Formation of features Flashcards
How is a waterfall formed?
They occur where a band of hard rock overlies a softer rock. Erosion processes such as Hydraulic Action and Abrasion erode the softer rock is quicker than the harder rock and gradually washes away downstream.
This creates a plunge pool where any rocks and debris swept into the plunge pool by the river will be swirled around and rub against the bed and banks of the plunge pool, deepening it further. Over time, the softer rock is eroded further creating an over hang of hard rock. This overhang is unstable as it’s weight is unsupported. Eventually, this hard rock collapses because it is unsupported and the waterfall moves back upstream.
How is a gorge formed?
The waterfall formation continues and it begins to retreat upstream leaving behind a steep sided gorge.
How is a meander formed?
Lateral erosion causes kinks in the river. The water on the outside bend moving more quickly meaning it has more energy to erode the river bank on the inside the water travels more slowly causes depostion. after time the bend get tighter and tighter.
How is an oxbow-lake formed?
When the water level is high (or during a flood) the meander is cut off and the river takes the easiest route. The ox-bow lake often drys up.
How are levees formed?
when a river flood it deposits the material its transporting, due it having less energy. The heaviest material is deposited closest to the river and over many flood this material builds up into levees.
How are deltas formed?
only under certain conditions at the mouth of a river. deltas are built up over time as sediment s are deposited at the mouth of the river causing the river to be split into 100’s of different channels.
How is a “v” shaped valley formed?
vertical erosion causes a narrow gorge the sides are weathered making it less steep and more of a “v” shape.
How is a wave cut platform formed?
Cliff face is eroded by solution, hydraulic action and abrasion weakening the cliff. This cliff breaks away leaving a wave cut notch, erosion continues and the cliff is undercut until it eventually falls leaving a wave cut platform.
How are Stacks. stumps, arches, and caves formed?
A line of weakness is eroded and it widens and deepens into a cave. Erosion continues through the processes of corasion and hydraulic action until it extends all the way through to form and arch. The roof of the arch is weathered and the weight eventually becomes too much causing it to collapse forming a stack. Erosion continues until a stump is left.
How is a cove formed?
When rocks run in horizontal bands. The sea erodes the layer of harder rock using solution and hydraulic action. When it reaches the softer rock it is eroded quicker and this leaves a circular cove with a narrow entrance
When is deposition likely to occur?
When: waves enter shallow water, waves enter a sheltered area, there is little wind, there’s a good supply of material
How is a spit formed?
Longshore drift carries sediments along the coast. The swash moves material up the coast in the direction of the prevailing wind. If the coast changes direction, sediment continues to be dropped in the same direction. Meaning a long thin ridge of material is deposited- this is the spit. A change in wind direction can cause a hooked end.
How is a Bar formed?
A bays is formed so longshore drift moves material between the two headlands in the direction of the prevailing wind. This forms a spit and eventually the spit will reach the second headland. A lagoon can form behind the bar.
How is a tombolo formed?
When a spit continues to grow outwards joining to an offshore island. This requires the island to be located at the mouth of a river.
How is a beach formed?
Beaches are made up of eroded material that has been transported from elsewhere and deposited by the sea.
Constructive waves help to build up beaches.
