Cliff erosion and saltmarsh - Assignment Example

? CLIFF EROSION AND SALTMARSH by ----- Academia Research Introduction Coastlines are eroded over time by tidal activity. Furthermore, the waves incorporate forces from different factors and deliver their force directly to the coastline. Besides the physical impact, the process is reinforced by physical and chemical weathering. Cliff erosion or cliff retreat in particular has vast economical effects on property by indirectly playing part in land sliding (Komar, 1998). 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 (Drake and Phipps, 2007). 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. 2.1 Undercutting/Toe Erosion 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 process is called undercutting or toe erosion (Bridge and Demicco, 2008). 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 (Drake and Phipps, 2007). 2.2 Rising Sea Level 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 embankments. 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 submerged for a longer period it can affect their growth and even survivability. 3.2 Rising Sea Level Sea level is the major factor for development of marshes. The tidal activity occurs in cycles whereas the risingsea level poses permanent threat to salt marshes. The marshes in particular near the coastline if submerged cannot sustain themselves. The effect of low tide is decreased as relevant to creation of developing marshes, whereas, for mature marshes this rise in sea level means permanent submersion of spits and embankments for longer durations. 4. Link between Cliff Erosion and Salt Marshes The simplest explanation that links the two phenomena is described to be the eroded land carried by the sea currents along the coastline towards the marshes in the east. The deposits mainly consist of sand and fine grain particles. These are broken down by colliding with each other by the waves or the process called attrition. The erosion takes away nearly 3000 cubic meters of land per year for every kilometer from the Hunstanton cliffs (Drake and Phipps, 2007). The sea waves run parallel to the coastline which is southeast; however, the observations partly coincide with the idea that the eroded mass is transported towards the eastern marshes. The western area of the Norfolk coast has seen sedimentation and development in marshes (May, 2003). These observations raise questions about the direction of mean sea current. Besides this simple transportation of land mass, marsh developments have been observed and a relation between cliff erosion with salt marsh developments has been established on the basis of tides. The highest level of tides known as Spring Tides accelerates cliff erosion process with increased contact with the cliff interface. These tides can in turn fill up the estuary and reach mature marsh areas relatively inland. A relation has been made with the velocity of the tide and sedimentation process. Spring tides deliver sediments to mature as well as developing marshes simultaneously; however, the sedimentation rate is greater at developing rather than the mature marshes (Stoddart, Reed and French, 1989). This is due to the simple fact that coastlines are submerged deeply at spring tides and have more opportunity for sedimentation. The elevation increase for developing marshes is greater than the mature marshes and this rate coincides with the tidal patterns. These patterns are shown to vary with long term year cycles of almost 18.6 years (Adam, 1990). Furthermore, the process is supported by the rise in sea levels. The two phenomena are related with changing sea levels. Higher tides mean higher erosion as well as higher sedimentation rate for the marshes. 5. Conclusion North Norfolk has been a major observation site for cliff recession studies. The site is monitored for over a century and provides scientists an opportunity to compare data that is reliable and based on ground observations. Studies have sparked debate regarding the phenomena of cliff erosion along with salt marsh developments. Wave actions along with tidal activity are considered as the main causes supported by rise in sea levels. Patterns of sedimentation are not always constant but the area provides an interesting opportunity to look into the matter and learn about these phenomena. Furthermore, the tectonic activity and the resulting rise in sea levels for the area also gives us a peek into the possible effects of global warming associated with rising sea levels in the future. References Drake, A. and Phipps, P., 2007. Cliff Recession and Behaviour Studies, Hunstanton, UK. Maritime Engineering, 160(3), pp.3-17. Komar, P., 1998. The Pacific Northwest Coast: Living with the Shores of Oregon and Washington. North Carolina: Duke University Press. Bridge, J. and Demicco, R., 2008. Earth Surface Processes, Landforms and Sediment Deposits. Cambridge: Cambridge University Press. Pethick, J., 1993. Shoreline Adjustments and Coastal Management: Physical and Biological Processes Under Accelerated Sea-Level Rise. The Geographical Journal, 159, pp.162-8. Mortimore, R. and Duperret, A. eds., 2004. Coastal Chalk Cliff Instability. Bath: The Geological Society. Pethick, J., 1980. Salt-Marsh Initiation During the Holocene Transgression: The Example of the North Norfolk Marshes, England. Journal of Biogeography, 7. pp.1-9. Stoddart, D., Reed, D. and French, J., 1989. Understanding Salt-Marsh Accretion, Scolt Head Island, Norfolk, England. Estuaries, 12(4). pp.228-236. May, V., 2003. Coastal Geomorphology of Great Britain. Geological Conservation Review, [pdf] Available at; [Accessed 5 May 2012]. Adam, P., 1990. Saltmarsh Ecology. Cambridge: Cambridge University Press. Read More