IGCSE Geography 0460

2. The Natural Environment

2.2 Rivers: Explain processes and landforms associated with river erosion and deposition.

Rivers are powerful agents of erosion and deposition, shaping the Earth's surface over time. This section explores the processes involved in these transformations and the distinctive landforms they create.

River Erosion

River erosion is the process by which a river wears away and transports material. The main processes involved are:

• Hydraulic Action: The force of the water itself impacting on the riverbed and banks. This can dislodge rocks and sediment.
• Abrasion: The wearing away of the riverbed and banks by sediment carried in the water (sand, pebbles, etc.).
• Attrition: The wearing down of the sediment carried by the river as the particles collide with each other.
• Solution (Corrosion): The dissolving of soluble rocks like limestone by acidic rainwater and river water.

The rate of erosion depends on factors such as the volume and velocity of the water, the type of rock, and the presence of sediment.

Landforms Associated with River Erosion

River erosion creates a variety of distinctive landforms:

• V-shaped Valleys: Formed in mountainous areas where the river has a high velocity and is actively eroding downwards. The valley sides are steep.
• C-shaped Valleys: Formed in glacial valleys that have been widened and deepened by rivers flowing through them.
• Waterfalls: Occur where a river flows over a layer of resistant rock overlying a softer rock. The softer rock is eroded more quickly, creating a steep drop.
• Gorges: Deep, narrow valleys with steep sides, often formed where a river erodes through resistant rock.
• Entrenchments: Occur where a river flows through a valley that has been eroded by a tributary valley. The river becomes entrenched, meaning it cuts down into the valley floor.

River Deposition

River deposition is the process by which a river drops the sediment it is carrying. This happens when the velocity of the water decreases.

Deposition occurs in areas where the river loses energy, such as in wider sections of the river channel or where the gradient decreases.

Landforms Associated with River Deposition

River deposition creates a range of landforms:

• Alluvial Fans: Fan-shaped deposits of sediment that occur where a river emerges from a confined channel onto a flatter area.
• Floodplains: Flat areas of land adjacent to a river channel that are formed by the deposition of sediment during floods.
• Levees: Natural embankments of sediment that form on the sides of a river channel during floods.
• Deltas: Formed at the mouth of a river where it enters a lake or the sea. The river's velocity decreases, causing sediment to be deposited. Deltas can be triangular (river deltas) or fan-shaped (coastal deltas).

Landform	Process	Description
V-shaped Valley	Erosion	Found in mountainous regions, with steep sides and a narrow bottom.
Waterfall	Erosion	Forms where a river flows over alternating layers of hard and soft rock.
Floodplain	Deposition	Flat land alongside a river, formed by sediment deposited during floods.
Delta	Deposition	Fan-shaped or triangular landform at the mouth of a river, formed by sediment deposition.

Understanding the processes of river erosion and deposition is crucial for analyzing landscapes and assessing flood risk.