3.3.2. River landforms

What shape do river valleys typically have in the upper course?

V shaped

What are upper course river valley sides are often loosened by?

Freeze thaw weathering

What dramatic landforms occur where a river flows across bands of contrasting hard and soft rock?

Waterfalls  and  gorges 

Order the stages of waterfall formation:

1. Differential erosion of soft rock

2. Undercutting and plunge pool formation

3. Collapse of the hard rock overhang

4. Retreat upstream to form a gorge

What deep feature is carved out at the base of a waterfall by swirling boulders?

Plunge pool

What narrow, steep-sided valley is formed as a waterfall retreats upstream over thousands of years?

Gorge

What is the term for the fastest-flowing current in a meander?

Thalweg

Which processes occur on the outside bend of a meander?

• Hydraulic action

• Abrasion

Order the stages of ox-bow lake formation:

1. Continuous lateral erosion narrows the meander neck

2. During high discharge, the river cuts through the neck

3. The river establishes a new straighter channel

4. Deposition seals off the abandoned loop

5. An isolated ox-bow lake is formed

What triggers the breakthrough of a meander neck to form an ox-bow lake?

A flood or high discharge

What is a meander scar

An ox-bow lake that dries up over time

What depositional landforms found in the lower course?

• Floodplains

• Levees

• Estuaries

What fine, mineral-rich silt is deposited during floods in the lower course?

Alluvium

What naturally raised embankments run parallel to the river channel on a floodplain?

Levees

What is the transitional zone where fresh river water meets the open sea?

Estuary

What mixture of fresh and salty water is found in an estuary?

Brackish water

What fine, nutrient-rich sediment features are exposed at low tide in an estuary?

Mudflats