The definition and importance of geomorphic processes

Geomorphic processes are natural mechanisms that shape and alter the Earth's landscapes over time. These processes are fundamental in creating and modifying landforms, influencing everything from coastal cliffs to river valleys.

Core components of geomorphic processes

• Weathering - The breakdown or disintegration of rocks in their original location, often near the Earth's surface.
• Mass movement - The downhill movement of surface material due to gravity, commonly seen at coastal cliffs.
• Erosion - The wearing away of rock and soil by natural agents like water, wind, or ice.
• Transportation - The movement of eroded materials from one location to another by forces such as rivers or waves.
• Deposition - The laying down of transported materials, which can form new landforms like beaches or deltas.

Types and mechanisms of weathering

Weathering is a critical geomorphic process that involves the decomposition or disintegration of rocks without moving them from their original place. It prepares materials for further erosion or mass movement and is categorised into three main types: chemical, mechanical (physical), and biological.

Categories of weathering processes

Freeze-thaw weathering process

• Initial infiltration - Water seeps into cracks within rocks during warmer periods.
• Ice expansion - As temperatures drop, the water freezes into ice, expanding by about 9% and exerting significant pressure on the surrounding rock, which widens the cracks.
• Fragment detachment - Repeated cycles of freezing and thawing progressively weaken the rock, eventually causing fragments to break off. These fragments often accumulate as scree at the base of the rock face.

Processes and forms of mass movement at the coast

Mass movement refers to the downhill shift of surface materials under the influence of gravity, often prominent at coastal areas where cliffs are destabilised by wave action. This process significantly shapes coastal landscapes through various forms of movement.

Common forms of mass movement at coastal regions

• Rockfall - Individual fragments or chunks of rock detach and fall from a cliff face, often triggered by freeze-thaw weathering.
• Landslide - Large blocks of rock slide rapidly downslope along a linear shear-plane, typically lubricated by water.
• Mudflow - Saturated clay or similar material flows downhill, combining elements of sliding and slumping.
• Rotational slip/slump - Loose material, often sand or clay, slumps along a curved shear-plane, usually after heavy rainfall saturates the sediment.
• Sliding - Rock or loose material moves downhill along a slip plane, such as a bedding plane, often initiated by earthquakes or heavy rain.
• Slumping - Weak rocks like sands and clays collapse, frequently at the coast, due to saturation from rainfall making the material heavy and unstable.

Slumping process at coastal cliffs

1. Water saturation and instability - Rain soaks into porous upper layers of rock (e.g., sandstone), but cannot drain through an underlying impermeable layer (e.g., clay). This saturates the upper material, making it significantly heavier and increasing pressure within the cliff.
2. Shear plane development and initial collapse - The increased weight causes a curved shear plane to develop within the saturated material. A section of the cliff then tears away and slides downwards along this curved plane, with gravity pulling the slab of rock to the beach, where loose debris forms a 'toe' at the base.
3. Ongoing weakening by weathering - Processes like freeze-thaw action continue to weaken the exposed cliff face and the slumped material over time, making it more prone to further movement.
4. Wave erosion and subsequent events - Wave action at the base of the cliff removes the accumulated 'toe' and undercuts the cliff face, removing support. This further destabilises the cliff, allowing subsequent rainfall events and gravitational forces to trigger new slumping episodes along developing slip planes.

Interactions between weathering and mass movement in shaping landscapes

Weathering and mass movement are interconnected geomorphic processes that work together to sculpt the Earth's surface, particularly in dynamic environments like coastal zones. Their interactions create and modify landforms over time.

Key interactions between weathering and mass movement

• Weathering as a precursor - Processes like freeze-thaw and salt weathering weaken rocks, making them more susceptible to mass movement events such as rockfalls or landslides.
• Mass movement exposing new surfaces - When material moves downhill, it exposes fresh rock surfaces to weathering agents like water and air, accelerating further breakdown.
• Role of water - Water plays a dual role by contributing to chemical weathering through reactions like hydrolysis and by lubricating slip planes in mass movement events like slumping or sliding.
• Coastal dynamics - At the coast, wave undercutting exacerbates mass movement by destabilising cliffs, while weathering continuously weakens the rock, creating a cycle of collapse and erosion.
• Cumulative impact - The combined effect of these processes results in significant landscape changes, such as the retreat of coastal cliffs or the formation of scree slopes at the base of eroded rock faces.