3 Coastal systems and landscapes Flashcards
What are coasts?
They are natural systems - they have inputs, outputs, flows, stores of sediment and energy.
What is a negative feedback loop?
It is when a change in the system causes other changes that have the opposite effect. For example, as a beach is eroded, the cliffs behind it are exposed to wave attack. Sediment eroded from the cliffs is deposited on the beach, causing it to grow in size again.
What is a positive feedback loop?
It is when a change in the system causes changes that have a similar effect. For example, as a beach starts to form it slows down waves, which can cause more sediment to be deposited increasing the beach size.
How is wind created?
It is created by air moving from areas of high pressure to areas of low pressure. During events such as storms, the pressure gradient is high and winds can be very strong.
How are waves created?
Waves are created by the wind blowing over the surface of the sea. the friction between the wind and the surface pf the sea gives the water a circular motion. As waves approach the shore they break. Friction with the sea bed slows the bottom of the wave and makes their motion more elliptical. the crest of the wave rises up and then collapses.
What is the swash?
The movement of water up the beach.
What is backwash?
The movement of water back towards to sea.
What is a constructive wave?
They have a low frequency. They’re low and long which gives them a more elliptical cross profile. The powerful swash carries material up the beach and deposits it.
What is a destructive wave?
They have a high frequency. They’re high and steep, with a more circular cross profile. The strong backwash removes material from the beach.
What are tides?
Tides are periodic rise and fall of the ocean surface, caused by the gravitational pull of the Moon and the Sun.
What are currents?
A current is the general flow of water in one direction - it can be caused by wind or by variations in water temperature and salinity. Currents move material along the coast.
What are high energy coasts?
High-energy coasts receive high inputs in the form of large, powerful waves. These can be caused by strong winds, long fetches and steeply shelving offshore zones. They tend to have sandy coves and rocky landforms. the rate of erosion if often higher than the rate of deposition.
What are low energy coasts?
Low energy coasts receive low inputs of energy in the form of small, gentle waves. These can be caused by gentle winds, short fetches and gently sloping offshore zones. Some coastlines are low energy because there is a reef or island offshore, which protects the coast from the full power of the waves. They have saltmarshes and tidal mudflats. the rate of deposition is greater then the rate of erosion.
What is a sediment budget?
it is the differences between the amount of sediment that enters and the amount that leaves. If more enters than leaves, it’s a positive sediment budget and the coastline builds up. If more sediment leaves then enters, it’s a negative sediment budget and the coastline retreats.
What is a sediment cell?
The coast is divided into sediment cells. They are lengths of coastline that are pretty much entirely self-contained for the movement of sediment. This means that processes going on in one cell don’t affect the movement of sediment in another cell - each cell is a closed coastal system.
What is erosion?
It’s the action of removing material from one place to another.
What is corrasion (abrasion)?
Bits of rock and sediment transported by the waves smash and grind against rocks and cliffs, breaking bits off and smoothing surfaces,
What is hydraulic action?
Air in cracks in cliffs is compressed when waves crash in. The pressure is exerted by the compressed air breaks off rock pieces.
What is wave quarrying?
The energy of a wave as it breaks against a cliff enough to detach bits of rock.
What is solution (corrosion)?
Soluble rocks get gradually dissolved by the seawater.
What is attrition?
Bits of rock in the water smash against each other and break into smaller bits.
What is transportation?
the process of eroded material being moved.
What is solution (transportation)?
Substances that can dissolve are carried along the in the water.
What is saltation?
Larger particles, such as pebbles or gravel, are too heavy to be carried in suspension. Instead, the force of the water causes them to bounce along the sea bed.
What is suspension?
Very fine material, such as silt and clay particles, is whipped up by the turbulence and carried along in the water. Most eroded material is transported this way.
What is traction?
Very large particles, e.g. boulders, are pushed along the sea bed by the force of the water.
How does longshore drift (LSD) occur?
Swash carries sediment up the beach, parallel to the prevailing wind. Backwash carries sediment back down the beach, at right angles to the shoreline. When there’s an angle between the prevailing wind and the shoreline, a few rounds of swash and backwash move the sediment along the shoreline.
What is sub-aerial weathering?
It is the gradual breakdown of rock by agents such as ice, salt, plant roots and acids. It weakens cliffs and makes them more vulnerable to erosion.
What is salt weathering?
Salt weathering is caused by saline (salty) water. This saline water enters pores or cracks in rocks at high tide. As the tide goes out the rocks dry and the water evaporates, forming salt crystals. As the salt crystals form they expand, exerting pressure on the rock - this causes pieces to fall out.
What is freeze-thaw weathering?
Freeze-thaw weathering occurs in areas where temperatures fluctuate above and below freezing. Water enters the joints and crevices in rocks. If the temp drops below 0, the water in the cracks will freeze and expand. Over time, repeated freeze-thaw action weakens the rocks and causes pieces to fall off.
What is chemical weathering?
Chemical weathering is the breakdown of rock by changing its chemical composition. For example, carbon dioxide in the atmosphere dissolves in rainwater, forming a weak carbonic acid. This acid reacts with rock that contains calcium carbonate, so the rocks gradually dissolved.
What is mass movement?
Mass movement is the shifting of material downhill due to gravity. in coastal areas, it is mostly likely to occur when cliffs are undercut by wave action - this causes an unsupported overhang which is likely to collapse.
What are examples of mass movement?
Slides - material shifts in a straight line,
Slumps - material shifts with a rotation,
Rockfalls - material breaks up and falls,
Mudflows - material flows downslopes.
How are cliffs an wave-cut platforms made?
Cliffs form as the sea erodes the land. Over time, cliffs retreat due to the action of waves and weathering. Weathering and wave erosion cause a notch to form at the high water mark. This develops a cave. Rock above the cave becomes unstable with nothing to support it, and collapses. Wave-cut platforms are flat surfaces left behind when a cliff is eroded.
How are headlands and bays formed?
Headlands and bays form where there are bands of alternating hard rock and soft rock at right angles to the shoreline. The soft rock erodes quicker, forming a bay. The harder rock is eroded less and sticks out as a headland.
How are caves, arches and stacks formed?
Weak areas in rock are eroded to form caves. Caves on the opposite sides of a narrow headland may eventually join up to form an arch. When an arch collapses it forms a stack.
How are beaches formed?
Beaches form when constructive waves deposit sediment on the shore. Shingle beaches are steep and narrow. They’re made up of larger particles, which pile up at steep angles. Sand beaches, formed from smaller particles, are wide and flat. Beaches have distinctive features, berms are ridges of sand and pebbles found at high tide marks. Runnels are grooves in the sand running parallel to the shore, formed by backwash draining to the sea. Cusps are crescent-shaped indentations that form on beaches mixed sand and shingles.
How are spits formed?
Spits form when the coast suddenly changes direction.
Longshore drift continues to deposit material across the river mouth, leaving a bank of sand and shingle sticking out into the sea. A straight spit that grows out roughly parallel to the coast is called a simple spit. Occasional changes to the dominant wind and wave direction may lead to a spit having a curved end. Serval recurved ends may be abandoned as the waves return to their original direction. If a spit has many recurved ends resulting from serval periods of growth is called a compound spit. the area behind the spit is sheltered from the waves and often develops into mudflats and saltmarshes.
How are bars formed?
Bars are when 2 spits join 2 headlands together across a bay or river mouth. A lagoon forms behind the bar. They also form off the coast when material moves towards the coast. These may remain partly submerged by the sea - this becomes an offshore bar.
How is a tombolo formed?
A bat that connects the shore to an island (often a stack) is called a tombolo.
