Back to Lecture Menu

NORTH AMERICA

Great Plains

The Great Plains of North America extend east from the Rocky Mountains and run north-south all the way through the United States and through most of Canada. The Great Plains can be subdivided into the Low Plains and the High Plains. The High Plains are in the western half (a long, narrow strip, nearest the mountains) and the Low Plains are in the eastern half (a long, narrow strip, nearest the Mississippi River in the U.S. and approaching Hudson Bay in Canada). The Great Plains are subdivided into Low and High Plains based on their elevations. Many areas of the High Plains are 4000 to 5000 feet in elevation. Most of the Low Plains are closer to 1000 feet in elavation or less. If you have ever seen the Clint Eastwood movie entitled "High Plains Drifter", it is based in the High Plains of North America.

The important item to remember about the Great Plains is that the High Plains are drier than the Low Plains. Therefore, short grasses grow in the semi-arid High Plains while tall grasses grow in the more humid Low Plains. Because of this difference in moisture (as you should expect), less agriculture takes place in the High Plains when compared to the Low Plains. (However, some of the most sophisticated irrigation equipment in the world allows some farmers to grow crops in the High Plains.) The most dominant land use in the High Plains is open pasture for cattle. The High Plains of North America is the cattle capitol of the world.

But wait a minute. Why are the Low Plains more humid than the High plains? The predominant winds blow from west to east in North America. And there is no moisture to be picked up in the Great Plains. Why are the eastern Low Plains wetter than the western High Plains?

Answer: the Gulf of Mexico.

The Gulf of Mexico allows warm moist air to move far into the interior of the continent-- up the Mississippi River Valley and beyond. And remember, the Great Plains are relatively flat and treeless all the way from Texas to the Arctic Circle. There is nothing in the way of this warm moist air moving in from the Gulf of Mexico. This is why the eastern Low Plains are more moist than the western High Plains.

And when a mass of warm moist air from the Gulf runs into a mass of cold dry air from Canada, a line of (often) violent thunderstorms forms and provides needed precipitation.

Russia doesn't have a "Gulf of Mexico" to help warm it and provide moisture. North America is at a real agricultural advantage over many areas of the world due to its physical geography.

You have successfully completed the physical geography portion of the lecture.

Back to Lecture Menu

or

Advance to Human Geography