How are river landforms formed?

Rivers shape the landscape through erosion, transportation and deposition. These processes interact differently along the river’s course, forming a range of fluvial landforms.

River Erosion Processes

• Hydraulic Action: The force of water hitting the riverbanks compresses air into cracks, breaking the rock apart.
• Abrasion: Stones and sediment carried by the river scrape the bed and banks like sandpaper.
• Attrition: Rocks carried by the river knock against each other, becoming smaller and rounder.
• Solution (corrosion): Minerals in rocks (especially limestone) dissolve in the river water.

Transportation Processes

Rivers carry sediment (also known as load) by different methods, depending on the river’s energy:

• Traction: Large boulders are rolled along the riverbed.
• Saltation: Pebbles and small stones are bounced along the bed.
• Suspension: Fine, light sediment is carried within the water.
• Solution: Dissolved materials are carried invisibly in the water.

Deposition

Deposition occurs when a river loses energy, causing it to drop its load. This happens in:

• Low-flow conditions (e.g. droughts)
• Inside bends of meanders
• The lower course near the mouth

Landforms Created by Fluvial Processes

Meanders and Oxbow Lakes (Middle Course)

Meanders are wide bends in a river, formed by lateral erosion on the outside bend (due to faster flow and erosion) and deposition on the inside bend (where flow is slower).

• Over time, erosion narrows the neck of the meander.
• During high flow, the river may break through and create a new, straighter channel.
• The old meander loop is cut off and becomes an oxbow lake.
• Processes involved: Hydraulic action, abrasion, deposition

Waterfalls and Gorges (Upper Course)

Waterfalls form when hard rock overlays soft rock. The soft rock erodes faster, creating a step in the riverbed.

• Undercutting forms a plunge pool below the waterfall.
• Eventually, the overhanging hard rock collapses.
• This repeats, causing the waterfall to retreat upstream and leave a steep-sided gorge.
• Processes involved: Hydraulic action, abrasion

Interlocking Spurs (Upper Course)

• In hilly areas, the river winds around areas of harder rock, creating a zig-zagging path.
• These hills that jut out are called interlocking spurs.
• Processes involved: Vertical erosion, limited lateral erosion

Floodplains and Levees (Lower Course)

• A floodplain is the wide, flat valley floor on either side of a river.
• During floods, sediment is deposited across the plain, building up fertile alluvial soil.
• After repeated flooding, natural embankments called levees can form next to the river channel as heavier sediment is deposited first.
• Processes involved: Deposition (mainly), suspension, solution

Deltas (River Mouth)

• A delta forms where a river meets the sea or lake, and its velocity suddenly drops.
• Deposition builds up sediment faster than it can be removed.
• Over time, this forms distributaries and creates a fan-shaped delta (e.g. the Nile Delta).
• Processes involved: Deposition, suspension, solution