2a - Coastal landforms develop due to a variety of interconnected climatic and geomorphic processes Flashcards
The influence of flows of energy on geomorphic processes
- GPE - backwash, tides, causing of rock fall and mass movements
- Solar – drives the wind which drives the waves, the sun which dries up sand through evaporation so that the wind can transfer it through Aeolian processes
- Kinetic – wind and waves and movement of waves which drives longshore drift
The influence of flows of materials on geomorphic processes
- longshore drift moving sediment along beach (W→E in SW UK + N→S in NE UK), closed systems/open systems
- Aeolian flows – wind forming coastal landscapes e.g. sand Dunes
- Currents – can input sediment from off shore
- Rivers – 70 to 80% of sediment, depositional features (Estuaries)
- Mass movement events causing rockfall and slumping
Geomorphic processes -
weathering
- involves the disintegration and decomposition of rocks by the combined action of the weather, plants and anything - Weathering processes – can be regarded as physical, chemical or biological:
Freeze thaw – water enters cracks/joints and expands 10% when it freezes. In confined spaces and exerts pressure causing rocks to split or pieces to break off
Solution - Some salts are soluble in the water so material dissolves
Tree roots – grow into cracks/joints and exerts outward pressure. When trees topple, the roots can exert leverage on rock and soil, bringing them to the surface and exposing them to further weathering
Geomorphic Processes - mass movement
occurs when the forces acting on slope material, Mainly the resultant Force of gravity, exceeds forces holding the material; friction
- Flows and slides – flows are fast and wet where are slides are when soil and rock giveaway and move down a slope
- Landslides and landslips – landslip is the sliding of a mass of land down the slope whereas landslide involves the break up and downhill flow of rock mud and anything in its path
- Soil creep and solifluction - Solifluction is in cold climates were mass of saturated rock waste moves down the slope and soil creep is the slow down hill movement
- Rockfall and slumping - Rockfalls are steep where is slumping is an angled slide (Slumping eg Barton on sea)
Significance of mass movement:
- Rockfall - causes overhanging rock to be unsupported equals fall eg Old Harry rocks
- Landslides – buildup of sediment and rock equals terraced appearance solifluction lobes eg lyme Regis
- Soil creep – Build up of soil on upslope side of walls
Geomorphic Processes - wave erosion
- as waves enter shallower water they bend
- Waves travel faster in deeper water and slower in shallow water due to increased friction and resistance
- Refraction causes the wave to bend towards the coast
- Direction of kinetic energy is 90° to the Wavecrest
- Waves band around a headland focusing most of the kinetic energy and erosion therefore there’s more deposition in the bays as waves have lost their kinetic energy and have Cliff sediment. This is a negative feedback because the bay has more deposition and the headland has more erosion
Drift aligned beach – longshore drift – buildup of sediment on one side. Smaller sediment on larger side due to attrition
Swash aligned beach – no longshore drift – smaller sediments at the front and biggest sediment at the bottom because swash is more powerful than backwash
Geomorphic Processes - transportation and deposition
Transportation:
- suspension – small particles of sand, silt and clay can be carried by currents (large particles during storms) =browny water
- Traction – the largest particles get pushed along the sea by the floor by flow → rolling
- Solution – minerals that have been dissolved into the mass of moving water
- Saltation – turbulent flow, many pick up sand sized particles and carry short distances; particles also Can get dislodged
Deposition:
- when the rate of sediment accumulation exceeds the rate of removal
- When waves slow down immediately after breaking
- At the top of the swash, where for a quick moment the water is no longer moving
- During the backwash, when water percolates into beach material
- And low energy environments, such as those sheltered from the wind and waves Eg estuaries
Geomorphic Processes - Erosion (+diif processes) and Flocculation
Erosion – the removal of weathered material by the action of gravity, water, wind or ice. The fragments of debris may then be used to wear down other material
Eosional processes:
- Hydrochloric acid – waves break on cliff face
- Abrasion - waves armed with rock particles scour coastline
- Wave pounding – when a mass of breaking wave exerts pressure so rock weakens
- Attrition – rocks carried by wave collide and got rounded/erode
Flocculation – melting of freshwater and saltwater causing flocculation of clay particles were fine, light materials clump due to electrical charges between them in saline conditions equals heavier and sinks to seabed
The formation of distinctive landforms - influenced by erosion
Bays and Headlands
- form adjacent as they are usually on a discordant coastline where there’s presence of bands of rock of differing resistance to erosion
- weak rock is eroded quickly through processes of abrasion and hydraulic action forming bays and more resistant hard rock forms headlands. Usually kilometres wide. Wave refraction - negative feedback loop
- Isle of Purbeck has east facing discordant coastline and south facing concordant.
