Flashcards in KQ1 - What processes and factors are responsible for distinctive coastal landforms? Deck (34)
What are the factors which affect wave strength?
• Depth of water
• Strength and frequency of dominant wind
• Length of the fetch
o Longer fetch = higher energy = larger waves
• Wind and wave strength / direction
o Waves usually have more energy when they hit the beach straight on
• Time wind blows over water
• Sea flow gradient
What are constructive waves?
Low backwash; high swash; low wave frequency: form a wide, sloping beach
What are deconstructive waves?
high backwash; low swash; high wave freq. Form a steep, narrow beach
What types of erosion occur in coastal environments?
• Hydraulic action: breaking waves force air into joints and cracks in the cliff surface, meaning the compressed air has the power to loosen and break away pieces of rock
• Abrasion/corrosion: waves hurl sand particles and pebbles at the cliff face
• Attrition: rocks and pebbles collide with each other as they are moved by waves, and overtime the rough edges are made smoother into smaller sand particles.
• Solution: Acids in the sea water dissolve some types of rock such as chalk or limestone. (e.g. Limestone + H20 = )
What factors affect the rate of marine erosion?
- Wave energy
- Beach width
- Wave orientation
- Sea level change
- Human influence
What is flocculation?
- a chemical process where salt causes the clumping together of very small clay particles into larger masses that are too heavy to remain suspended.
What factors affect the amount of deposition?
• LSD as a result of waves breaking at an angle to the shoreline (direction of wind)
• Dominance of constructive wave action
• Sheltered areas with low wave energy (short fetch)
• Presence of structures or vegetation e.g. groynes
• Input of silts or clays from a river which enters the sea
• Beach gradient/profile
What are the types of transportation in coastal areas?
• Solution: salts dissolved from the rocks by the seawater are carried in solution
• Suspension: small particles can be carried in suspension by the waves
• Saltation: pebbles will be bounced along the seafloor
• Traction: large rocks will be rolled along the seafloor
How does long-shore drift occur?
1. Waves approach the beach at a similar direction to the wind
2. Swash carries material up the beach at the same angle as the waves/wind
3. Backwash returns down the beach at right angles to the water, under the influence of gravity
4. Material is slowly moved along the beach in a zig-zag pattern
What is swash?
water movement up the beach
What is backwash?
water movement down the beach
What are sub-aerial processes?
The combination of weathering and mass movement processes operating on cliff faces
What are the three types of weathering?
Name the physical weathering
- Solution / corrosion
- Wetting / drying
- Freeze thaw
What is solution / corrosion?
- saltwater from the sea leads to growth of salt crystals in rocks. The salt crystals expand and force rocks to disintegrate. Rocks containing limestone are particularly susceptible to corrosion due to the carbonic acid in the sea which dissolves the limestone.
What is wetting / drying?
- softer (e.g. clays and shales) and exposed rocks are prone to expansion and contraction as they become wet and then dry out. Water freezes at temperatures below 0˚C and expands by 9%. This causes weaknesses in the rock, and they often spall curved sheets called onion skin weathering. Marine processes attack and erode easily.
What is freeze thaw?
- thermal expansion and contraction of a rock during rising and falling temperatures creates pressure, causing the rock to disintegrate
What are examples of chemical weathering?
What is carbonation? (limestone)
- rain water mixes with the CO2 in the atmosphere to form weak carbonic acid. This reacts with calcium carbonate in some rocks, such as limestone, to produce calcium bicarbonate which dissolves in water. Carbonation occurs quicker in lower temperatures because colder water holds more dissolved carbon dioxide gas.
What is oxidation? (iron)
minerals containing iron (Fe) in rocks in contact with oxygen react to form iron oxide (rust), which causes rocks to disintegrate. Oxidation is sped up by higher temperatures as the molecules have more energy.
What is a form of biological weathering?
- Animals and plants: plant roots can grow down through cracks in rock surfaces and push them apart, loosening fragments. Decaying plants and animal remains make acids which eat away at rocks below.
What factors affect the rate of weathering?
• Temperature range
• Amount of precipitation
• Rock type: coherence; presence of lines of weakness; chemical composition
• Amount of vegetation
What types of mass movement are there?
- Rock falls
What are rock falls?
• Occur on steep slopes (>70˚)
• Initial cause may be weathering or erosion
• One rocks are detached they fall due to gravity
What are slides?
• Sliding material maintains its shape until it impacts at the bottom of a slope, leading to slumped terraces
• Usually follow a zone of weakness, such as a bedding plane
• Water tends to be channelled along these panes, increasing slippage
What is slumping?
• Occurs on weaker rocks (e.g. clay)
• Clay absorbs water, becomes saturated, and exceeds its liquid limit, so flows along a slip plane
What is creep?
• Individual soil particles are pushed/heaved to the surface by wetting, heating or freezing of water
• They move at right angles to the surface as it is the zone of least resistance
• Fall under the influence of gravity once the particles have dried, cooled or water has thawed
• Net movement is downslope
• Form terracettes
What factors affect the rate of mass movement?
• Slope angle
• Amount of regolith (loose material created by weathering)
• Amount of water present
• Amount of vegetation
• Rock type: water percolates less resistant rocks, it becomes saturated, pore pressure increases, pushes grains apart, = slump
• Climate: cliffs are heavier, increased lubrication encourages slides + slumps, wetting and drying, = mass movement
What landforms occur due to erosion?
• Wave cut platform
• Wave cut notch
• Cliffs (cliff retreat)
• Headlands and bays