In this section, we delve into the fascinating world of coastal geomorphology, exploring the processes of erosion and deposition that shape coastal landscapes. We will examine the characteristics and formation of various coastal landforms such as wave cut platforms, cliffs, stacks, spits, and beaches.
Introduction to Coastal Erosion and Deposition
Coastal erosion and deposition are natural processes that play a vital role in shaping the coastline. Erosion involves the wearing away of the coast by the sea, wind, and other natural forces. Deposition, on the other hand, refers to the accumulation and laying down of sediment carried by water, wind, or ice.
Wave Cut Platforms
- Definition: Wave cut platforms are flat areas that extend from the base of coastal cliffs into the sea, created by the erosive action of waves.
- Formation Process:
- The process starts with wave impact at the base of a cliff, eroding the rock primarily through hydraulic action and abrasion.
- Over time, a notch forms at the high tide line. Continuous erosion at this notch causes overhanging rock to collapse.
- The repeated collapsing of the cliff face leads to its retreat, leaving behind a flat, often rocky platform.
- Characteristics:
- These platforms are most noticeable at low tide, revealing a flat surface.
- They may exhibit features like wave-eroded grooves, rock pools, and occasionally, marine organisms.
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Cliffs
- Definition: Cliffs are steep or vertical rock faces at the edge of the coast, formed mainly due to erosive processes.
- Formation Process:
- Coastal cliffs are formed by the erosion of rock layers. Wave action attacks weaker parts of the rock, while subaerial processes like weathering and mass movement contribute to their formation and evolution.
- The type of rock plays a crucial role in the development of cliffs. Harder rocks form more pronounced and steeper cliffs, whereas softer rocks are more prone to erosion.
- Characteristics:
- The appearance of cliffs can vary greatly, with some being hundreds of meters high and others much lower.
- Often, they display strata of different rock types and may have vegetation growing on their tops or sides.
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Stacks
- Definition: Stacks are vertical columns of rock, standing isolated from the main coastline, often remnants of headlands.
- Formation Process:
- The formation begins with wave action eroding the sides of a headland, creating cracks. These cracks gradually evolve into caves.
- When caves on opposite sides of a headland meet, they form a natural arch. Continued erosion and weathering eventually cause the arch to collapse, leaving a stack.
- Characteristics:
- They are typically composed of more resistant rock types.
- The size and shape of stacks change over time due to ongoing erosion, and they may eventually collapse to form stumps.
Image courtesy of Derek Mayes
Spits
- Definition: Spits are elongated stretches of sand or shingle that project from the land into the sea.
- Formation Process:
- Spits are formed by the process of longshore drift, where sediment is transported along the coastline by waves. When the coastline changes direction or where the current slows, sediment accumulates and forms a spit.
- Characteristics:
- They can be straight or curved, and their shape can be influenced by changes in wind direction and wave approach.
- Spits often have features like salt marshes or mudflats on the landward side and are dynamic structures that can change shape over time.
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Beaches
- Definition: Beaches are accumulations of sediment, such as sand, pebbles, or shingle, along coastlines.
- Formation Process:
- Beaches are formed by the deposition of material from waves, rivers, or wind. The size and composition of the sediment depend on the local rock types and the energy of the waves.
- Characteristics:
- The shape and size of beaches can vary, with some being wide and sandy, while others are narrow and covered with pebbles.
- Beach profiles can change seasonally: wider, flatter beaches form in summer with gentler waves, while steeper, narrower beaches form in winter due to higher energy waves.
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Factors Influencing Coastal Erosion and Deposition
- Wave Energy: The energy of waves is a crucial factor. High-energy waves contribute to significant erosional features, whereas low-energy waves are associated with sediment deposition.
- Tide Range: The range between high and low tide can affect the extent of erosion and the formation of coastal features.
- Rock Type and Structure: The geological composition and structure of the coastline dictate the rate and style of erosion. Harder rocks form more resilient features, while softer rocks are more easily eroded.
- Human Activities: Coastal management practices, such as the construction of sea walls and groynes, can significantly alter natural erosional and depositional processes.
