River Processes

Question 1

What is corrasion/abrasion?

Answer 1

• It is the process of materials being picked up and being rubbed against the bank and beds of the river by abrasion.
• It is most effective during floods.
• If there are hollows in the river bed pebbles will become trapped, and their turbulent eddies swirl pebbles around to form potholes.

Question 2

What is Attrition?

Answer 2

Attrition is the process of bed load/materials being moved downstream, and colliding with boulders. The impact may break the rock into smaller pieces.

Question 3

What is Hydraulic Action?

Answer 3

• The sheer force of the water as the turbulent current hits river banks pushes water into cracks.
• Air in the cracks is compressed; over time pressure is increased and eventually the bank will collapse.

Question 4

What is solution/corrosion?

Answer 4

When the water has a concentration of carbonic or humic acid. It is free of discharge or volume and is to do with the chemical composition of the river. It causes certain rocks to dissolve, like limestone, and is then carried downstream in solution.

Question 5

What is suspension?

Answer 5

• Very fine particles of clay and silt are dislodged and carried by turbulence in a fast flowing river.
• the greater the velocity=the larger the quantity and size of load that can be picked up.

Question 6

What is solution?

Answer 6

water flowing in the river contains acids. If the bedrock is ready soluble it is constantly dissolved in the running water and removed in solution.

Question 7

What is Bedload transportation? Name the two types.

Answer 7

• Saltation: this occurs when pebbles, sand and gravel are temporarily lifted by the current and bounced along the bed in a hopping motion.
• Traction: This occurs when the largest cobbles and boulders roll or slide along the bed. The largest can only be moved in exreme floods.