Coasts

• Landscape systems, processes and change: Topic 2 focuses on coastal landscapes and change.
• Specialist concepts in landscape systems, processes and change include causality, equilibrium, feedback, interdependence, mitigation, adaptation, risk, resilience, systems, thresholds, and specification.
• Coastal landscapes develop due to the interaction of winds, waves and currents, as well as through the contribution of both terrestrial and offshore sources of sediment.
• Abrasion is caused when rocks or pebbles carried by waves hit the shoreline
• Hydraulic Action is the force exerted by water as it hits the coastline
• These flows of energy and variations in sediment budgets interact with the prevailing geological and lithological characteristics of the coast to operate as coastal systems and produce distinctive coastal landscapes, including those in rocky, sandy and estuarine coastlines.
• The main types of coastal erosion are hydraulic action, abrasion, corrosion, attrition, solution, hydroplaning, saltation, mass movement, and weathering.
• Deposition occurs when wave energy decreases along the coastline, causing sediments to be deposited
• These landscapes are increasingly threatened from physical processes and human activities, and there is a need for holistic and sustainable management of these areas in all the world’s coasts.
• Coasts are the interface between land and the sea, making coastlines highly dynamic landscapes as they are impacted by a wide range of terrestrial and marine processes.
• Longshore drift refers to the movement of sand parallel to the coastline
• Coastlines are a dynamic landscape and system as it is constantly moving and changing.
• Saltation involves small particles being lifted into suspension and then dropped onto the seabed
• Changes along the coastlines are driven by changes to the inputs into the coastal environment which impact on the processes that occur and the outputs produced.
• Attrition occurs when particles are broken down into smaller sizes
• When the inputs and outputs are balanced and equal there is dynamic equilibrium.
• Inputs are factors that are added to the coastal system such as land (rock type and structure, tectonic activity), atmospheric (weather/climate, climate change, solar energy), marine (waves, tides, storm surges) and people (human activity and coastal management).
• Plant life contributes to coastal landscapes by depositing and decaying material on top of which new plants grow, gradually raising the height of the saltmarsh.
• Waves are caused by the friction between wind and water, where energy is transferred from the wind to the water.
• The strength of a wave is dependent on the fetch (distance the wave travels over open water without hitting land), wind speed (higher means more energy) and wind duration.
• There are two main types of waves with different characteristics that result in different beach profiles.
• Destructive waves are more common in high energy environments and are characterized by being large, steep, short wavelength, high frequency waves that plunge vertically and create a powerful backwash.
• Constructive waves are usually small, flat, long wavelength, low frequency waves that steepen relatively slowly until they gently spill over and lose volume and energy due to water percolating through the beach material.
• Erosional processes occur at high energy environments and include hydraulic action, abrasion, attrition, and solution (corrosion).
• Marsden Bay is an example of an erosional coastline and is a concordant coastline, as the rock runs parallel to the coastline.
• The rock at Marsden Bay is made of the resistant rock, Magnesian limestone, which is heavily jointed.
• The landforms at Marsden Bay have formed due to the presence of geological structures, with the location of the bay controlled by where the beds have been folded and are dipping towards the sea.
• This means that the bedding planes are exposed to the sea allowing hydraulic action to weaken the cliff and creating a slippage plane for rockfalls to occur, leading to cliff retreat.
• Depositional landforms on beaches can form from longshore drift, tidal deposition, wave refraction, and storm surges.
• A change in the prevailing wind can cause a spit to retreat and longshore drift to extend the features eastwards.
• A series of recurved spits may form each time there is a series of storms from the south-east, giving a lengthy period of alternated wind direction.
• A spit is unlikely to grow any further because of the faster current of the river carrying material out to sea and the depth of water becoming too great for the spit to build upwards above sea-level.
• The stability of the spit may be increased by the anchoring quality of marram grass.
• At the same time, gentle, low-energy waves entering the sheltered area behind the spit deposit fine silt and mud, creating an area of saltmarsh.
• If a spit develops in a bay into which no major river flows, it may be able to build across that bay, linking two headlands to form a bar.
• Bars straighten coastlines and trap water in lagoons on the landward side.
• A tombolo is a beach that extends outwards to join with an offshore island.
• Cuspate forelands are low-lying triangular-shaped features that extend from the shoreline formed from deposited sediment.
• Sub-aerial processes include weathering and mass movement.
• Weathering can occur mechanically, chemically, or biologically.