Understanding these landforms is essential for comprehending the dynamic nature of coastlines and the balance between land and sea. These formations are not only of geological interest but are also crucial for coastal management and protection strategies.
FAQ
Subaerial processes, including weathering, mass movement, and runoff, significantly impact coastal landscapes. These processes operate above water and influence the land's stability and structure. Weathering, which includes physical, chemical, and biological weathering, breaks down rock on the coast, making it more susceptible to erosion by waves. Mass movement, such as landslides or rockfalls, often occurs on weakened cliff faces, contributing to the retreat of cliffs and the formation of debris at the base. Runoff from rainwater can further erode and transport materials, shaping coastal features. Overall, subaerial processes work in conjunction with marine processes to sculpt coastal landscapes.
Human activities significantly impact coastal landforms, often accelerating or impeding natural processes. Coastal development, including the construction of buildings, roads, and seawalls, can interfere with natural erosion and deposition patterns, leading to increased erosion in some areas and sediment buildup in others. Coastal defences, such as groynes and breakwaters, are designed to protect areas from erosion but can disrupt sediment transport, affecting beaches and spits downstream. Pollution and habitat destruction can also affect the stability and health of coastal ecosystems, which in turn can influence coastal processes. Climate change, driven by human activity, is causing sea-level rise and increased storm frequency, which intensifies coastal erosion and reshapes coastal landforms.
Tides, the regular rise and fall of sea levels, play a significant role in shaping coastal landforms. The tidal range, or the difference between high and low tide, can determine the extent of wave action on the coast. In areas with a high tidal range, waves can reach further inland, influencing the erosion and deposition processes. This can lead to the formation of extensive mudflats and salt marshes in estuaries and bays. Tides also influence the development of features like rias and fjords, where rising sea levels flood river valleys. The intertidal zone, the area between high and low tide, is a dynamic environment where many coastal processes occur, influencing the formation of beaches and other coastal landforms.
Vegetation plays a crucial role in the development and stability of coastal landforms. Plants, especially in dune systems, help to stabilize sediments and reduce the impact of erosion. The roots of vegetation bind the soil together, making it less susceptible to being washed away by waves or blown away by wind. In sand dune systems, plants trap and stabilize the sand, aiding in dune formation and growth. Vegetation also acts as a natural barrier against coastal erosion, absorbing wave energy and reducing the impact on the coastline. In salt marshes and mangroves, vegetation slows down water flow, encouraging sediment deposition and landform development.
Lithology, or the physical characteristics of rocks, plays a crucial role in the formation of coastal landforms. Different rock types have varying resistance to erosion. For example, harder rocks like granite and basalt are more resistant and tend to form prominent features like cliffs and headlands. Softer rocks, such as chalk or clay, are easily eroded, leading to the formation of bays and inlets. The structure of the rock, including its composition, layering, and fault lines, also influences how it erodes and what landforms are created. For instance, rocks with many fissures or joints are more susceptible to erosion processes like hydraulic action, which can lead to the formation of features such as caves and arches.
Practice Questions
Wave cut platforms are formed through the erosive action of waves at the base of coastal cliffs. This process begins with waves attacking the cliff base, leading to the formation of a notch through hydraulic action and abrasion. As the notch enlarges, the cliff becomes unstable and collapses. This cycle of erosion and collapse causes the cliff to retreat, leaving behind a flat, rocky platform. Wave cut platforms are significant as they reveal the history of coastal erosion, showcasing past sea levels and erosion rates. They also serve as natural barriers, reducing the impact of waves on the coast and providing unique habitats for marine life.
Spits are elongated stretches of sand or shingle extending from the land into the sea, formed primarily by the process of longshore drift. This process involves the transportation of sediment along the coast by waves, accumulating where the coastline changes direction or current slows. Spits can be straight or curved, often featuring a recurved end due to changes in wind and wave direction. Their landward sides may have salt marshes or mudflats. Spits play a crucial role in coastal systems by acting as natural barriers against sea currents and waves, protecting inland areas and sometimes contributing to the formation of new habitats. Their dynamic nature makes them significant for studying coastal processes and managing coastal erosion.
