Landforms Flashcards
Describe how a waterfall is formed:
Waterfalls are located where the geology contains bands of more and less resistant rock that a river passes over in the upper course.
-As the less resistant rock is more prone to erosion, the river vertically erodes (due to gravitational potential energy) through abrasion and hydraulic action. As the more resistant harder rock is less prone to erosion it isn’t eroded.
-This means that the river creates a step, where the softer rock erodes down leaving a ledge of harder rock behind.
-As the water falls to the bottom of the step, hydraulic action and abrasion occur creating a plunge pool, which grows as the water falls in it as sediment grinds along th edges.
-Over time the plunge pool recedes, and the water undercuts the overhang of harder rock, making the ledge unstable and eventually it breaks off.
-Since the harder rock ledge collapses into the plunge pool this means that it has more erosional power and tools to erode further, making it bigger.
-All this results in the waterfall retreating backward into the source, leaving behind a gorge as it migrates back and rapids at the bottom.
Describe how a meander forms:
Meanders are found in the middle to lower course where the river starts to wind around the land.
-On the outer bend, the thalweg (where the water flows the fastest) is located. It has lots of energy due to centrifugal force and therefore erodes due to abrasion and hydraulic action.
-On the inner bend the river has less energy as it is shallow therefore has more friction so it deposits its sediment onto the river bed, creating a slip off slope.
Describe how levées are formed:
In the lower course, if a river floods, the water bursts the rivers banks a floods over the flood plains. As the water moves away from the river channel, it experiences more friction and loses its energy, bigger species of sediment are deposited besides the river as the river doesn’t have enough energy to transport it further unlike smaller, lighter sediment which can be carried further away. This creates a ridge of sediment either side of the river channel which is called a levée.
Describe how flood plains are formed:
They are formed when the river in the lower course floods and deposits its sediment (alluvium) onto the valley floor, making it higher. A flood plain is a wide valley floor that a meander can widen even more as it meanders.
Describe the formation of an estuary:
-In the lower course, the river’s velocity is very high so it can transport large sediments in its flow.
-As the river approaches the sea, and especially at hight the, the river’s velocity decreases rapidly and it deposits all of its sediments to the ground.
-Over time the sediment layers, and at low tide can be exposed as mudflats which habitats can grow from, creating salt marshes. These however can be eroded away easily by strong currents.
