EROSION AND DEPOSITION

Runoff and Erosion  Precipitation over the United States averages about 75 cm per year. About 22.5 cm becomes runoff. Generally, more runoff means more erosion.

Runoff and Erosion  Water flowing across the land runs together to form rills, gullies, and streams.

Erosion by Rivers  A waterfall forms where a flat layer of tough rock lies over a layer of softer rock that erodes easily. When the softer rock erodes, pieces of the harder rock above break off, creating the waterfall’s sharp drop.

Erosion by Rivers  Erosion often forms meanders and oxbow lakes where a river winds across its floodplain.

Deposits by Rivers  Deposition creates landforms such as alluvial fans and deltas.

The Course of a River  The slope and size of a river, as well as the sediment it carries, determine how a river shapes the land.

Groundwater Erosion  Karst topography is found in many parts of the United States where the bedrock is made up of thick layers of limestone.

Groundwater Erosion  Chemical weathering of limestone and groundwater erosion can create a limestone cave.