Formation of river landforms Flashcards
Waterfalls
The soft rock is eroded quicker than the hard rock and this creates a step.
As erosion continues, the hard rock is undercut forming an overhang.
Abrasion and hydraulic action erode to create a plunge pool
Over time this gets bigger, increasing the size of the overhang until the hard rock is no longer supported and it collapses.
This process continues and the waterfall retreats upstream.
A steep-sided valley is left where the waterfall once was. This is called a
gorge.
GEOMORPHIC PROCESS:
- Hydraulic action
KEY PHRASES:
- Increased energy in the river leads to the waterfall retreating over time and the formation of a gorge
-Increased energy leads to increased hydraulic action, which creates for an even steeper gradient between hard and soft rock
EXAMPLE: High force
DIAGRAM:
Gorges
Formed when waterfalls retreat upstream over time. This happens when the softer rock is eroded and the resulting overhang of hard rock becomes too heavy and falls into the water below.
GEOMORPHIC PROCESS/ES
-Hydraulic Action
KEY PHRASES:
- Increased energy in the river leads to lateral erosion in the form of hydraulic action. Which leads to the waterfall retreating over time and the formation of a gorge
Example: Gorge at high force
DIAGRAM:
V-Shaped Valley
1-Vertical erosion occurs in the upper course, due to the low discharge, which means that the river only has enough energy to erode downwards in the form of hydraulic action, solution
2- The valleys are slowly broken down through weathering- For example Freeze Thaw Weathering
3- The weathered material is transferred down towards the river via gravity in the form of slipping and mass movement
4- The steep-sided and narrow valley that is created is typical of upland rivers
GEOMORPHIC PROCESS/ES
- Vertical erosion- Hydraulic action (Solution)
-Freeze Thaw weathering
-Slipping
- Mass Movement
Example:
Cauldron Snout
DIAGRAM:
Floodplain
A floodplain is a wide, flat area of land either side of a river in its lower course. The floodplain is formed by both the processes of erosion and deposition. Lateral erosion is caused by meanders and their associated river cliffs and the slow migration of meanders downstream. Deposition occurs on the slip-off slope (the sediment deposited on the inside of a meander) and when the river floods and the increase in friction on the flood plain causes the flood waters to deposit the sediments they are carrying.
GEOMORPHIC PROCESS/ES
- Lateral erosion
- Deposition
DIAGRAM
Levee
When there is a heavy rainfall event in a drainage basin, a river’s cross-sectional volume will increase from its normal flow to bankfull stage and then spill over the banks to be in flood conditions. These flat floodplains, which are a result of the lateral erosion caused by meander migration, will get alluvial deposits on them from the floodwater. The water that spills on to the flat land decreases its velocity due to increased friction with the surrounding land. When this decreases, so does the river water’s carrying capacity leading to deposition. The heaviest material will be deposited first, nearest the river channel as it requires the highest velocity for entrainment. As you move further from the river channel, the material will become smaller and smaller and the levee (this sinuous ridge of deposited material) will thin the further you get from the channel.
GEOMORPHIC PROCESSES:
Lateral erosion,
Deposition
DIAGRAM
Meander
As a river goes around a bend, most of the water is pushed towards the outside. This causes increased speed and therefore increased erosion (through hydraulic action and abrasion).
A steep bank called a river cliff is created on the outside of the meander.
The lateral erosion on the outside bend causes undercutting of the
river cliff leaving an overhanging bank.
Water on the inner bend is slower, causing the water to deposit eroded material, creating a gentle slope of sand and shingle.
The build-up of deposited sediment is known as a
slip-off slope
(or sometimes river beach).
Ox-Bow Lake
Over time meanders grow larger due to erosion (Hydraulic Action+Abrasion) on the outside of river bends and deposition on the inside of the bends. This can cause the bends to make closer to each other.
Eventually, the river may take a shortcut, cutting across the narrow neck of the meander loop. This often happens during a flood
Deposition leaves a separated oxbow lake, when the oxbow lake dries up, a meander scar is left
GEOMORPHIC PROCCESES:
Deposition
Hydraulic Action
Abrasion
DIAGRAM:
Headland and bays
A headland is formed on a discordant coastline when there are layers of hard rock adjacent to layers of soft rock.
Hard rock is less resistant to erosion, in comparison to soft rock, so more energy is concentration because the waves curve towards them as they enter shallow water.
This means that the sediment is deposited in the bays creating beaches.
After many years of erosion (Hydraulic action+ Abrasion) the layers of soft rock on the coastline will have eroded much more, and there will be headlands made op of hard rock.
Geomorphic Process/es:
Hydraulic Action+ Abrasion
Deposition
Example: Durlston head and Swanage Bay
DIAGRAM
Spits
Spits are created when the coastline ends and the process of longshore drift continues, so sediment is deposited off the coast.
If the conditions are right, this sediment will build up to form new land which will extend out along the existing coastline.
The end of the feature will be curved by wave action and the impact of winds.
CONDITIONS:
Large volumes of sediment of different sizes available
Rapid rate of movement of sediment along the coast
low wave energy
Example: Chesil Beach
GEOMORPHIC PROCESSES:
Deposition
DIAGRAM
Cave–> Stump
Cracks are formed from the widening of Weak points in the headland as a result of Hydraulic action, Abrasion and Chemical weathering.
The cracks will be enlarged as a result of wave refraction, enlarging it into an cave.
Eventually the cave will extend into the headland to create an arch.
The larger the arch becomes, the more unstable it is. Eventually, due to heavy rainfall and weathering the roof of the arch will collapse.
When this occurs, a standing section of rock known as stack. The base of the stack is very vulnerable to hydraulic action and abrasion. This causes it to get narrower.
In extreme conditions, the stack can break off, forming a stump
GEOMORPHIC PROCESS/ES:
Abrasion
Hydraulic Action
DIAGRAM
Beach
A beach can form on a low low lying coast if loose material such as gravel or sand is available. This could be carried onto the shoreline by the swash effect of waves. As the waves slow down their energy drops and this material is deposited. The backwash effect of the waves can extend the beach by longshore drift.
KEY PROCESSES:
Deposition
Swash
Backwash
DIAGRAM
