1	River Erosion Geoscience 1 Lancaster High School Mr. Hayhurst
2	Erosion Erosion is the removal of soil, sediment, regolith and rock fragments from the landscape. Erosion is responsible for alterations of nature that leave hills and valleys.
3	Erosion Three process of erosion are: Detachment Entrainment Transport Erosion requires a medium whereby the debris can be carried away from its origin.
4	Detachment Detachment is the separation of a material from its surrounding material. The amount of energy required to complete the separation will be dependant upon the bonds that hold the material together. Examples of detachment are plucking, cavitation, raindrop impact, and abrasion.
5	Plucking Plucking is similar to the way potholes in roads are created. Water freezes and expands which breaks apart the bonds that hold the road together. Also known as frost wedging.
6	Cavitation Cavitation is caused by implosion of air bubbles which causes a jet of high pressure and high speed water to shoot forth causing enough stress to break down the bonds of the material it strikes.
7	Raindrop Impact The force of falling raindrops supply enough energy to break down the bonds of any material that it strikes.
8	Abrasion Particles that are carried in the transporting medium (water or wind) act as a grinding agent on the materials with which they collide.
9	Entrainment Entrainment is the lifting of the eroded particle away from its surroundings by the cause of erosion.
10	Transport Transport is the medium (water or wind) that carries the particle away from its origin.
11	To the Sea… A by-product of a river’s flow to the sea is the erosion of its bank and bedrock. As it does so it creates new landforms such as valleys and gorges along its course. River erosion is the gradual wearing down and removal of rock and soluble material from the river’s bank and bed.
12	Downward Erosion The amount of erosion that the river causes is related to its velocity. Rivers erode downward trying to reach a base level, which is ultimately sea level.
13	Lateral and Vertical Erosion High-gradient streams which have more kinetic energy will down cut (vertical erosion) more rapidly than low gradient streams. The process of down cutting flattens mountains and widens flood plains.
14	Lateral and Vertical Erosion Low Gradient streams with less velocity tend to be wide. They increase the channel width through lateral erosion. Low gradient streams are often braided.
15	Lateral and Vertical Erosion
16	Erosion Processes A river erodes by the processes of corrasion, attrition, solution and hydraulic action. Corrasion (abrasion) is the process whereby the river uses its load as a grinding tool wearing down the materials found in the bed and the bank. This process dislodges materials and carries them away. The process is both vertical and lateral. Corrasion creates potholes in the bed of the river.
17	Erosion Processes Attrition (corrosion) is the process whereby materials that are being carried away collide with materials in the bed and bank. This process tends to pulverize and reduce the material in size and creates silt. The solution process is where the water acts as a solvent. It breaks down and dissolves the soluble materials and then carries them away as ions in solution.
18	Erosion Processes In the hydraulic process the mere force of the moving river breaks down rocks. It removes them from the bed and bank of the river and drags them along with the energy of the river.
19	Results of River Erosion River Erosion results in potholes, plunge pools, rapids, waterfalls, gorges and valleys. Potholes are circular depressions on the river bed formed by corrasion that involves pebbles that are trapped in hollows on the river bed and are swirled about in turbulent water.
20	Results of River Erosion Plunge Pools are large depressions at the foot of a waterfall. They are deepened by the hydraulic action of the plunging water hitting less resistant rocks. Rapids are a series of very short and fast falls that evolve from the alternating erosions of resistant and less resistant rocks.
21	Results of River Erosion Waterfalls are vertical flows of fast moving water that flow downward from great heights. Less resistant rocks are eroded more quickly than higher resistant rocks which alters the gradient.
22	Results of River Erosion Gorges are valleys which are steep sided, deep and narrow. They are brought about by the water eroding the base of the falls especially the soft, less resistant rock layers thereby leaving no support for the top hard rock shelf which then tends to break away. The net effect of erosion is to carve out valleys.
23	Questions What are the four processes by which a river erodes materials? How are potholes created? What is the net effect of river erosion? Why does a high gradient stream down cut (vertical erosion) more rapidly than a low gradient stream?
24	Answers The four processes of erosion that a river demonstrates are: corrasion, attrition, solution and hydraulic. Potholes are formed in the river bed by the swirling about of pebbles on the river bed due to water turbulence.
25	Answers Potholes are formed in the river bed by the swirling about of pebbles on the river bed due to water turbulence. The net effect of river erosion is the creation of valleys.