Factors influencing coastal environments

Coastal environments mark the dynamic boundary between land and sea, known as the coastline. This transition zone includes onshore areas extending up to 60 km inland and offshore zones reaching as far as 370 km out to sea. The diversity of coastal landscapes worldwide results from multiple interacting factors.

Key influences on coastal diversity

• Land factors - Physical processes, geological structures, relief variations, river sediment input, and local ecosystems all shape the coastal landforms.
• Sea factors - Marine processes, changes in sea level, water depth variations, and marine ecosystems influence how the sea interacts with the coast.
• Weather and climate factors - Wind strength and direction, rainfall patterns, temperature fluctuations, storm events, storm surges, and long-term climate change impact coastal dynamics.
• Human activity factors - Settlements, coastal development, and management strategies by humans alter natural coastal processes and landforms.

These elements combine to create unique coastal environments, where land, sea, and atmosphere interact, alongside human influences.

Marine processes and the role of waves

Marine processes are primarily driven by waves, which play a central role in shaping coastal landscapes through erosion, transportation, and deposition of materials. Waves are generated by winds blowing across the sea surface, with friction between wind and water initiating their motion.

How waves form and behave

• Wave generation - Winds create waves as they blow over the sea, with wave strength determined by wind intensity, duration, and the distance over which the wind blows (known as fetch).
• Wave behaviour near the coast - As waves approach shallower water near the shore, friction with the sea bed causes them to tip forward and break, producing a forward surge of water called swash that moves up the beach.
• Return flow - After the swash loses energy, water flows back down the beach under gravity, termed backwash, influencing whether material is deposited or eroded.

Types of waves and their impact on the coast

Waves are categorised into constructive and destructive types based on the balance between swash and backwash. This balance determines whether a wave builds up or erodes the beach.

Characteristics of constructive and destructive waves

Constructive waves contribute to beach growth by leaving more material behind, while destructive waves remove material, shaping the coastline through erosion.

Processes of erosion, transport, and deposition

Marine processes involve several mechanisms through which waves alter coastal landscapes. These include various forms of erosion, the movement of materials along the coast, and the eventual deposition of sediments.

Mechanisms of coastal erosion

• Hydraulic action - The sheer force of waves striking cliffs compresses air into cracks, widening them over time and breaking apart rock.
• Abrasion - Waves carry stones and debris that are thrown against cliffs, grinding and wearing down the rock surface.
• Corrosion (solution) - Seawater dissolves certain types of rock, particularly those with soluble minerals, leading to gradual cliff retreat.

Transport and deposition processes

• Attrition - Material carried by waves collides with other debris, becoming smaller and more rounded over time, forming pebbles and sand, though it does not directly erode the coast.
• Longshore drift - Waves approaching the shore at an angle move sediment along the beach in a zig-zag pattern. Swash carries material up the beach diagonally, while backwash pulls it straight down, resulting in a net movement of sediment along the coast.
• Deposition - When waves lack the energy to carry material further, they deposit it, forming new coastal features. Lighter and smaller materials are typically carried further before being deposited.

Land processes shaping coastal landscapes

On the landward side of the coastline, terrestrial processes also contribute significantly to shaping coastal environments. These processes break down and move materials, altering the landscape over time.

Key terrestrial processes at the coast

• Weathering - Rocks are broken down through physical and chemical means, such as freeze-thaw action, salt crystal growth, acid rain effects, and plant root expansion within cracks.
• Erosion - Wind and rain wear away exposed rock surfaces, gradually removing material from the land.
• Mass movement - Gravity causes cliff material to move downwards in forms such as rock falls (sudden drops of rock), slumping (slow sliding of saturated soil), and landslides (large-scale movement of rock and debris), reshaping the coastal profile.