LESSON OBJECTIVE• Todescribe and explain the 4 coastal erosion processes 6
Erosion Corrasion3 COASTAL PROCESSES Abrasion Solution Hydraulic action Transport Longshore drift Deposition Factors: -Supply of sediment -Gradient of slope -Coast position 7
COASTAL EROSION More erosion Less erosionTypes of waves -Destructive waves -Constructive (more energy) waves (less energy)Structure and - Numerous lines of - No crackscomposition of weakness - Hard rockscoastal rocks - Soft rocksPosition of the - Open coast - Protected andcoast sheltered by 8 structures
Waves can be destructive or constructive..1. Destructive waves:• operate in storm conditions• arecreated from big, strong waves when the wind is strong and has been blowing for a long time• occurwhen wave energy is high and the wave has traveled for a long time• tendto remove material from the coast and associated with erosion• backwash is stronger than the swash.
2. Constructive waves:• operate in calm weather• are less powerful waves• break on the shore and tend to deposit material, building up beaches• are responsible for transporting material .• swash is stronger than the backwash.
HYDRAULIC ACTION• Direct impact of the waves against the coast. Compress air and exert pressure in the cracks of rocks (pg 92)• Enlarges lines of weaknesses after repeated crashes of waves• Cavitation: water surges into cracks, joints, faults. Results in compressed air and builds pressure. Water retreat releases pressure and trapped air which breaks the rock up. 13
The constant force ofwaves crashing on theshore damages it. This is called hydraulic action.
CORRASION/ABRASION • Impact of the materials carried by the waves scraping against the coast • Turbulence of the currents produce a scouring effect • Chiselling effect / grinding action on the coast • Cutting and breaking the rocks on the coasts 15
ATTRITION• Rocks rub or hit against each other, breaks down into small round smooth pieces(pg 93)• Materials from the waves collide with materials on the coast• Impact causes materials to break into smaller pieces which becomes sand 16
SOLUTION/CORROSION • Waves react chemically with soluble minerals in the rocks and dissolve them (pg 93) • Corrosion of rocks by seawater • Wave action increases the rate of reaction by removing the reacted chemical solution • Eg limestone 17
• Coastswhere the geology alternatesbetween strata (or bands) of hard rocksand soft rocks is called a discordantcoastline.• Discordant coastlines will have alternatingheadlands and bays.• Concordant coastline is where the rockremains the same along the coastline.• Concordant coastlines tend to have lessbays and headlands.
• Alongthe coastline of the Isle of Purbeck in Dorset (south coast of England), there are both discordant and concordant coasts.• Thediscordant coast has been formed into Studland Bay (soft rock), Ballard Point (hard rock), Swanage Bay (soft rock) and Durlston Head (hard rock).• AfterDurlston Head the rock remains hard. This concordant coast has less features.
Coastal features Created by erosionAlong a coastline there are often many features created by erosion. The most common of these are: 1.Cliffs 2.Headlands and Bays 3.Caves 4.Arches 5.Stacks 6.Stumps
COASTAL LANDFORMS FORMED BY WAVE/MARINE EROSION: SEA CAVES, ARCHES, STACKS AND STUMPS(C) Sea caves, arches, stacks and stumps1. Sea caves – a tunnel-like opening at the base of the cliff.2. Erosional processes such as hydraulic action, abrasion and corrosion by destructive waves act at the base of a cliff/headland along a line of weakness in the rock to form a hole called a notch.3. Continual erosion enlarging the notch to form a cave.4. Prolonged wave erosion enlarges and lengthens a sea cave until it finally cuts right through the headland and form an arch.5. Further erosion of the arch causes it to collapse and an isolated pillar of rock called a stack is formed.6. The stack can be further eroded and weathered. It is finally worn down to a stump which is covered during high tide.
1. Cliffs • One of the most common features of the coastline in Britain and around the world are cliffs.• Cliffs are shaped through a combination of erosion and weathering. The weather attacks the cliff top. The waves attack the cliff foot, causing a wave-cut notch at the bottom.• Soft rock erodes easily and creates gently sloping cliffs. Hard rock is more resistant and erodes slowly and creates steep cliffs.
Sea cliffs A tall, steep rock face, formed by the undercutting action of the seaSeven Sisters chalk cliffs on the East Sussex coast
Wave-cut notchesA rock recess at the foot of a sea cliff where the energy of waves is concentrated
The formation of sea cliff and wave-cut platform
2. Headlands and bays• Headlands are formed when the sea attacks a section of coast consisting of alternating bands of hard and soft rock.• Thebands of soft rock, such as sand and clay, erode more quickly than those of more resistant hard rock, such as chalk.• Thisleaves a section of land jutting out into the sea; this is called a headland.• Theareas where the soft rock has eroded away, next to the headland, are called bays.
Erosion can create caves, arches and stacks along a headland. Again weathering can also help to create these landforms. 3- Caves occur when the waves force their way into cracks in the cliff face. The water contains sand and other materials that help to grind away at the rock until the cracks become a cave.4- If the cave is formed in a headland, it may eventually break through forming an arch.5- The arch will gradually become bigger and bigger until it can no longer support the top of the arch. When the arch collapses, it leaves the headland on one side and a stack (a tall column of rock) on the other.
Old cliff line Original Land su rface stack stump Natural Wave-cut platform Arch