Erosion occurs in many ways as stated above. It usually takes many years for erosion to be noticed, such is the case with the Grand Canyon. But it is common to see erosion take place in a quick fashion. An example would be the recent erosion along the California coastline. May homes and a great deal of land has eroded into the Pacific due to intense wave action and weak soil/bedrock compositions. However, California will not just fall into the ocean because of erosion. The amount of land being lost is very small compared to the total land mass.

Factors Affecting Transportation of Sediments
Running water is the primary agent of erosion on Earth. Most running water is found in streams and rivers. There are many factors that affect the movement of sediments in a stream.

Gradient (slope), discharge, and channel shape influence a stream’s velocity and the erosion and deposition of sediments. Sediments carried by a stream are almost always rounded due to the grinding action of the water on the rocks, a process called abrasion. Streams are usually formed in V-shaped valleys; and deltas, flood plains, and meanders are results of what a stream can form. The watershed of a stream is the area drained by a stream and its tributaries (smaller feeder streams).

The average velocity (speed) of a stream depends on its slope and discharge, which in turn can explain the carrying power of a stream. As the velocity of the stream water increases, the size of the particles carried in the stream also increases, a direct relationship.

Streams carry materials in 4 distinct ways:

Floatation, solution (dissolved particles), suspension (within the water profile), and bed load (bouncing and dragging along the stream bed. See the graph below from page 6 of  the Earth Science Reference Tables to explain particle size to stream speed.

Meanders are another very important part of stream erosion. In a meandering stream velocity is lowest (High Potential Energy) along the inner banks because it is there that water encounters the most friction, and therefore the flow is reduced. Along a straight channel segment, water moves the fastest in mid-channel, near the surface. But as water moves around a bend, the zone of high velocity (High Kinetic Energy) swings to the outside of the channel. As water rushes past the outer part of the bend, sediment is continuously eroded from the riverbank and is swept downstream. With the slower flow concentrated around the inner side of each bend, coarse sediment accumulates. Thus, a meandering pattern is created along the course of the river, with shallow water and on the inside bends and steep banks on the outside.

Since the material lining the banks does not remain uniform the entire length of a river system, another landform -- an oxbow lake -- can develop. If river water runs into resistant sediments, the movement of the meander can slow downstream. As other meanders continue to migrate through softer sediments upstream, they eventually intersect the slower-moving meander and cut off the channel between the two, forming an independent loop that will become a lake (see below).

Adapted from original illustration by Steven Fick, Canadian Geographic, July/Aug '93

Valleys Eroded by Streams and Glaciers
Valleys that have been eroded by streams are v-shaped, while valleys that have been eroded by glaciers are u-shaped.

Effect of Humans on Erosion
Humans add greatly to the natural processes of land erosion through activities, such as highway and construction, destruction of forests (clear-cutting), set forest fires, poor landfill projects, etc… Today, human activities contribute more than ever to the erosion on the Earth’s surface.