Factors affecting the rate of Erosion Lesson aim : To examine the different factors affecting the rate of coastal erosion Lesson objectives: What influence do waves have on coastal erosion? How does depth of sea, fetch etc. influence the rate of coastal erosion? What role does sediment and beach width play? How does the geology of an area affect the speed of coastal erosion?

Set out your notes today in a simple table like the one below Set out your notes today in a simple table like the one below. (you will see why as the lesson evolves!) Key Influence / Factor affecting the rate of erosion Image (s) to support

Breaking Point of a wave A wave which breaks as it hits the foot of the cliff releases most energy and causes maximum erosion. If the wave hits the cliff before it breaks, then much less energy is transmitted whereas a wave breaking further offshore will have had its energy dissipated as it travelled across the beach.

Wave Steepness Very steep destructive waves formed locally (sea waves – where there is a mixture of both short wave length and long wave length peaks produced by a storm) have more energy and erosive power than gentle constructive waves formed many kilometers away (swell waves – occur where a storm produces waves a large distance from the shore and gives time for the waves to ‘sort’ themselves into similar velocities as they approach the shore).

Depth of Sea, length and direction of fetch, configuration of coastline. A steeply shelving beach creates higher and steeper waves than one with a more gentle gradient. The longer the fetch, the greater the time available for waves to collect energy from the wind. The existence of headlands and vertical cliffs tends to concentrate energy by wave refraction.

Supply of Beach Material Although a continual supply of material is needed to erode the coast, an surfeit (excess) of material can protect the coast by absorbing wave energy.

Beach Width Cliffs containing a readily available supply of sand (eg north Norfolk) will form wider beaches than those with limited amounts ( eg Folkestone Warren / Holderness). The wider the beach, the greater will be the loss of energy (waves take longer to pass over it and more energy is lost by friction) and the slower the rate of coastal erosion.

Rock Resistance The strength of coastal rocks influences the rate of erosion. In Britain, it is coastal areas where glacial till was deposited at the end of the last ice age (10,000 years ago) which are being worn back most rapidly (eg Holderness). When Surtsey (Iceland) rose out of the sea in 1963, it consisted of unconsolidated volcanic ash. It was only when the ash was covered and protected by a lava flow the following year, that the island’s survival was seemingly guaranteed.

Rock structure and Dip Rocks which are well-jointed or have been subject to faulting have an increased vulnerability to erosion. The steepest cliffs are usually where a rock is horizontally (deep overhangs / notches may develop eg. Flamborough Head, north Holderness, Yorkshire) or vertically bedded (eg. Lands’ End / Northern Ireland – Giants’ Causeway). The gentlest cliffs are usually where the rock dips upwards away from the sea. Blocks break off and slide down the cliff face. Erosion is also rapid where rocks of different resistance overlie one another eg. Chalk and Gault Clay at Folkestone Warren.

Activity: Make a copy of figure 3.10 from page 91 to support your notes. Homework: Use Google images to collect a number of different images to support your notes. Stick these in the right hand column of your table.