River Environments - 1.2 (Fluvial Processes, River Landscapes)

Fluvial Processes

Weathering Processes

Physical Weathering	Breaks rocks down into smaller pieces by changes in temperature and by thawing water
Chemical Weathering	Happens when chemicals react with water, dissolving the rock and weakening it
Biological Weathering	The roots of plants, especially trees, and burrowing animals split the rocks apart.

Mass movement

Rock Falls: Fragments of rock are continually weathered and eroded until they separate and fall from the cliff as whole parts.

Slumping: The bottom of a valley side slope is cut away by the river flowing at its base making the slope unstable and weathered material slumps down towards the river. Slumping is also helped when the weathered material on the slope is saturated by heavy rain.

Soil Creep: Gravity pulls down the weathered material on the slope downwards to the river, where it is eroded. 

Erosion

Hydraulic Action	The force of water in the channel hitting the bed and banks gradually wears them down
Abrasion	The scraping away of the river bed and banks by stones carried in the river flow
Corrosion (Solution)	The dissolving of minerals in the rocks in the bed and banks which are carried away in solution

Transportation

Traction: Heaviest material is rolled along the riverbed. This requires the most energy

Saltation: Sand particles are bounced along

Solution: Minerals dissolved in the water are carried along

Suspension: Small particles are carried within the current

✩ Deposition - The process where material is dropped after being transported by the river current. The material is called sediment

River Landscapes

Upland Landforms

Waterfalls: Occur where a band of hard rock is much more resistant to erosion than the softer rock below it. This softer rock is readily eroded by the force of the water as it falls over the hard cap rock. Gradually, the falling water excavates a plunge pool at the bottom of the falls. Slowly, the hard rock is eroded back by the river and so the waterfall gradually retreats upstream leaving a gorge behind it. 

Interlocking spurs: Formed when the river swings from side to side. The main work of the river is cutting vertically downwards into its bed. This means that the river cuts down to flow between spurs of higher land on alternate sides of the valley.

Lowland Landforms

Levees: When a river floods, friction increases on the bank and so increases the deposition across the valley floor. The largest amount of deposition is always in the banks of the river channel. The deposition accumulates, building up the sides of the channel, forming levees. Deposition farther than the levee makes floodplains.

Oxbow Lakes and Meanders: The force of water undercuts the bank on the outside of the ricer, eroding it laterally and pushing the bend farther and farther out. On the inside of the bend, the water moves more slowly, creating more friction and so deposits material. As this erosion and deposition continue, the old meander bend is left isolated from the main channel as an ox-bow lake, and deposition gradually seals off the old meander bend forming a straighter river channel.