This is a simple EarchCache at a lovely location however it is on and around very uneven and sometimes slippery surfaces.
It might be possible to stay on the promenade and gather the info needed so I have graded the terrain as T1
Please visit the location, taking great care.
You will need to make some observations, gather some information and either message or email the answers to me.
Please feel free to log your find and send your answers at the same time.
Geology and geomorphology
Limestone pavement is a habitat with a high geological interest. Forms of limestone pavement can be found in many places in the world, especially in Alpine and Mediterranean areas, but these lack the distinctive surface patterning seen on British pavements.
How limestone pavements form
Limestone is a hard sedimentary rock consisting of calcium carbonate, formed by the deposition of plant and animal remains on the sea floor and is thus known as a calcareous rock. Limestones often contain the visible remains (fossils) of shells and corals. As limestone is a sedimentary rock, it is laid down in layers or ‘beds’ separated by ‘bedding planes’ which are caused by changes in deposition rates or content of material deposited. Limestone pavements in England, Wales and Ireland are mainly formed on deep beds of Carboniferous limestones which were deposited about 350 million years ago.
In this location you will notice that the bedding planes are well separated, in fact there are some places where the depth of the pavement is such that there are no bedding planes at all above ‘ground’ level. Get down and look into the cracks and observe the bedding planes, there will be a question about this.
The formation of limestone pavements in the UK and Ireland began with the scouring of the limestone by kilometre thick glaciers during the last ice age. The weight of the ice removed the soil that lay over the limestone, and also fractured the limestone along existing horizontal surfaces of weakness known as bedding planes. Fractured rocks were stripped away leaving level platforms of limestone on which a thick layer of boulder clay (glacial till) was deposited as the glaciers retreated.
Wind blown material was then deposited on top of the boulder clay. This external material is particularly important for soil formation, as limestone does not weather down into soil which would mean if there had been no glacial deposits, there would have been no soil development. From the flat limestone surfaces, the characteristic features of limestone pavement have been formed by water in the glacially deposited soil exploiting cracks and fissures in the rock such as bedding planes and joints (lines of weakness in the rock generally running at 90o to bedding planes).
Karst scenery
Limestone pavement is a type of karst landform. Karst is the word for an area of soluble rock in which the landforms are of a solutional nature (i.e. they are caused by water dissolving the rock ) where drainage is usually underground through rock fissures rather than in surface streams. Karst, a term originating from a limestone region in the former Yugoslavia, is derived from the Slovenian word kras, meaning a bleak, waterless place. It is used to describe a landscape containing erosional features such as bare pavements, subterranean water systems, dry valleys, dolines which are small to medium sized closed depressions with no surface outlet for water (hundreds of metres in diameter and tens of metres deep); and poljes which are large depressions with diameters of 1km upwards and depths of over 50m or so.
It is the layer of debris left by the retreating glaciers and also by wind deposits that hold the key to the development of the characteristic limestone pavement landforms over the last 10,000 years. The karst landforms were formed by the gradual dissolving of the limestone by mildly acidic water seeping through the forest cover which had become established on the soil above the limestone platforms. If this glacial debris had not been in position, then the weathering processes that form limestone pavements could not have taken place.
Clints and Grikes
Due to the solubility of limestone, limestone pavements are associated with some very curious and unusual landforms. The most characteristic surface feature of limestone pavements is their division into blocks, called clints, bounded by deep vertical fissures known as grikes. Clints and grikes form under relatively deep cover of soil where water, carrying carbonic acid which is formed from dissolved carbon dioxide as well as organic acids from decaying vegetation, picks out vertical lines of weakness (joints) in the rock. These fissures widen over the years as the acidic water preferentially attacks the lines of weakness. Grikes take many thousands of years to form under the soil as the rate of solution is slow.
Over time, the soil on the top of the limestone platform began to disappear down the newly eroded grikes, and was gradually eroded from the tops of the platforms. Some of the material lost into the grikes was washed deep into the drainage systems of the limestone pavements through connecting fissures, leaving open grikes of a metre or more in depth. These erosional processes were increased when forest clearance and grazing was introduced by humans onto the buried pavements leading to a more rapid exposure of pavements.
Runnels, Pits and Pans As well as clints and grikes, limestone pavements also have a number of characteristic surface formations. These are known as runnels, pits and pans and take different forms depending on the structure of the pavement on which they form.
Runnels are gutter-like channels eroded out of the surface of the limestone which drain into grikes. The formation of runnels takes place under a shallow layer of soil. Runnels formed on steeply sloping limestone are usually close together and parallel, whereas runnels forming on gentle slopes take dendritic or branched forms which can be looked at as a miniature river system.
Pits and pans are small scale solution features (i.e. formed by water and acids dissolving the limestone) found on the tops of clints. Pits are deep and free draining into the subterranean limestone drainage system. Pans are shallow, have an impervious base and hold water. Both of these features also form under shallow soil cover. Some research indicates that the deeper features can be formed by humic acid from the root balls of trees resting against the limestone and dissolving it into the characteristic round bottomed features of pits and pans.
When solution features on a limestone pavement are exposed due to soil loss, they become more weathered and ‘sharper’ in appearance. It is possible to differentiate newly exposed pavement from pavement which has been exposed for longer periods of time by looking at the sharpness
At this location it is a little difficult to spot the top of the pavement because being so close to the sea there has been significant erosion over and above what other pavements have suffered. This outcrop is the remains of a pavement which is surrounded by the sand and heath which is sometimes covered by the tide.
There is another larger outcrop just North East of the location given at GC1ND87
Questions for the smooth pavement
1) Please describe the pavement at this location, concentrate on the top of the pavement and the depth of the clints and grikes
2) Please explain why this section of limestone pavements does not have a flat pavement like surface.
3) Just below the steps is the outcrop you are looking at, please tell me how far from the promenade it extends and how wide the outcrop is.
Thanks for attempting this EarthCache
treboR