As part of an effort to understand why the Earth has become progressively cooler over the last 50 million years, Professor Whipple and colleagues at MIT are studying how relief, or the differences in height between peaks and valleys, changes in response to a change in climate. The peaks and valleys of the Earth's surface are caused by the giant tectonic plates of the Earth's crust crashing into each other and the continually wearing forces of weather, water and glacial ice. These uneven surfaces, in turn, cause changes in weather patterns. Although it seems that erosion would cause mountains to get shorter, it can in some circumstances actually lead to uplift of mountain peaks. Because the low-density crust of the Earth floats on the mantle like an ice cube on water, the mean elevation of mountain ranges is set by crustal thickness, just as larger ice cubes protrude farther above the surface.
Erosion thins the crust and generally reduces mean elevation.
However, if erosion increases relief, then mountain peaks tend to rise as valleys deepen. Professor Whipple does not argue with the theory that Cenozoic climate change has enhanced erosion rates. The trick is that you can't separate what happens in the channel from what happens at the ridge top. If the main valley is lowered by rapid incision, the tributary valleys and the hillslopes will follow, he said. This results in an overall decrease in relief.