For Questions on the Fluvial Processes of Erosion, the landform we learn is Waterfall Formation.
For Questions on the Fluvial Processes of Deposition, the landform we learn is Delta Formation.
For Questions on Surface Processes (Flood Control) - go back and click on the Hydroelectric Power square and learn The Three Gorges Damn Case Study.
For questions on Fluvial Rejuvenation - go back and click on the Isostasy square.
Rivers HL Questions.pdfRivers HL Questions with marking-scheme.pdfFeatures of Fluvial Erosion - Waterfalls
A waterfall is a vertical drop in a river's course
(S) It forms in the youthful stage of a river.
(D) The steep gradient causes vertical erosion.
(SE) This vertical erosion helps create a distinctive waterfall feature.
A waterfall forms where hard rock lies upstream of soft rock
(S) The soft rock erodes faster than the hard rock.
(D) Examples include slate as the hard rock and sandstone as the soft rock.
(SE) This differential erosion leads to the creation of waterfalls.
Differential erosion occurs where one rock is more resistant than the other
(S) The softer rock erodes quicker than the harder rock.
(D) A notch is eroded into the soft rock.
(SE) This notch formation eventually becomes part of the waterfall’s structure.
The notch deepens over time
(S) Hydraulic action and abrasion cause this deepening.
(D) A vertical step forms as the notch grows.
(SE) This step creates the waterfall’s drop.
The vertical step increases the water's velocity as it falls
(S) The faster water gains more energy.
(D) This enhances hydraulic action.
(SE) Fast-moving water erodes the rock more efficiently.
A plunge pool forms at the base of the waterfall
(S) The force of the water breaks down the soft rock.
(D) This deepens the plunge pool.
(SE) The pool becomes a key feature of the waterfall system.
Abrasion is erosion caused by scraping or wearing away
(S) Rocks carried by the river grind against the bed and banks.
(D) The plunge pool is deepened and widened by abrasion.
(SE) This process creates a larger, deeper plunge pool.
The plunge pool is also deepened and widened during times of high discharge
(S) This can also happen due to eddying.
(D) Eddying is the swirling action of water.
(SE) Swirling water erodes the plunge pool further.
Water splashes onto the back wall of the waterfall
(S) The water dissolves minerals from the rock through solution.
(D) This weakens the back wall over time.
(SE) The waterfall becomes less stable, leading to further erosion.
Undermining of the back wall forms an overhang
(S) The hard rock becomes unsupported as the soft rock erodes.
(D) Eventually, the overhang collapses into the plunge pool.
(SE) This collapse adds debris to the waterfall system.
The collapse adds debris to the plunge pool
(S) The debris increases abrasion in the pool.
(D) This further deepens the plunge pool.
(SE) The process continuously shapes the plunge pool.
The waterfall retreats upstream as the overhang collapses
(S) Each collapse causes headward erosion.
(D) The waterfall slowly shifts upstream.
(SE) Over time, the waterfall migrates backward along the river.
If headward erosion happens quickly, a steep-sided gorge may form
(S) An example is the Grand Canyon, which is 1.6 km deep in places.
(D) The gorge was formed by rapid erosion.
(SE) Gorges are striking examples of rapid waterfall retreat.
An example of a waterfall is Torc Waterfall in Killarney and Niagara Falls in Canada
(S) These waterfalls demonstrate the global prevalence of such landforms.
Condensed SRP Summary List for Waterfalls for Timed Exam
Formation of Waterfalls
A waterfall is a vertical drop in a river's course that forms in the youthful stage of a river due to steep gradients causing vertical erosion, creating a distinctive feature.
Differential Erosion
Waterfalls form where hard rock lies upstream of soft rock; the softer rock erodes faster, as seen with slate and sandstone, leading to the creation of waterfalls through differential erosion.
Notch Formation
Differential erosion occurs where one rock is more resistant; softer rock erodes quicker, creating a notch that eventually becomes part of the waterfall’s structure.
Deepening of Notch
The notch deepens over time due to hydraulic action and abrasion, forming a vertical step that creates the waterfall’s drop.
Increased Water Velocity
The vertical step increases the water's velocity as it falls, enhancing hydraulic action and allowing fast-moving water to erode the rock more efficiently.
Plunge Pool Formation
A plunge pool forms at the base of the waterfall as the force of the water breaks down the soft rock, deepening the pool and becoming a key feature of the waterfall system.
Role of Abrasion
Abrasion occurs when rocks carried by the river grind against the bed and banks, deepening and widening the plunge pool, contributing to its size.
Impact of High Discharge
During high discharge, the plunge pool is further deepened and widened by eddying, the swirling action of water that enhances erosion.
Dissolution of Back Wall
Water splashes onto the back wall of the waterfall, dissolving minerals and weakening the rock over time, which destabilizes the waterfall and promotes further erosion.
Formation of Overhang
Undermining of the back wall occurs as the hard rock becomes unsupported due to the erosion of the soft rock; this eventually leads to the collapse of the overhang into the plunge pool.
Debris in Plunge Pool
The collapse adds debris to the plunge pool, which increases abrasion and further deepens the pool, continuously shaping its features.
