Friday, August 23, 2019

Cliff erosion and saltmarsh Assignment Example | Topics and Well Written Essays - 1000 words

Cliff erosion and saltmarsh - Assignment Example Cliff erosion or cliff retreat in particular has vast economical effects on property by indirectly playing part in land sliding. However, the eroded land is deposited somewhere else and they are in turn responsible for indirect creation of salt marshes. The paper will take a look at the process of cliff erosion along with the development of salt marshes at North Norfolk. The major processes involved are discussed in detail; 2. Cliff Erosion The Hunstanton cliffs in North Norfolk are considered as an example and a case for cliff erosion. They have a length of approximately three kilometers and a maximum height of 18 meters . The cliffs are composed of weak rock or chalk in particular. They are inclined at an angle of 60 degrees. The cliffs have retreated almost 30 meters in 127 years of observation. The major cause of Cliff Erosion is the cutting action of the waves. The waves come in contact with the lower base of the cliffs and move the base material by cutting away rocks. The process is accelerated by presence of cracks in rocks which assist in erosion and even weathering. Once the base is undercut, the cliff becomes unstable and the structure above sea level crashes. The rate of erosion depends on the angle at which the waves collide with the cliffs. In case of the Hunstanton cliffs, the waves run parallel to the cliffs. Rise in sea levels is a major concern for cliff erosions. It is estimated that by the year 2020, the sea levels can rise as much as 29 centimeters (Pethick, 1993). Global warming has accelerated the rate and the rise has serious consequences not only for islands but present indirect threat to settlements near cliffs. The effect reinforces the actions by tides and contributes towards erosion. Furthermore, this rise effects the embankments and in particular the estuaries. 2.3 Tectonic Activity A possible explanation for cliff failure for chalk based structures were pre existing cracks by tectonic activity (Mortimore and Duperret, 2004). The theory was presented by Mortimore in 1979 and relies on the concept that the cliff structures have cracks and fractures that were induced by tectonic activity in the region. The fractures make the cliffs unstable and vulnerable to the effects of erosion or weathering. Furthermore, tectonic activity has been linked to the effects of rising sea level. The crust changed its height over time and in turn the mean surface level decreased (Pethick, 1993). 3. Salt Marshes The North Norfolk coast has developed almost 12 distinct salt marshes over a period of 2000 years (Pethick, 1980). The area has seen development of marshes along the coastline as well as some area housing marshes inland. These marshes are spread across the length of 30 kilometers and therefore, experience almost similar tidal conditions. Some of the reasons for development of these marshes are discussed in detail; 3.1 Tidal Activity Tides are the main carrier for material and factor for development of salt marshes. Tides deliver material which can grow in sea water and sediments are continuously fed to the area. Marshes change over time and their geographical properties depend mainly on tidal activity. The low tides give an opportunity for the marsh to grow and the high tides deliver minerals from the surrounding areas. These are generally found in spits and embankme nts. Developing marshes however, are at sandy environments near the coastline. The mature marshes are covered for almost 7 to 10 hours in a single lunar cycle (Stoddart, Reed and French, 1989). If the marshes are

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