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.
Describe the formation of an arête:
An arête is a ridge of land between two glacier valleys or at the back of a corrie.
It forms due to the erosional processes (abrasion and freeze thaw weathering) occur on two adjacent corries/ glacier valleys. Basal sliding occurs on both corries, meaning that abrasion occurs on the steep back wall, making them more vertical and the corries deeper, which forms the thing ridge.
Describe the formation of a pyramidal peak:
When three corries or glacier valley’s meet at one point and their arêtes all join up in a single mountain peak. Due to the basal sliding and rotational slip, plucking and abrasion occur making the glaciers deeper and freeze thaw weathering occurs no the back walls making them more vertical and the pyramidal peek pointed and distinguished.
Describe the formation of a glacial trough:
-As a glacier progresses down a V-shaped valley due to gravity, the processes that occur can shape the landscape differently.
-As a glacier collects more snow, it compresses and becomes denser, this increases its erosional power to abrade and pluck away at the valley grinding the floor, making it deeper.
-Over time the glacier will abrade and pluck at the sides of the V-shaped valley, making the walls more vertical and rocky.
-The valley floor also gets abrades downwards by the sediment at the bottom of the glacier making the floor wider and flatter.
-Plucking occurs, breaking pieces of the valley off from the sides and bottom by the meltwater freezing around rocks, which gives the glacier more erosional tools as it gets transported down the glacier.
-When the glacier retreats and melts away it reveals a U-shaped valley, a glacial trough, characterised by its deep vertical sides and its flat valley floor. In the middle is a misfit river, which no longer fits in with the huge disproportionate valley. Above, glacial tributaries have also melted away, leaving hanging valleys which waterfalls fall from into the misfit river below.
-The moraine that the glacier has deposited is fertile, which vegetation can grow from.
Describe the formation of a drumlin:
A drumlin is an egg-shaped mound of glacial till that has collected in groups forming a hill like shape on the glacier floor. They are characterised with a toss end (a steep end) and a tapered end, this is caused when the glacier snout approaches a stickier, well saturated part of the ground, making the till more mouldable. It bulldozes this sediment collecting it in a mound until the glacier starts to progress and climb over the mound, due to the glacier’s weight the mound gets flattened on one side creating the tapered side of the drumlin which is revealed once the glacier melts away.
Describe the formation of a ribbon lake:
Ribbon lakes are long thin lakes where water has collected into depressions caused by the abrasion and plucking of the previous glacier.
This is when the geology of the glacier bed is made of a pocket of softer rock surrounded in harder rock, this makes it more susceptible to abrasion and plucking from the glacier ad its sediments trapped underneath. This creates a depression in the glacier bed which gets deeper and deeper, as the glacier leaves the depression, due to more friction, the glacier stats to deposit till on the other side of the depression forming a lip which will act as a dam when the glacier melts away, exposing the ribbon lake.
