Types of weathering affecting coastal landscapes

Weathering is the natural process of breaking down rocks and materials without moving them, playing a crucial role in shaping coastal environments. There are three primary types of weathering that impact coasts, each with distinct mechanisms.

Mechanical weathering in coastal areas

Mechanical weathering involves the physical breakdown of rocks without altering their chemical makeup. It is particularly significant in coastal regions like the UK due to the constant exposure to seawater and temperature changes.

Salt weathering:

• Occurs in all coastal areas.
• Seawater seeps into small cracks within rocks.
• As the water evaporates, salt crystals form inside these cracks.
• The expanding crystals exert pressure on the surrounding rock.
• Over time, repeated cycles of evaporation and crystal growth widen the cracks, eventually causing the rock to fragment.

Freeze-thaw weathering:

• Occurs in colder coastal areas.
• Water enters cracks in rocks and freezes during low temperatures.
• The freezing water expands, putting stress on the rock.
• Repeated freezing and thawing cycles cause the cracks to enlarge, leading to rock disintegration.

Chemical weathering in coastal environments

Chemical weathering involves the alteration of a rock's chemical structure, often dissolving or weakening it over time. This process is prevalent in warmer, wetter coastal conditions.

Carbonation weathering:

• Rainwater absorbs carbon dioxide from the atmosphere, forming a mild carbonic acid.
• This acid reacts with rocks containing calcium carbonate, such as chalk or limestone.
• The reaction dissolves parts of the rock, gradually wearing it away.

Biological weathering along coasts

Biological weathering occurs when living organisms contribute to the breakdown of rocks, often through physical or chemical means, particularly in coastal cliff areas.

There are two main methods of biological weathering:

1. Animal activity - Animals burrow into soil on cliff tops, destabilising the ground and breaking apart underlying rock structures.
2. Plant root action - Roots grow into cracks in rocks, exerting pressure as they expand and forcing the cracks to widen over time.

Processes of mass movement and their impact on coasts

Mass movement refers to the downslope movement of material under the influence of gravity, often accelerating coastal retreat and reshaping landscapes.

Mechanisms and causes of mass movement

• Gravity's role - Mass movement happens when the force of gravity overcomes the forces holding material in place on a slope.
• Impact on coasts - Leads to rapid retreat of coastal cliffs as material falls or slides away.
• Contributing factors:
  • Water saturation - Wet material is heavier and acts as a lubricant, making movement more likely.
  • Slope undercutting - Erosion at the base of a slope destabilises the material above, increasing the risk of collapse.

Types of mass movement in coastal areas

• Slides - Material moves downslope in a relatively straight line, often along a defined plane of weakness.
• Slumps - Material shifts with a rotational motion, creating a curved scar on the landscape as it moves.

The four main processes of coastal erosion

Erosion is the wearing away and removal of material from the coastline, driven by the power of waves and water. There are four key processes that contribute to coastal erosion.

Hydraulic action and its erosive power

• Wave impact - Waves crash against coastal rocks, compressing air trapped in cracks.
• Pressure build-up - This compression creates significant pressure within the rock.
• Crack expansion - Repeated wave action widens existing cracks, eventually dislodging fragments of rock.

Abrasion as a grinding force

• Particle impact - Sediments and particles carried by waves scrape and grind against coastal rocks.
• Surface wear - This rubbing action removes small pieces of rock, smoothing and wearing down surfaces over time.

Attrition and particle breakdown

• Collision effect - Eroded particles in the water collide with each other during wave action.
• Fragmentation - These collisions break the particles into smaller pieces.
• Rounding edges - The friction from repeated impacts smooths the edges of particles, creating rounded shapes.

Solution through chemical erosion

• Acidic water - Seawater absorbs carbon dioxide, forming a slightly acidic solution.
• Rock dissolution - This acidic water reacts with certain rocks, like chalk and limestone, dissolving them over time and contributing to coastal retreat.

Characteristics and effects of destructive waves

Destructive waves are a powerful force in coastal erosion, actively removing material from shorelines due to their specific characteristics.

Features of destructive waves

• High frequency - Typically break at a rate of 10-14 waves per minute, delivering constant energy to the coast.
• Steep profile - These waves are tall and steep, maximising their impact on the shoreline.
• Powerful backwash - The backwash, or movement of water down the beach, is stronger than the swash, or upward movement, leading to a net loss of material.

Erosional impact of destructive waves

• Material removal - Due to the stronger backwash, destructive waves strip sediment and debris from the coast, contributing to erosion.
• Landscape change - Their persistent action shapes cliffs and other coastal features by continuously wearing them down.