To what extent are coastal landforms products to marine processes?

By Raya Racheva 5IB

The coast is the boundary on the ocean where the land, sea and air meet and interact with each other, and influenced by the human activity shape the diverse, ever changing forms of the coastal terrain. The various processes that act on the coastline, like terrestrial, atmospheric, marine and human impact, make it impossible for the landforms to resemble. Even though each of the factors mentioned above are present at all time and they all have their part in the development of the coastal landforms, this essay will look at how big is the role of the marine processes in specific and are there other factors that can be considered as mostly acting on the coasts.

On the coastal terrain, from the zone where the salt spray, sea water and sand blown by the wind towards the inland extend, to the place on the sea bed to which waves can move sediment, the landforms are defined into different types. Rocky shores, coastal wetlands, sandy beaches, coral reefs are all products of the constant actions of water, humans, and atmosphere. In addition one of the four processes listed above might have a bigger impact on a coastal landform than the others.

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Waves, currents, tides, salt sprays and some biotic features like corals are all known as marine processes. The waves supply a huge amount of energy that results erosion of the land and the deposition of the eroded sediment on the coast. Formed by the friction between the wind and the surface of the water, the wind waves that are in deep sea are waves of oscillation and the ones that are in shallow water are waves of transition. The energy of a wave is determined by its height and period. Powerful waves like the swell are generated by long fetched wind (wind that blows over large distances), which makes them travel freely with long period and length and low height and steepness. When the waves reach a headland while travelling towards the shoreline (the boundary of land and sea), this is where the shallow seabed slows them down, and then they are refracted around the headland (fig. 1). Those waves concentrate most of their energy on the headland, eroding it and constructing cliffs, and when they meet the bay with less energy they deposit the sediments, forming beaches. Tombolos, like Howth head in Dublin, Ireland, are also formed the same way: when the waves are refracted by an island near by the coastline, they meet behind it, carrying sediment which is deposited there, and eventually the island becomes connected to the mainland (fig. 2). These features distinguish two types of waves- destructive and constructive.

Marine processes have big role in the formation of depositional and erosional landforms as they depend on the energy of the waves and sediment brought by the sea and rivers available. The destructive waves of high energy and the constructive waves of low energy help shape not only beaches and tombolos as explained above, but also a variety of other depositional landforms like spits, bay-bars, off-shore bars, sand dunes, salt marshes, deltas, barrier islands.

Spits are formed when sediments moved along the coast by the swash and backwash of the waves (the longshore drift) are deposited in linear form with one side attached to the land, usually across a river mouth (fig. 3). If a river current does not interrupt the building of these deposits, the spit can reach other part of the coast, connect to it and form a bar (fig. 4). Storm waves throw heavier material above the high-water mark, which makes the spits or bars more permanent. Such actions have formed the Chesil Beach on the Lyme Bay on the South coast of the UK.

Even though the waves with their energy have a big part in the shaping of land, other factors must also be taken into account when explaining how are the various types of coasts formed. When erosion is happening the types of rock that the waves act on have also impact on the way the coast will look like. Harder rock like limestone will make it difficult for the water to erode it, whereas the soft sandstone is easier to brake. The concordant and discordant position of the rocks is also important. The discordant arrangement of rocks will lead to the formation of headlands where the harder rock is, and bays will appear where the softer rock has been eroded (fig. 5). This makes the geology of the coast a very important feature along with the other terrestrial processes like weathering e.g. honeycomb weathering, tectonic movements and biotic features. They are on the other hand also interconnected with the atmospheric processes like gravity, solar energy and climate, and the human activity.

The gravity of the sun and the moon is the reason for the tides that form on earth; the waves are formed not only by the wind on the surface of the water, but also by tectonic movements; submerged landforms like rias, dalmation coast and fjords, and emerged landforms like raised beaches are all created by sea-level changes, which are consequences of the ever changing climate; the protection walls built perpendicular to the shoreline with the intention to protect the land from erosion actually denature the coast forming beaches that would not naturally appear without these conditions. These facts lead to the conclusion that the processes responsible for the landscaping are all interrelated. Marine processes cannot occur without the presence of the atmospheric and terrestrial features and the impact of human activity on the coasts is inevitable. In addition, even though each process has its own part in the constructing of coastal landforms, their great interdependence makes it hard to conclude the extent to which either one of them is most important.