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Thread: Coastal erosion question

  1. #1 Coastal erosion question 
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    ...I was crossing the English channel between Dover and Calais recently, ( a distance of 22 miles, for those not familiar with local UK geography ), and got to wondering.....How is it possible that the 'White cliffs of Dover', hundreds of feet high, could have been eroded to their present position in less than 12,000 years, when, due to the last Ice age, the English Channel did not exist, and the land from Southern England to Northern France was, presumably, untouched by coastal erosion.
    Is it possible for such a large amount of erosion to take place in such a short time?...or had a lot of the erosion taken place prior to the Ice age?


    jrey
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  3. #2  
    Universal Mind John Galt's Avatar
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    I am not sure of the details, but remember that some of the effect has been due to simple flooding of low lying land as the ice caps melted. Sea levels rose by a few hundred feet as a result (and the Channel is not deep). If we assume, for sake of argument, that one third of the distance was dealt with by flooding, not erosion we are left with fourteen miles to account for. That is roughly 70,000 feet. So we are looking at erosion rates of around six feet per year.
    Erosion rates determined over the last 125 years average 2.5 feet per year. That is the same order of magnitude. We only need to envisage higher rates of erosion at times of greater tidal scour when the channel was narrower and we have the solution.


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    I am not familiar with the geography of this area, however, 12,000 years ago we would have been the quaturnary, a period known for land-shaping from glacial processes. the white cliffs of dover, are chalk beds aren't they?? which means they can be very easily eroded as its a very soft material. The area mentioned im assuming, was ice loaded, and glaciers would have been moving toward the sea, eroding much of the landscape in its path, possibly truncating much of the beds. however, if these are chalk beds, they would have been easily eroded more recently, by rain, waves, etc.
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    Don't think ice reached as far south as Southern England, but in Scotland it would probably be a couple of kilometers thick, - very heavy. Scotland was pushed down under the weight of ice and Southern England conversely was raised up, like a plank of timber see-sawing. Of course now the ice is gone Scotland is 'floating' back up and pushing Southern England down. How this might impact erosion apart from possibly lowering the seabed off English South coast I don't know unless maybe cliffs were eroded early in the ice-age by a receding sea as the cliffs rose up under the weight of growing Scottish ice. In which case the later dried out land bridge from France to England would have been flat until you reached England where you would be suddenly be faced with the white cliffs of Dover. Hmm ...maybe archeology could help by finding the first settled areas in Southern England, Folkestone, Dover or Deal...
    I am just speculating and hope I'm not going to confuse you. ..
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  7. #6  
    WYSIWYG Moderator marnixR's Avatar
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    from wikipedia :

    "During an earlier glacial maximum, the combined rivers had been blocked to the north by an ice dam; they filled a vast lake with freshwater glacial melt on the bed of what is now the North Sea. A gently upfolding chalk ridge linking the Weald of Kent and Artois, perhaps some thirty metres higher than the current sea level, contained the glacial lake at the Strait of Dover. At a certain time, and apparently more than once, the barrier failed or was overtopped, loosing a catastrophic flood that permanently separated Britain from the continent of Europe; a sonar study of the sea bed of the English Channel published in Nature, July 2007, revealed the discovery of unmistakable marks of a megaflood on the English Channel seabed: deeply-eroded channels and braided features have left the remnants of streamlined islands among deeply gouged channels where the collapse occurred."

    presumably this feature was (is?) still shallow enough to be uncovered by a substantial drop in sea level
    "Reality is that which, when you stop believing in it, doesn't go away." (Philip K. Dick)
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