary.

• http://pubs.usgs.gov/publications/text/tectonics.html#anchor19989073

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Why There? - Boundaries

I do want you to have a deeper understanding of how plate tectonics helps explain the location of the world's basic physical features like the location of continents, mountain chains, and ocean trenches, as well as volcanoes and earthquakes. Most of these significant physical features occur at the boundaries of the world's crustal plates. There are four types of plate boundaries [Boundaries]:

• Divergent boundaries -- where new crust is generated as the plates pull away from each other. Divergent boundaries explain the volcanoes of Iceland [Iceland] and the rift valleys (deep 60 mile wide trenches) of eastern Africa [Africa Escarp].
• Convergent boundaries -- where crust is destroyed as one plate dives under another. convergent boundaries explain the location of the world's ocean trenches, some mountain chains like the Andes of South America and the Himalayas of Asia [India], and the location of most of the world's volcanoes [ringfire].
• Transform boundaries -- where crust is neither produced nor destroyed as the plates slide horizontally past each other. Transform boundaries explain the locations of many of the world's earthquakes. [Calif] [worquake]
• Plate boundary zones -- broad belts in which boundaries are not well defined and the effects of plate interaction are unclear.

A more detailed explanation of how these plate boundaries create such physical features can be found at http://pubs.usgs.gov/publications/text/understanding.html#anchor6715825.

OPTIONAL

• http://www.scotese.com/
• http://www.scotese.com/pangeanim.htm

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