Explain the formation of a Waterfall
A typical river formation question would be:
Explain the formation of a *.
You may wish to use an annotated diagram in your answer (8)
*The features you can be asked are:
Waterfalls
V-shaped valleys
Meanders
Ox-Bow Lake
Meanders & Oxbow Lakes form in the middle and lower courses, where the valley is wide enough for lateral erosion to occur.
Over time, they become more pronounced and can change the course of rivers.
Digital Workbook and Paper Jotter
Draw the annotated diagram for the feature
Write out the explanation under each
Fully explained processes will gain you double marks. 1 mark for naming the process and 1 for explaining the term but you NEED to do both to get both marks.
In a straight river channel the waters highest velocity is in the middle and just below the surface. If anything disrupts this e.g. large boulder or softer sediment, it will divert around the obstacle creating changes in speed and depth of the river (1).
This change in direction forms pools (deeper water and greater erosion) (1) and riffles (areas of shallow water with less energy and greater turbulence) (1). Once these form rivers flow from side to side in a winding course.
The outside of a bend has faster moving water so has more energy to erode(1). Hydraulic action(1), when air is compressed into the river bank causing materials to be dislodged(1) and Abrasion(1), pieces of broken-off rock thrown at the river bank causing erosion(1), occur here creating a river cliff. (1)
As the material is eroded at one bank a corkscrew-like motion of water known as helicoidal flow moves the eroded material from the outside of one meander and deposits it on the next. (1)
Water moves slower on the inside bend of a river, losing energy it deposits its load forming a river beach. (1)
Continuous erosion and deposition will create wider and wider meanders, which migrate downstream and outwards across floodplains in lateral erosion. (1)