River Landforms (SL IB Geography)

Waterfalls

• Occur on horizontally bedded rocks
• Soft rock is undercut by hydraulic action and abrasion
• Due to the weight of the water and no support, the waterfall collapses and retreats upstream
• Over thousands of years, waterfalls may create a gorge

Formation of a waterfall

 

The formation of a waterfall

Meanders

• Meanders are formed in rivers due to the combination of erosion and sediment deposition processes
• The river erodes the outer bank of a bend, creating a cutbank
• Deposition occurs along the inner bank, forming a point bar
• As the water flows faster along the outer bend (cutbank) it erodes the bank more, deepening the channel
• Sediment is deposited along the inner bend (point bar), causing the bank to build up
• Over time, erosional and depositional processes cause the river to develop a sinuous, meandering course

Cross-section through a meander

Meander formation

Floodplains

• When a river floods, a floodplain is formed
• Alluvium is a mixture of sand and gravel that is eroded on the outside of the meander
• Floodplains are built up by channel deposition
• Floodplains consist of finer materials

Levees

• A landform of deposition
• Levees are raised banks
• Coarse material is deposited near the channel
• Finer material is deposited and carried to the floodplain
• Levees are found on the edge of the river
• They are formed by repeated flooding
• When a river floods, the river’s energy is reduced
• Coarse material is dropped first and then lighter material 
• Over time, the levees build up from coarse material

Floodplain and levee formation

The formation of floodplains and levees

Deltas

• Deltas are formed when streams flow into standing bodies of water
• Rivers must carry a large amount of sediment for deltas to form
• Flocculation increases deposition
• Bioconstruction increases deposition
• Delta formation must have a rapid drop in stream velocity
• There are a variety of delta formations, such as arcuate and bird’s foot

Types of delta