CORE UNIT: PATTERNS AND PROCESSES IN THE PHYSICAL ENVIRONMENT
erodes the outer bend with more force. Hydraulic action and abrasion can cause undercutting, creating a steep river cliff which is cut into the bank. Hydraulic action also forces bubbles of air into the river bank, creating shock waves inside the bank. This is called cavitation. This further loosens the bank and some falls away. The continued undercutting of the bank leads to its collapse (bank caving) and a widening of the river channel (lateral erosion). The speed of flow is much slower on the inside bend causing deposition. Asmall
beach called a point bar is deposited on the inside bend. This point bar further deflects the fast-moving water to the outer bend, increasing lateral erosion there. Gradually, the riverwanders over its flood plain in a series of sweepingmeanders.
The continuous erosion and deposition makes the meanders move across the landscape a bit like a snake. These are called migrating meanders.
Flow is fast. Causes undercutting of river bank and formation of river cliff
CROSS SECTION Point bar
River cliff Undercutting
Point bar
Flow is slow at inner bank. Leads to deposition and formation of point bar
Fig. 29 Exam Diagram: The development of meanders
Slow upward current deposits material
River cliff
Strong, fast, downward current scrapes at the river bank
ACTIVITY
Look at the photograph. Identify a point bar and a river cliff.
Fig. 30 Map to show meanders on a river near Poundcarton, County Donegal