Gullies are being formed. The earth's surface is changing all the time. Water, wind, and ice are constantly at work, wearing away and building up the land. Some changes take place in a very short time. Floods can change the course of a river in a few days.
Dust storms can carry huge amounts of soil away very rapidly.
However, most of the big changes in the earth's surface take thousands of years. At various times, the earth is exposed to along periods of extreme cold followed by periods of intense heat. Parts of the land we see now were once under water and land forms that were once above water are now deep under the water. In most cases the changes are so gradual we cannot detect them in the span of a lifetime. Today we want to learn how our weather has built up or worn down the earth's surface to form mountains, valleys, deserts, plains, soil, lakes, and rivers.