Transcript Slide 1
Holderness case study The FASTEST ERODING COASTLINE in Europe Locally, rates of erosion have been up to 10-20m per year Holderness Coast is fastest eroding stretch of coastline in Europe – an average of 2 metres fall into the North Sea each year Over 30 villages have been lost since Roman times, erosion has been taking place for last 6000 yrs http://news.bbc.co.uk/1/hi/uk/7390654.stm The Holderness Coast is one of Europe's fastest eroding coastlines. The average annual rate of erosion is around 2 metres per year. This is around 2 million tonnes of material every year. Under lying the Holderness Coast is bedrock made up of Cretaceous Chalk. However, in most place this is covered by glacial till deposited over 18,000 years ago. It is this soft boulder clay that is being rapidly eroded. But what is the obvious question / learning objective??? WHY is it eroding so quickly? KEY REASON: it’s made of boulder clay – the most easily erodeable ‘rock’ (it’s not really a rock as it was deposited by the ice sheets in the last glaciation and has never then been buried and compressed and ‘turned to rock’ like chalk, sandstone, etc have) Notice the slumping... (subaerial process, happens on ‘soft rock’ coasts Less Resistant bolder clay cliffs near Mappleton Landslips: also known as rotational slumps, are occasional rapid movements of a mass of earth or rock dropping down along a concave plane. Water percolating through sandstone gets into the clay beneath, saturating it. With the weight of the rock above forcing down on it the clay moves seawards as a mud flow. With the clay moving sideways the sandstone above slumps down. Undercutting of a steep slope by the sea weakens the rock above, making a slump more likely. 13 Relatively long FETCH – dominant wind direction = from North East – so large waves Mappleton, Yorks. coast Groynes £10,000 each (wooden groynes) £1.5m each (rock groynes) What are they designed to do? Stop longshore drift Further down the coast this may mean that beaches are starved of sand and shingle Click here for video clip of Mappleton – where they built the rock groyne (£2m) to prevent prevent longshore longshore drift – but drift causing – but causing more erosion more further erosiondown further thedown coastthe – eg coast Cowden – eg Farm (Sue Cowden Earle) – as Farm the(Sue beach Earle) there – stopped as the beach getting there ‘fed’stopped with sand getting and ‘fed’ shingle with from sand further and North... shingle from further North... Mappleton and Holderness Coast Why??? Describe the effects of the erosion here. What would the knock on effects be? (classic 6-marker) So, over to you… Holderness: The FASTEST ERODING COASTLINE in Europe (1) Add labels to the map &/or photo to explain why it is eroding so quickly. Include at least these: cliffs = boulder clay, longshore drift, groyne, long fetch, North Sea, Mappleton village, thin beach (2) On A4 paper, try to write a sentence for each label explaining how it helps cause rapid erosion EXTENSION: Draw a spider diagram giving reasons why people still live on this coastline