How Natural Processes Operate at Coastal Geographic Environment.
...ach other causing the base of the headland to erode. Chemical Erosion/Corrosion occurs due to the content of limestone in the rockface of Otakamiro point. The seawater combined with the limestone produces a weak chemical solution, which erodes the base of the cliff and produces a pitted effect. Chemical Weathering is when water weakens the structure of the rock and Mechanical Weathering is where water seeps into the rock face causing fragments of rock to break off. These types of erosion have caused the formation of several phenomena at Muriwai. Motutara Island (stack) was produced by the formation of two caves on either side of the headland – forming an arch and the roof slowly eroding away due to vertical erosion. Fisherman’s Rock was produced by cliff retreat when undercutting stones are thrust at the cliff by wave action. The blowhole was formed by vertical, hydraulic and mechanical erosion causing the cracks and fissures to enlarge over time to produce this hole. Types of wave erosion operating on the headland have produced the cave. Wave Refraction is an important process as it influences wave erosion on Otakamiro headland and on the beach at Muriwai (refer to Diagram 1). Wave Transportation (Longshore Drift) varies spatially due to wave refraction. It is the process by which waves alter their course as they interact in shallow water with the seabed along the coastline. This process produces wave erosion, which focuses its energy on Otakamiro Point. Diagram 1 Constructive, Destructive and Dissipative are the types of waves that operate at Muriwai that cause erosion. Dissipative waves are the waves usually found at Muriwai – they lose their energy before they reach the shore as they usually break on the offshore bar. Constructive waves are long waves with little height that leave material at the top of the beach, building it up. Destructive waves are erosive and carry material seawards. Wind Erosion is the driving mechanism for Coastal Transportation and Coastal Deposition. Strong winds have a better ability to cause erosion at Muriwai’s Coastal Geographic Environment. Wind erosion is most effective on well-drained landforms such as sand dunes. Loose particles are more easily eroded than wet heavy soil, sand and rock. Coastal Transportation is the movement of sediment and sand by waves and wind. Drifts, currents, sea level changes and the wave types also control it. There are two main types of Coastal Transportation – theses are Wave Transportation and Wind Transportation. Longshore Drift is a transportational process, which determines the shape of Muriwai. Longshore drift occurs as a result of wave action. Driven by the prevailing southwest winds the wave (swash) hits the beach and moves sediment sideways up the shore and the backwash returns the sediment at right angles. The following waves repeat this process and as a result the sediment gradually moves along the shore in a ‘sawtooth motion’ called Longshore Drift (refer to Diagram 2). Longshore Drift is the main way that sediment is moved from Otakamiro Headland to create the beach, leaving more erosion to take place on Otakamiro Point. As this is a natural process it disrupts human activities and may occur to the poin...