Creation of different landforms Flashcards
What sort of cliffs do horizontally, seaward dipping and landward dipping strata produce
Horizontally bedded strata - undercutting of cliffs creating steep cliffs
Seaward dipping strata - slumping occurs rocks loosened by weathering slope into sea
Landward dipping strata - takes a long time to erode the slope profile is gradually lowered by weathering and mass movement
How is a headland formed
On a discordant coastline there is differential erosion between 2 different rock types for example peveril point is on portland limestone whilst swanage bay is on chalk
How is a cove formed
On a concordant coastline the hard rock acts as a shell to the soft rock. When the waves break through the rock then the soft clay behind is easier to erode. Lulworth cove portland limestone protects wealden clay behind. The portland has been broken and the soft wealden clay has been eroded to create Lulworth cove that has an 125 metre entrance is 500 metre wide and has cliffs 75-100 metres high
How are Geos created and blowholes created
lines of weakness in rock like joints or faults . Weak points are eroded more rapidly by wave action and hydraulic action A cave is then formed. Then continuous weathering and erosion causes the cave to be expanded into the cliff and the ceiling of the cliff to be eroded. One example of this is Huntsman’s leap Pembrokeshire. A blowhole is created when a part of the roof of the cave falls in this creates a tunnel for water to flow up through
How are arches stacks and stumps formed
Due to wave refraction energy is concentrated on the headland. Any weaknesses on the rock like joints or faults a small cave may develop. If the cave ends u breaching the other side of the headland an arch is formed. Continued erosion of the base of the arch and weathering along the top of the arch causes mass movement (rockfall) This creates a stack. Continued erosion/ weathering of the stack then causes more rockfall to create a stump.
Give examples of a stack a stump and an arch
Old Harrys rocks - 2.5 km NE Swanage
- old Harrys wide is now a stump after falling in 1896
- old harry is a stack
Made of limestone
Durdle door - arch
150 million years old
60 metres tall
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What are the 3 main sources of sediment for beaches
5 percent cliff erosion
5 percent offshore sources
90 percent rivers
sand produces beaches with a gentle slop <5 percent as its small size allows for little percolation sand so less friction so water and sand is dragged back down the beach and deposited evenly
How is a spit formed
Spits are long narrow beaches that extend over an estuary indentation in coastline or when the coastline changes direction. They are formed when longshore drift happens and sediment is deposited along the coastline. Typically a spit will have the biggest sediment where the prevailing wind. Longshore drift is when the waves come in with the prevailing wind and then travel at a 90 degree angle back out to sea. This process continues down the beach until the indentation is met. The spit then keeps going becoming an extension of the mainland. Secondary wind directions can cause the spit to have a recurved hook.
One example of a spit
Spurn head projects for 4 miles and is as little as 50 metres wide formed over Humber estuary
How is a salt marsh formed
When water mixes with fresh water behind a spit when a spit crosses an estuary. Behind spurn point there is a salt marsh. Form on low-energy environments UK has 45,500 hectares of salt marsh. Eelgrass present mix of sand and clays subject to rise and fall of tides
How do onshore-bars form
If a spit continues to grow over an indentation so that a lagoon is created on the landward side. One example of this is the 100 metre wide bar at slapton sands that is 5km long
How are tombolos formed
When a spit grows and reaches an offshore island one example is the tombolo at Marblehead in Massachusetts USA and chesil beach near Weymouth Dorset however this is unlikely to have been formed by LSD as the south westerly prevailing wind means that there should be larger rock on the west part of the beach. However this is not the case. Onshore migration of sediment is therefore more likely
