Students know some changes in the earth are due to slow processes, such as erosion, and some changes are due to rapid processes, such as landslides, volcanoes, and earthquakes.

When a landslide, volcano, or earthquake happens, the event can be very fast, especially compared with a slow erosion process happening over thousands of years. However, one complication to this apparently simple standard is that the underlying basis of the landslide, volcano, or earthquake is very likely to be a slow process. Earth’s tectonic plates move at the rate that a fingernail grows, about one centimeter per year. We would normally call this a slow process. Nothing very much seems to happen for hundreds of years as two plates slide past each other. Then suddenly they jolt several feet and we experience the sudden earthquake. A more sophisticated understanding of this standard involves the realization that rapid events can be due to underlying slow processes.