Presentation on theme: "1 COASTS. 2 What processes make coasts change shape? Erosion attrition abrasion corrosion hydraulic action Deposition traction saltation suspension solution."— Presentation transcript:
2 What processes make coasts change shape? Erosion attrition abrasion corrosion hydraulic action Deposition traction saltation suspension solution Transportation
3 Erosion How easily a coast is eroded depends on how hard the rock is Capes and Bay! There is an animation of this on the blog!
4 Studland Bay – and you can see in the distance some rocks we will be looking at later – those are chalk cliffs with a soft sandstone
5 Erosion: which is which? The sea picks up stones and throws them against the cliff wearing it away. The waves force air into cracks in the rock and the pressure causes the rocks to split and break up. Boulders already eroded from the cliffs are broken down into smaller and more rounded particles. Rocks are dissolved by the chemical content of the water.
6 How cliffs are eroded Wave-cut notch The tougher rocks of the headlands are gradually eroded away by attrition, hydraulic action (and sometimes corrosion, e.g. limestone or chalk) and gradually a small Wave-cut notch is made by the waves at high tide As it gets bigger, the overhanging rock will eventually tumble into the sea.
7 How cliffs are eroded wave-cut platform Over time the cliff retreats leaving a wave-cut platform just below the surface, that shows only when the tide is out This is in Dorset near Purbeck at Kimmeridge Bay.
8 There are some special coastal features These form where chalk or limestone form the hard band of rock. Here the erosion is help by corrosion. If the water is slightly acid, then the calcium carbonate that makes up these rocks will dissolve slowly. The rocks were laid down millions of years ago in a warm sea and are made mostly of the shells of molluscs.
9 cliff crack cave
10 arch pillar stack
11 stump reef
12 original photo Holei Sea Arch Can you remember the order? C P S R
13 Some examples What do all these show from Selwick?
14 What happens next? Once the rock has been eroded away from the cliff by abrasion and corrosion and hydraulic action The pieces will be further broken down by attrition, becoming smoother and smaller over time Some of it will be transported away and deposited somewhere else Broken rock ends up on beaches as sand or shingle (round pebbles)
15 But beaches do not stay the same Most of the waves break on the beaches at an angle. constructive, Some of the waves are constructive, which means they bring material from another place and leave it. swash waves These waves have powerful swash waves – waves that drop anything they are carrying as they break These make beaches bigger.
17 But beaches do not stay the same destructive, Some of the waves are destructive, which means that they break on the beach and as the water runs back, it drags part of the beach away with it. backwash waves These waves have powerful backwash waves – big waves that make more noise as they retreat, taking the sand and shingle with them. These make beaches smaller.
19 But beaches do not stay the same Some waves are a bit of both. This is called longshore drift
20 Longshore Drift Visit For 100s of free powerpoints
22 Direction of swash
23 Direction of swash
24 Direction of swash Backwash Direction of swash Backwash
25 Direction of swash Backwash Longshore Drift Direction of swash Longshore Drift
26 Direction of swash Longshore Drift Groyne traps sediment Build up of sediment against the groyne
27 And this happens if the long shore drift is allowed to carry on The coast changes direction But the long shore drift carries on But the load gets dropped as the longshore drift looses power Deposits and seed are caught behind the shingle bar and a salt marsh begins to grow This is called a spit
28 What can happen with longshore drift? As the River Humber joins the North sea
29 What can happen with longshore drift? The sand and shingle are dragged down the coast from the NW. The blue line shows a shingle bank tombolo. It continued across the gap between the main land and the island to form a tombolo.
30 Homework for 2 weeks up to the end of half term If possible (if not we need to talk). To visit the coast and to gather photographic evidence or you can sketch it and scan it if you like. Now I want the evidence annotated, which means not just labels but explanations too. See over for an example
31 Walton on the Naze Soft rock that is being eroded Fine sand has been deposited This trees roots soil was eroded away so it fell over
33 So what could you take pictures of to show beach features? Evidence of erosion (or not like cliffs ) Evidence of deposition Beaches – pebbles – cliffs – sand dunes – groynes – longshore drift - spits Remember AND Annotate = label AND explain