Marine processes shaping coastal zones

Coastal zones are dynamic environments shaped by a variety of marine processes. These processes involve the interaction of waves, wind, and other natural forces that continuously alter the coastline through erosion, transportation, and deposition.

Key marine processes in coastal environments

• Wave action - Waves are the primary force in coastal shaping, with two distinct types:
  • Constructive waves - These have a long wavelength, low height (under 1 metre), low frequency (around 6-8 per minute), and a stronger swash than backwash, promoting deposition.
  • Destructive waves - These feature a short wavelength, high height (over 1 metre), high frequency (around 10-12 per minute), and a stronger backwash than swash, leading to erosion.
• Wind action - Winds drive wave formation and can influence sediment movement, particularly in exposed coastal areas.
• Mass movements and weathering - These contribute to the breakdown and movement of coastal materials, often weakening cliffs and aiding erosion.
• River and ice actions - Rivers deliver sediment to coasts, while ice can shape high-latitude coastlines through abrasion and deposition.

Transportation processes in coastal waters

• Traction - Larger particles, such as pebbles, are dragged along the sea floor by wave action.
• Saltation - Smaller particles, like sand grains, bounce along the sea floor due to wave energy.
• Suspension - Very fine materials, such as silt, are held within the water column and carried by currents.
• Solution - Dissolved sediments, including minerals like calcium, are transported within the water itself.

Wave refraction and its effects

Wave refraction happens when waves approach an uneven coastline or at an angle, altering their speed and direction. This process reduces wave velocity and can cause wave fronts to align parallel to the shore.

Energy is concentrated on the sides of headlands, increasing erosion, while it is dispersed in bays, encouraging deposition. Incomplete refraction often results in longshore drift, where sediment is moved along the coast by angled wave action.

Erosional processes and resulting landforms

Erosion is a key process in shaping coastal landscapes, wearing away rock and sediment through various mechanisms. This results in distinctive landforms that reflect the intensity and type of erosion at work.

Mechanisms of coastal erosion

• Abrasion (corrasion) - The grinding action of sediment carried by waves wears down cliffs and other coastal features.
• Hydraulic action - The force of water and trapped air in waves exerts pressure on rock surfaces, breaking them apart.
• Solution (corrosion) - Chemical reactions dissolve minerals in rocks, particularly calcium, leading to their breakdown.
• Attrition - Sediment particles carried by the sea collide and wear each other down, reducing their size over time.

Erosional landforms along coastlines

• Headlands and bays - Formed where rocks of varying resistance are present; harder rocks create protruding headlands, while softer rocks erode into recessed bays.
• Cliffs - Steep rock faces created by wave erosion at their base, often steepened by weathering and mass movement from above.
• Wave-cut platforms - These are flat or gently sloping (around 1°) surfaces, typically less than 500 metres wide, formed as cliffs retreat due to erosion, leaving a platform at the base with less steep cliffs behind.
• Caves, arches, and stacks - On coastlines with a single rock type, weaknesses like faults can erode into caves; continued erosion may form arches, which eventually collapse to leave isolated stacks.

Depositional processes and associated landforms

Deposition occurs when wave energy decreases, sediment supply is high, or coastlines have irregular shapes that trap material. This process builds up coastal features over time.

Causes of coastal deposition

• Reduced wave energy - Lower velocity waves cannot carry sediment, leading to its deposition.
• Abundant material supply - Large amounts of sediment from rivers or eroded cliffs contribute to landform creation.
• Indented coastlines - Irregular shapes, such as inlets, slow down waves and encourage sediment to settle.

Depositional landforms along coastlines

• Beaches - Accumulations of sand or shingle formed by constructive waves, ample sediment supply, or strong onshore winds pushing material landward during low tides.
• Spits - Narrow ridges of sand or shingle attached to land at one end, often found at river mouths or along indented coasts, formed by longshore drift.

Formation and types of coral reefs

Coral reefs are unique marine ecosystems built by small organisms called corals, which extract calcium salts from seawater and combine them with carbon dioxide to form calcium carbonate skeletons. Their formation and distribution are influenced by specific environmental conditions.

Conditions required for coral growth

• Water temperature - Must be above 20°C to support coral metabolism and growth.
• Water clarity and salinity - Clear, salty water is essential for photosynthesis by symbiotic algae within corals.
• Water depth - Shallow coastal waters allow sunlight to penetrate for algae growth.
• Nutrient supply - A good supply of plankton and water circulation provides food and oxygen for corals.

Types of coral reef formations

• Fringing reefs - These grow directly outward from the shore of an island or coastline, forming a border along the edge.
• Barrier reefs - Separated from the coast by a deep channel, these reefs form parallel to the shoreline but at a distance.
• Atolls - Circular reefs that enclose a shallow lagoon, often formed around submerged volcanic islands due to land subsidence or rising sea levels.

Characteristics and distribution of mangroves

Mangroves are specialised, salt-tolerant forests found in tropical coastal zones and tidal estuaries. They play a vital role in coastal ecosystems by stabilising sediment and supporting biodiversity.

Features of mangrove ecosystems

• Salt tolerance - Adapted to thrive in saline conditions through specialised root systems that filter salt or excrete it.
• Nutrient-rich waters - Decaying organic matter in mangrove areas enriches the surrounding water, supporting a diverse food web.
• Root structures - Unique roots, such as pneumatophores, allow mangroves to access oxygen in waterlogged, anaerobic soils.