Cliffs are giant land masses of rocks and sediments that rise at an almost a 90° angle
Cliffs are giant land masses of rocks and sediments that rise at an almost a 90° angle. They are commonly formed near waterfalls, oceans, valleys and high up in mountains, due to processes such as erosion and weathering. Weathering play a vital role in the formation of cliffs. This process is stated to be of natural events which break down pieces of rocks to give the coastline its shape. These natural events include wind or rain, freeze thaw and salt crystallisation which have minimal effects on the cliffs at a short period of time whereas colossal hazards/ events such as hurricanes and storms can have a dramatic effect of the erosion rate at cliffs. May, (1971), remarked that the most substantial losses occurred in winter where rainfall and winds were at their peak. In coastal areas such as Dorset, which is both concordant, immense winds and waves of long fetches break off soft or less resistant material and rocks which leaves the more resistant rocks exposed therefore channelling the formation on cliffs demonstrated at the Cliffs of Moher, County Clare, Ireland. The definition of a concordant coast is when coastline has alternating layers of hard rock and soft rock that run parallel to the coast. The soft rock in usually protected from erosion as the hard rock acts as a protective barrier. Landforms such as Coves can be formed if the hard rock has been ruptured through therefore leaving the soft rock exposed to erosion (e.g. Lulworth Cove).
Furthermore, previous coastal studies carried out by Johonnessen et al (1982) concluded that heat of salts on salt crystallisation was possibly the main erosive mechanism above high tide on sunny, south facing sandstone cliffs for example east cliff. The average surface reading of NaCl are 27ppm (De Wolf, 2001). This study was constructed in Brighton therefore results will approximately be similar in Dorset.
Many studies have been carried out to investigate what factors put certain cliffs at risk of rapid erosion. A variation of cliff response occurs according to material strength. Hard rock coasts erode very slowly due to the constraining factors of material strength and rock mechanics (ALLISON, 1989). Therefore the more resistant rock cliffs should remain essentially stable when erosional processes act upon them. In contrast, soft rock cliffs are subject to additional weakening by weathering and degradation by mass movement; these processes are likely to operate more rapidly in the wetter, warmer climate predicted for regions such as Southern England due to global warming (Department of the Environment, 1991). This concluded conclusively that the cliffs present in the south of England are more susceptible to erosional/ weathering processes. (Richard and Lorriman, 1987) pointed out that higher cliffs erode more rapidly because they generate higher shear stresses and suffer larger landslides, however they also yields more sediment per unit of recession. Whilst reading the article on BBC news ‘UK storms: Extreme weather caused years of erosion’ (21 February 2014) an interesting fact caught my attention which stated “more than 3m of the cliff at Birling Gap has been lost to the sea this year”. This is where I felt that a wider range of studies can be beneficial to investigate the reasons why this unpredictable event occurred, and also encouraging more people to undergo investigations to arrive at reliable conclusion.
I have chosen these two locations as they show several significant differences such as geology, coastal landforms, wave type etc., which will allow me to compare and contrast and determine which factors are the most significant which contribute to cliff erosion.
The title of my investigation is “To what extent is lithology the predominate factor which contributes to rapid erosion at the cliffs at Weymouth”
In the planning stage I split this title into 3 other research question/ sub questions; (1) “To what extent do wave characteristics contribute to rapid erosion on the cliffs at Weymouth?”, (2) “To what extent do geological features such as faults and bedding planes (lithology) contribute to rapid erosion on the cliffs at Weymouth?” and finally, (3) “sub-aerial processes can be viewed as an vital factor but how significant is their contribution to cliff recession?”
• For sub-question (1) I would expect to find as wave speed and wave frequency increases (destructive waves) the rate of erosion at the cliffs will be significantly higher than coastlines with low energy for example Holderness coast. This is due Weymouth being a high energy coastline which therefore means that destructive waves will be the most foremost wave, causing the cliffs to erode and recede at a higher rate. In addition I expect the cliffs at west bay to erode significantly faster than the cliffs present at Lulworth, due to geology characteristic.
• For sub-question (2) I expect lithology to be a major contributor to rapid erosion. Feature such as faults and bedding planes can determine whether a coastline is susceptible to erosion or firmly resistant to erosion. This therefore implies that these features also determine the shape of a coastline and what landforms can be created.
• For sub-question (3) i expect that gathering primary results for sub aerial processes on their contribution to cliff erosion will be quite difficult as precipitation and strong wind will be minimal during the time in which in investigation was constructed. However background research and secondary results will be carried out to enhance the knowledge of the subject area. This will be done by reading information from a supplied geography booklet that will contain geographical literature, which will help me determine is sub-aerial processes are a significant contributor to cliff erosion.