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North America

Modern Geologic Events In North America

California lies between two different kinds of plate boundaries. To the south, the crust under California is growing; to the north it is shrinking. The part of California that sits on the Pacific plate between these two forces is moved northward in sudden increments of a few feet which are felt as earthquakes. A few feet at a time, in earthquakes that happen every few decades, the part of California west of the San Andreas Fault will move northward along the coast.

Active faults also exist elsewhere in the United States, in the midwest and in South Carolina. The last sizeable earthquakes in these regions occurred more than a hundred years ago, and geologists assume that earthquakes will probably occur within the next hundred years. The Pacific Northwest and Alaska, sitting atop active tectonic environments, will certainly be shaken by earthquakes for millions of years to come. The Great Basin, the western Rocky Mountains, and the United States northeast are all considered tectonically active enough for earthquakes to be considered possible.

North America's volcanic mountain ranges, the Cascades, and the relatively recent Mexican volcanic belt, have erupted often in the recent geologic past. These mountains will certainly continue to erupt in the near geologic future.

Resources

Books

Colbert, E., ed. Our Continent. Washington, DC: The National Geographic Society, 1976.

Hancock, P. L., and B. J. Skinner, eds. The Oxford Companion to the Earth. Oxford: Oxford University Press, 2000.

Harris, D., and E. Kiver. The Geologic Story of the National Parks and Monuments. 4th ed. New York: John Wiley and Sons, 1985.

Menzies, Gavin. 1421: The Year China Discovered America. New York: William Morrow & Co., 2003.

Stetter, J., ed. Geology of the Great Basin. University of Nevada Press, 1986.

Sullivan, W. Landprints. New York: The New York Times Book Co. Inc., 1984.


Periodicals

Bokelmann, G.H.R. "Which Forces Drive North America?" Geology 30, no. 11 (2002): 1027-1030.


Clinton Crowley

KEY TERMS


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Archean eon

—The interval of geologic time from 3.8 billion years ago to 2.5 billion years ago.

Canadian shield

—The oldest part of North America, made of rocks formed between 3.8 and 2.5 billion years ago, that underlies much of northern and eastern Canada.

Collisional mountain belt

—A mountain range, like the Appalachians, caused by one continent running into another continent.

Continental arc

—A volcanic mountain range, like the Cascades, that forms on the tectonically active edge of a continent, over a subduction zone.

Craton

—A piece of a continent that has remained intact since Earth's earliest history, and which functions as a foundation, or basement, for more recent pieces of a continent.

Fault block mountains

—A mountain range, like the Front Range of the Rocky Mountains, caused by horizontal forces that squeeze a continent, fracturing its crust and pushing blocks of crust up to form mountains. Also, a mountain range, like the Shoshone Range of Nevada, caused by horizontal forces that stretch a continent, fracturing the crust and causing some blocks of crust to sink down, leaving other blocks standing at high elevations above the valleys.

Glacial till

—Rocks, soil and other sediments transported by a glacier then deposited along its line of farthest advance.

Island arc

—A volcanic mountain range, like the Aleutians, built on a tectonically active plate boundary in the sea, which appears as islands.

Phanerozoic eon

—The interval of geologic time beginning 570 million years ago, the rocks of which contain an abundant record of fossilized life.

Plate tectonics

—The interactions of the plates of Earth's crust, which float on top of Earth's mantle, and whose movements through geologic time have caused the major features of the continents.

Precambrian era

—The combined Archean and Proterozoic eons, the first four billion years of Earth's history.

Proterozoic eon

—The interval of geologic time beginning 2.5 billion years ago and ending 570 million years ago.

Additional topics

Science EncyclopediaScience & Philosophy: Nicotinamide adenine dinucleotide phosphate (NADP) to Ockham's razorNorth America - North America In The Proterozoic Eon, Phanerozoic Time, Eastern And Southern Borders Of North America - Geologic history