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In the late 1800s, U.S. geographer and Harvard professor William Morris Davis developed his "cycle of erosion" theory, holding that features like valleys and plains were shaped by physical forces such as water.
His theory was groundbreaking but not completely accurate. Still, the idea sparked the modern science of geomorphology, or the study of Earth's landforms.
Sometimes called "the father of American geography," Davis strongly believed that geography should be taught not only at the college level but in grade school and high school too. He also taught many of the important geographers who followed him, including Ellsworth Huntington, who studied the relationship between climate and civilization.
At a time when people mainly believed that landforms like mountains and valleys had been created by the biblical great flood, Davis was one of a few people who thought other forces were at work. So he focused his study on how rivers created landforms. He called his theory the "geographical cycle," and it basically went like this:
* First, mountains are "uplifted," or pushed upward by a geological force.
* Then, in a stage he called "youth," water flowing through the landscape carves out sharp, steep valleys.
* In the "maturity" stage, the valleys become wider and smoother as time passes.
* The mountains slowly turn into hills and flatten out in the "old age" stage, eventually leaving only a flat surface, or "peneplain," which Davis called the "base level."
* Lastly, "rejuvenation" occurs: Another uplift of mountains takes place, and the cycle starts again.
Despite its flaws -- for example, erosion also takes place during the "uplift" period when mountains are forming -- Davis's theory is still valuable as a basic explanation for how streams develop.
