Geography - coasts

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Revision for coasts.

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Geography - coasts
1 Types of wave
1.1 A wave?
1.1.1 Out at sea, the wind tugs at the surface of the water, causing the wave shape to move. From this moment on, the water moves forward. When a wave moves into shallow water near the coast, it is distorted until it breaks. A wave crest is the point on a wave with the maximum value or upward displacement within a cycle. A wave trough is the minimum or lowest point within the a wave cycle.
1.1.2 Water rushes up the beach - this is called the swash
1.1.3 After it has rushed up the beach, it then drains back down the beach. This is known as the backwash.
1.1.4 What makes a bigger wave? Stronger winds Distance wind has travelled (fetch) More time wave has travelled for
1.2 Constructive Waves
1.2.1 These have a strong swash and a weak backwash. This means that the beach is filled with material, because the backwash is not strong enough to remove it.
1.2.2 They are low & long.
1.3 Destructive Waves
1.3.1 They are steep, tall & close together.
1.3.2 These have a weak swash and a strong backwash. The backwash pulls pebbles & sand down the beach when the water retreats, removing it.
2 Types of erosion
2.1 The wearing away of land by the sea.
2.1.1 Destructive waves hit the original coast line, eroding the rock with its sheer force. Because this type of wave has a strong backwash, it pulls the crumbled rock, removing it from the beach and causing the cliff to retreat.
2.2 Abrasion
2.2.1 This is the force of the bits of rock carried in the water blasting into the cliff. Bits of rock & sand in waves grind down the cliff surface like sandpaper.
2.3 Solution
2.3.1 This is a chemical reaction between the sea water & the minerals in the rocks. Acids contained in sea water will dissolve some types of rock such as chalk or limestone.
2.4 Attrition
2.4.1 This is the process of rocks hitting each other & breaking into smaller rocks. Waves smash rocks & pebbles on the shore into each other & they break & become smoother.
2.5 Hydraulic action
2.5.1 This is the force of water hitting the cliff & squeezing air into cracks in the rock. Air may become trapped in joints & cracks on a cliff face. When a wave breaks, the trapped air is compressed which weakens the cliff and causes erosion.
3 Features or erosion and their formation
3.1 Lines of weakness such as faults occur in headlands. Abrasion and hydraulic action erode the fault to form a cave. The cave is widened and deepened. The sea cuts through to form an arch. The sea erodes the foot of the arch and widens it. The roof of the arch becomes too heavy and collapses. Part of the former cliff is now isolated as a stack. Over time the stack is undercut and collapses. A stump is the remains of the eroded stack.
3.1.1 Constructive waves are involved by eroding the cliff.
3.1.2 Destructive waves are involved in this process, because of their strong backwash of pulling material away.
4 Transportation
4.1 The movement of sediment load by the sea.
4.2 Traction
4.2.1 Larger pebbles and cobbles are rolled along the sea bed.
4.3 Saltation
4.3.1 Small pebbles are moved when one pebble hits another, causing it to bounce. This bouncing can set up a chain reaction.
4.4 Solution
4.4.1 Dissolved material is carried along in solution, so you can't see it.
4.5 Suspension
4.5.1 Fine sediment is carried as a suspension in the water, making it look muddy or murky.
5 Longshore drift & spit formation
5.1 Diagram
5.2 A spit is an accumulation of sand with one end attached to the land & the other reaching out across an estuary or into the sea. They are features of coastal deposition.
5.3 Spits are formed when large amounts of sediment are transported by longshore drift & where the coastline suddenly changes direction to leave a sheltered, shallow area of water. Due to an increase in friction, more deposition can occur in the water sheltered by the headland.
5.4 Sediment is moved diagonally by the swash & backwards by the backwash. If there is a river estuary, longshore drift continues to transport the sediment. However, the river current is too strong for longshore drift to reach the other side of the estuary. Secondary winds create a hook shaped curve on the end of the spit.
5.5 Behind the spit is very sheltered. Here a salt marsh forms.
6 Mass movement & cliff collapse
6.1 When rocks loosened by weathering move down slope under the influence of gravity. The rocks can slide or slump.
6.2 Physical causes of it: rain, type of soil, waves, weathering.
6.3 Human causes of it: building, watering, planting, tourism.
7 Coastal Defence
7.1 Hard Engineering
7.1.1 Sea wall Effective, walkway. Unnatural, expensive.
7.1.2 Groynes Tourist & fishers attraction. Unnatural & interrupts longshore drift.
7.1.3 Rock armour Cheap, provides interest. Obtrusive, hard to transport.
7.1.4 Gabions
7.2 Soft Engineering
7.2.1 Sand dune regeneration Natural, cheap, popular for wildlife. Easily damaged, time consuming.
7.2.2 Managed retreat
7.2.3 Marsh creation Cheap, habitat for wildlife. Lost land.
7.2.4 Beach nourishment Cheap & blends in. Constant maintenance needed.
7.3 Destructive waves erode the bottom of the cliff, causing it to retreat. Coastal defence slows the process of erosion down.
8 Case Studies
8.1 Holbeck Hall
8.2 Hurst Castle Spit
8.3 Old Harry Rocks
8.4 Holderness Coast
9 Weathering
9.1 Chemical
9.1.1 When rain water reacts with minerals in rock and forms soft clay.
9.2 Mechanical /Physical
9.2.1 Temperature change (rock falls away like skin), freeze-thaw (pieces break off), wind, rain & waves (wear).
9.3 Biological
9.3.1 Where plants roots grow & make cracks in rook larger. Or when creatures walk /dig etc.
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