Retreat of Waterfal
The waterfall retreats upstream as the overhang collapses; each collapse leads to headward erosion, causing the waterfall to migrate backward along the river.
Formation of Gorges
If headward erosion occurs quickly, a steep-sided gorge may form, like the Grand Canyon, which showcases rapid waterfall retreat through striking geological features.
Examples of Waterfalls
Torc Waterfall in Killarney and Niagara Falls in Canada demonstrate the global prevalence of waterfalls and their significant natural beauty.
Features of Fluvial Deposition - Deltas
Sample Answer - Delta Formation
1.
(S) A delta is a landform created by deposition at the mouth of a river.
(D) As the river meets a sea or lake, its speed decreases and it can no longer carry its load.
(SE) This causes sediment to be deposited and land to build up at the river mouth.
2.
(S) Deposition is the key process that forms a delta.
(D) It happens when the river loses energy as it enters still water like a sea or lake.
(SE) The river drops its load and the sediment begins to build up layer by layer.
3.
(S) Sediment is deposited in layers depending on its size and weight.
(D) Heavy materials like sand and gravel are dropped near the river mouth, while finer silt is carried further.
(SE) This creates structured layering within the delta.
4.
(S) As the delta grows, new land is formed from the deposited sediment.
(D) The river is forced to split into smaller streams to flow around the new land.
(SE) These smaller streams are called distributaries.
5.
(S) Distributaries help to spread the river’s load across the delta.
(D) They carry water and sediment in different directions.
(SE) This allows the delta to grow out into the body of water.
6.
(S) The sediment in a delta forms three distinct beds.
(D) The bottomset bed is furthest out and made of fine materials, while the foreset and topset beds contain heavier sediment.
(SE) These beds give the delta its internal structure.
7.
(S) The shape of a delta is influenced by how and where the sediment is deposited.
(D) Some deltas are fan-shaped (arcuate), while others look like bird’s feet.
(SE) The Nile Delta is arcuate and the Mississippi Delta is bird’s foot shaped.
8.
(S) Deltas continue to grow over time as deposition continues.
(D) New sediment is constantly added, pushing the edge of the delta further into the water.
(SE) This can extend the shoreline by several kilometres.
9.
(S) Tides and currents affect the shape and size of a delta.
(D) They can carry deposited sediment away or move it to new areas.
(SE) This can change how quickly the delta grows or erodes.
10.
(S) Deltas are important for farming due to their fertile soil.
(D) The sediment is rich in nutrients which helps crops grow.
(SE) Many major farming regions, like the Nile Delta, rely on this sediment.
11.
(S) The Nile Delta in Egypt is a large and important example of a delta.
(D) It was formed by sediment dropped as the Nile River enters the Mediterranean Sea.
(SE) It supports millions of people with agriculture and freshwater.
12.
(S) A small delta also exists in Ireland at Lough Tay, Co. Wicklow.
(D) The Cloghoge River loses energy as it flows into the lake and deposits sediment.
(SE) This has formed a fan-shaped build-up of material at the lake's edge.
13.
(S) The delta’s distinct layers show the gradual build-up of material over time.
(D) Coarse material is found near the top and fine material at the bottom.
(SE) These patterns can be seen clearly in cross-section diagrams of deltas.
14.
(S) As distributaries deposit sediment further out, the delta becomes more complex.
(D) The branching river channels create a network that expands over time.
(SE) This network is key to shaping the delta and helping it develop outward.
Condensed SRP Summary List for Deltas for Timed Exam
A delta forms where a river meets a sea or lake. The river slows down and loses energy. This causes it to drop its load of sediment.
Deposition is the main process involved in forming a delta. The river can't carry its load once it enters still water. Sediment builds up at the river mouth.
Heavier materials like gravel are deposited first. Lighter materials like silt travel further. This creates layered sediment in the delt
As sediment builds up, new land forms. The river is forced to split around this land. These smaller channels are called distributaries.
Distributaries spread water and sediment across the delta. They flow in different directions. This gives the delta its fan or triangular shape.
Deltas have three sediment beds. The bottomset is made of fine clay, the foreset of sand, and the topset of coarse material. These beds form in layers as the river loses energy.
Delta shape depends on water movement and sediment load. Some are fan-shaped, others have a bird’s foot pattern. The Nile is arcuate; the Mississippi is bird’s foot.
Deltas grow as more sediment is deposited. The shoreline moves outward over time. This growth can continue for many years.
Tides and currents can reshape deltas. They carry away or move sediment. This affects how stable and large the delta becomes.
Deltas are good for farming. Sediment is rich in nutrients. This helps crops grow in places like the Nile Delta.
The Nile Delta is a large example. It formed where the Nile enters the Mediterranean. It supports farming and a large population.
Lough Tay in Wicklow also has a small delta. The Cloghoge River slows down as it enters the lake. It deposits sediment in a fan shape.
The layers in the delta show how it formed. Coarse materials are near the river mouth. Fine materials are found further out.
As more distributaries form, the delta expands. These channels help spread sediment. This process makes the delta more complex over time.
Vidoes Below for Revising Junior Cycle Rivers (Stages, Erosion, Transportation, Deposition, & Landforms)
