River and Coastal Landforms Flashcards
How do interlocking spurs form?
In the upper course of the river there is more vertical (downward) erosion. The river cuts down into the valley. If there are areas of hard rock which are harder to erode, the river will bend around it.
How are meanders formed?
As the river makes its way to the middle course, it gains more water and therefore more energy. The lateral (sideways) erosion on the outside bend due to hydraulic action and abrasion causes undercutting of the bank to form a river cliff. Water on the inner bend is slower, causing the water to slow down and deposit eroded material, creating a gentle slope of sand and shingle, this is known as a slip-off slope.
How are oxbow lakes formed?
Erosion narrows the neck of the land within the meander and as the process continues, the meanders move closer together. When there is a very high discharge, the river cuts across the neck, taking a new, straighter and shorter route. Deposition will occur to cut off the original meander, leaving a horseshoe-shaped oxbow lake.
How are waterfalls formed?
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.
How are floodplains formed?
In the lower course the river is carrying a huge amount of sediment (alluvium). When the river floods, excess water spills over the surrounding area. During flooding, the velocity of the river is reduced, it loses energy, and deposits sediment, forming the floodplain. The floodplain is shaped by the lateral erosion of meanders as they migrate downstream and by deposition of material on the inner bends.
How are levees formed?
When a flood occurs, the river loses energy. The largest material is deposited first on the sides of the river banks and smaller material further away. After many floods, the sediment builds up to increase the height of the river banks and bed.
How are wave cut platforms formed?
The sea attacks the base of the cliff between the high and low water mark. A wave-cut notch is formed by erosional processes such as abrasion and hydraulic action - this is a dent in the cliff usually at the level of high tide. As the notch increases in size, the cliff becomes unstable and collapses, leading to the retreat of the cliff face. The backwash carries away the eroded material, leaving a wave-cut platform.The process repeats. The cliff continues to retreat.
How are headlands and bays formed?
Formed on Discordant coastlines where more resistant rock such as chalk and limestone take a long time to erode and therefore create the headlands whilst bays have softer rock such as sand and gravels therefore they erode quicker.
How are caves, arches, stacks and stumps formed?
Caves, arches, stacks and stumps are erosional features that are commonly found on a headland. Cracks are formed in the headland through the erosional processes of hydraulic action and abrasion. As the waves continue to grind away at the crack, it begins to open up to form a cave.The cave becomes larger and eventually breaks through the headland to form an arch. The base of the arch continually becomes wider through further erosion, until its roof becomes too heavy and collapses into the sea. This leaves a stack (an isolated column of rock).The stack is undercut at the base until it collapses to form a stump.
How are rock pools/potholes formed?
They are formed when sediment and other material carried by a rivers and coasts scour the floor. Where exist in the channel floor turbulent flow can cause pebbles to spin around and erode hollows through abrasion As the holes get bigger even bigger debris can become trapped in the pothole and this material further supports erosion.
How is a beach formed?
LSD (longshore drift) When constructive waves lose their energy the sand and shingle are deposited normally in sheltered areas such as bays
Describe the formation of a spit
Spits are formed where the prevailing wind blows at an angle to the coastline. Sediment is carried by longshore drift and moves along the beach via swash and backwash When there is a change in the shape of the coastline, deposition occurs.
Describe the formation of a bar
A spit can grow across a bay, joining two headlands together. This landform is known as a bar. They can trap shallow lakes behind the bar, these are known as lagoons. Lagoons do not last forever and may be filled up with sediment. Longshore drift occurs as waves push sediment (which may consist of sand, silt, and clay) towards the coastline at an angle. Instead of landing on the beach, this sediment begins to build up between the beach and an island, creating the bar mentioned above and effectively “tying” the island to the mainland.
