Geography – Coastal environments | e-Consult

Marine erosion and sub-aerial processes are two key mechanisms that contribute to the evolution of coastal landscapes. Marine erosion refers to the erosive action of waves, tides, and currents, while sub-aerial processes encompass weathering, mass movement, and fluvial erosion acting on coastal slopes.

Marine erosion is primarily driven by wave action. Hydraulic action, the force of water entering cracks and crevices, compresses air and causes the rock to fracture. Abrasion, the grinding action of sediment carried by waves, wears away the coastline. Attrition, the collision of sediment particles, breaks them down into smaller pieces. Corrasion, the impact of large waves carrying boulders, further erodes the coastline. The effectiveness of marine erosion depends on wave energy, which is influenced by factors such as fetch, angle of wave approach, and coastal orientation. High-energy wave climates, like those found on exposed coastlines, experience more intense marine erosion.

Sub-aerial processes, on the other hand, are primarily concerned with weathering and mass movement on coastal slopes. Weathering weakens the rock, making it more susceptible to erosion. Physical weathering, such as freeze-thaw action, can break down rocks. Chemical weathering, such as oxidation and hydrolysis, can dissolve or alter the rock. Mass movement, including landslides, slumps, and creep, transports weathered material downslope. The susceptibility to mass movement depends on factors such as slope angle, rock type, and rainfall. Areas with steep cliffs and unstable slopes are more prone to mass movement.

The relative importance of marine erosion and sub-aerial processes varies depending on the coastal environment. In areas with high wave energy and resistant rocks, marine erosion is typically the dominant process, leading to the formation of cliffs and wave-cut platforms. In areas with softer rocks and lower wave energy, sub-aerial processes may be more important, leading to the formation of gentler slopes and more extensive areas of weathering and mass movement. For example, the chalk cliffs of Dover are primarily shaped by marine erosion, while the clay cliffs of the Sussex coast are more susceptible to sub-aerial processes.

It's important to note that marine erosion and sub-aerial processes often work together. Sub-aerial weathering weakens the rock, making it more vulnerable to marine erosion. Mass movement can also transport material into the sea, contributing to coastal erosion. Therefore, a comprehensive understanding of coastal landscapes requires considering both sets of processes.