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Tuesday, 9 July 2002 Monthly Meeting of the Essex Rock & Mineral Society Coastal
Landforms Report by: R Coleman
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Many of us never consider the geological implications of our landscape, mostly we either ignore it or go WOW!. Ken did an excellent job of trying to put the record straight in a very short time, by covering a few of the many aspects that control the Geomorphology (describing and interpreting the landscape). This is such a diverse subject that Ken concentrated on the processes that shape our coastline and how the nature of underlying geology dictates the results. The subject was divided into two sections, soft rock and hard rock. The major processes were described as: Erosion, Transportation & Deposition. Of these three, the talk was limited to the effects of erosion and then further restricted to the effects of "destructive wave" action. The classification of wave action is determined by the time interval between their arrival. Occurring at a rate of about 18 per minute and above, wave action is 'destructive' and has a distinctive type of turbulence. At lower rates the wave action becomes 'constructive' and has another characteristic style of turbulence. We were briefly introduced to the topic of transportation with the way currents are set up in the North Sea due to the prevailing wind and how this assist the erosion, transportation & deposition. The diagram of currents looked like a figure of eight. Ken applied the term Fetch when talking about these currents (don't ask me, I don't know. I always thought the currents were the effects of tides and the coriolis effect, all related to the spin of the Earth and the gravitational pull of the Moon and Sun, simple it is not! There are charts of tidal currents for the whole of the North Sea, which give the velocities at 1m above the seabed. This is all to do with the same subject, but it is worth remembering that Ken was discussing "destructive wave action only." Fetch is probably a term related to the wind. RC ) Next came a montage of excellent slides demonstrating all the various aspects of coastal erosion. Interestingly, (to me) were those taken at Walton back in the sixties. The rotational slumping at the Naze produced small ponds of trapped water at the rear of the slump, something that doesn't happen today. The explanation involves the rotation of the underlying clay forming in an impermeable trap at the back of the slump. (A few years ago, one of our members got trapped at the back of the slumped clay at Barton. I wondered at the time why this clay at the back was so boggy! Presumably some similar effect. It was a cold day and he carried on collecting minus his boots - eventually - after calling help for sometime - before being rescued! He was advised against venturing there. Oh! - you want to know his name do you? Derek Breden, specializing in collecting London Clay fauna from Ongar clay pits! He uttered those immortal words when first warned, "It's all right, I'm use to working in clay." Yes, we did laugh. RC) |
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The slides of the South West and the Pembroke Coast were magnificent, much of the folding in the rocks was attributed to the tectonics of the Variscan Orogeny. However, the superb exposed structures were due to the wave erosion. The controlling factors being the direction of the bedding and faults within the rock structures. Along some stretches of coastline the cliffs were undermined before toppling; in others, caves where developed along fault lines. As with all force, the path of least resistance was followed and developed to destruction. Ken went into some detail on the effects of wave action on chalk cliffs. He discussed the formation of multiple pier and inlet structures and how these are erode into arches and then needles. Sadly, structures the students of today have no opportunity of studying in this country, because of coastal defence work. In the talk, many other subsidiary erosion features were discussed like septarian nodules and other concretions erode on the foreshore. Many technical names were mentioned (like Lavatory Pan Rocks) along the way. Ken's experience of many years, combined with his fine collection of photographs taken over that time, provided us with a very brief look into Geomorphology. In this lecture there was only time to view a few of the his pictures (120 slides of the 240 brought along). It was an enjoyable talk but, to me, the people who have obviously gained most are those students who have been fortunate to have studied under Ken, a man that knows, loves, and communicates the subject par excellence! Fetch: Try this website: http://www.cao.bangor.ac.uk/staff/aje/lectures/prac_oc_5.pdf Subsequent to writing the above article I came across this reference for FETCH. The article is technical, I can follow the maths OK so it isn't that bad, but there is a paragraph that sums it all up rather nicely at the bottom of page 22. I assume you have the software for reading pdf files. RC |