- once bay has formed in the softer rock between 2 headlands, wave refraction will occur, each wave slowed by friction as it reaches shallower water nearing the coastline/headland
- due to wave refraction = less energy focused on bay = deposition - constructive waves = neg feedback slows growth
- at the same time, the part of wave crest in deeper water, approaching bay moves faster as its not slowed by friction = wave bends or refracts around headland = wave energy focused on headland and so is erosion, energy is dissipated in the bays = deposition
- LSD moves eroded material from headland to build up bays
The formation of distinctive landforms - influenced by erosion
Cliffs and Shore Platforms
Cliff Formation -
- soft rock equals sloping cliffs, hard rock equals resistant steep cliffs. igneous and metamorphic rocks are harder = more resistant to erosion
- destructive waves break repeatedly on steep coastlines. Undercutting occurs from focused erosion due to low tidal range where the wave cut notch than forms.
- This causes weakened support which then collapses and the steep profile/cliff is formed.
- the regular removal of debris at the foot of cliff by wave action ensures that the cliff profile remains steep and that cliffs retreat inland, parallel to the coast
- as sequence of undercutting, collapse and retreat continues, the cliff becomes higher
Shore platform
- At its base a gently sloping shore platform is cut into the solid rock and a wave/shore platform is formed (4-500m wide).
- a shore platform is a horizontal or gently sloping surface at around 0-3 degrees, backed by a cliff
- although appearing to be flat, they are dissected by abrasion due to large rock debris being dragged along the surface by destructive waves, and so large rock will accumulate, too large to be moved by waves.
- friction from the platform slows down waves so that they break on the platform rather than at the cliff base = less undercutting
- At low Tide marine organisms can speed up weathering
The formation of distinctive landforms - influenced by erosion
Geos and Blowholes
Geos
- coastal Gorge created when a fault line is eroded. Joints and faults got enlarged by Marine erosion as these weak points are eroded more rapidly by wave action than the more resistant rock around them. Hydraulic action sig in forcing air and water into the joints and weakening rock Strava. Eg Huntsman’s Leap 35m deep and eroded along a large joint in the carboniferous limestone
- Occurs at mega fault running 90° to a coastline so it can be exploited. Due to a small tidal range. That is focused erosion on the hard rock from destructive waves especially in high energy storms. Solar, GDP to power waves – kinetic energy. form tunnel like caves which when eroded, roof collapses and forms geo
Blowhole
- Vertical cleft in coastal cliffs linking sea cave to Clifftop. Waves trap air in a cave – hydrochloric action and forces puncture the roof of cave and water/spray is driven through the roof eg Devils Cauldron 45m deep
- = erosion and when it collapses it forms a Geo. Hard rock by faulting due to destructive high kinetic energy waves focused erosion small tidal range and the surface of the blow hole is weathered - biological, chemical, free thaw and then collapses.
The formation of distinctive landforms - influenced by erosion
Caves, Arches, Stacks and Stumps
Cracks are resistant rocks with weaknesses
- Cracks at the base of a Headland where waves erode by solution and hydraulic action which pressure rises air, forcing cracks to widen which forms wave cut notches through processes of abrasion and hydrochloric action deepens the notch forming a cave
- Wave refraction – destructive waves concentrate kinetic energy and erosion on the sides of the cave. When 2 caves are aligned the waves can cut through forming an arch. Wave cut notches widen the base of the arch
- Overtime the arch becomes unstable and collapses under its own weight to form a pillar of rock separated from the heartland
- Further erosion at the base of the stock may cause it to collapse and form a small, flat portion of the original stock – a stump. The broken material will then be eroded and transported/deposited within the bay
The formation of distinctive landforms - influenced by deposition
Beaches
- swash aligned – waves move and break parallel with the coast and sediment is moved up and down
- Drift aligned – due to angled prevailing winds, waves break at an angle pushing sediment to one side of the beach – LSD
- Often in dynamic equilibrium – one year cycle – winter has destructive waves and Summer has constructive
- Sources of sediment is fluvial, cliffs and offshore
- Sand Beach is have a gentle gradient, small sediment and are often sheltered and have constructive waves
- Single beach all pebbly, cobbles and rock and berms and ridges are common
The formation of distinctive landforms - influenced by deposition
spits
- spits form due to longshore drift where deposited material builds up due to prevailing winds blowing at an angle to the coast line. Energy is dispersed, lost as the wave refracts and current spreads leading to deposition. Extended stretch of deposited beach material that projects into the sea and joins to the mainland at one end
The formation of distinctive landforms - influenced by deposition
Onshore Bars
longshore drift causes a spit to grow across an indentation in the coastline, enclosing a bay or Cove. As sea level rises, constructive waves transfer sediment from the sea bed onto the bar
The formation of distinctive landforms - influenced by deposition
Tombolo
- longshore drift causes a spitbto grow until it joins an island
- Wave refracts, bending around an island and depositing sediment
