Coasts Revision Notes - AQA Geography
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Introduction
Coasts Revision Notes ? AQA Geography 1. Spring and Neap Tides Spring vs. Neap Tides Spring tides occur when the Earth, Sun and the Moon are all about in the same line. This causes the highest tidal range due to the strongest gravitational pulls with the high tides being the largest and the low tides being the smallest. Neap tides occur when the Earth, Sun and Moon are at 90 degrees which causes the gravitational pull to be less effective. This produces the lowest tidal range of tides. 1. Coastal Transport Long shore drift transports material along the coast. In the UK, the prevailing wind blows from the South West causing the waves to approach the southern coast at an angle of 45 degrees. Therefore material moves from the west to the east. The swash of the wave carries the material up to the beach at this angle. The bed load is moved along by rolling by traction however pebbles are lifted and bounced along the floor in a leap frog action ? this is saltation. ...read more.
Middle
When the waves hit the coastline, they are refracted and they tend to ?bend? round the headland, into lower energy waves. These waves then deposit sediment and beaches eventually build up. Case Study: Purbeck coast, Dorset. The Eastern side is discordant. Headland ? The foreland Purbeck Coast, Dorest. Geology ? Chalk (made millions of years ago from Coccoliths). This headland is 1.3km wide. Bay ? Swanage Bay made from Wealden & Purbeck bed clays. This bay is 2.5 km wide. 1. Causes of cliff collapse Coastal Reasons * When waves head towards the coastline and the sea gets shallower, friction in the bed slows the bottom of the waves and make them more elliptical. The crest of the wave rises and then it collapses. * Destructive waves are high frequency, and are high and deep. They are around 10-14 waves per minute and their strong backwash removes material. * The waves break at the base of the cliff where the wave energy is concentrated. ...read more.
Conclusion
Sub-Arial * Not directly linked to sea, but from land * Freeze Thaw ? When the diurnal range is around 0 dregrees ? Scottish Highlands ? Water expands by around 9%. Fluccutations in pressure fragments of rock may break off. * Biological - Rabbits may burrow into the cliff and piddocks may also weaken the rock which may remove some of the rock. * Chemical weathering, CO2 found in rainwater may form carbonic acid when it rains ? attacks the calcium carbonate such as in limestone. Mass Movement * Slumping ? Rainfall infiltrates the soil, making it heaver. * The material moves downhill, leaving a exposed scarp face * Case Study ? Holbeck Hall, Scarborough. * 1993 ? dry weather cracked the clay. This made the rock impermeable due to hot dry conditions * Next two months 140mm of rain fell (prolonged rainfall) * This then therefore infiltrated the soft rock above, but lubricated the clay. * On 3rd of June ? the land was slipping into sea at 3m per hour. Collapse of hotel. Rest of hotel had to be demolished and they owners sued the authority ?breach of its duty and care?. ...read more.
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