Flashcards in how do characteristics coastal landforms contribute to coastal landscapes? Deck (34)
what are some factors that contribute to the shape and features of a coastal landscapes?
-WAVE TYPES and erosion processes are important in terms of the production of coastal landscapes
-LONG SHORE DRIFT/sediment transport and deposition produce coastal landforms, often stabilised by coastal succession.
-weathering and mass movement SUBAERIAL PROCESSES are important on coastlines
-GEOLOGY and lithology/rock types and sediments
how are waves formed?
waves are caused by friction between wind and water transferring energy from the wind to the water. The force of the wind blowing on the surface of the water generates ripples, which grow into waves when the wind is sustained.
what does the wave size depend on?
-strength of wind
-the duration the wind blows for
-wave fetch (uninterrupted distance across water over which a wind blows and therefor the distance waves have to grow increases in size)
how does a wave break?
waves break as the water depth shallows towards a coastline
-at a water depth of approximately half the wavelength, the internal orbital motion of water within the wave touches the sea bed
-this creates friction between the wave and the sea bed, slowing down the wave
-as the wave approaches the shore, wavelength decreases and wave hight increases so waves 'bunch' together
-the wave crest begins to move forward much faster than the wave trough
-eventually the wave crest outruns the waves trough and the wave topples forward (breaks)
what is the difference between constructive and destructive waves?
constructive waves have a strong swash. they spill into the beach and push sediment up the beach. they have a low wave height (less than 1m) and long wave length (up too 100m)
destructive waves have a strong backwash. the wave plunges and thus sediment is eroded and then deposited offshore. (have a wave height of 1m and a wavelength of 20m).
what is beach morphology?
the shape of the beach, including its width and slope (beach profile) and features such as berms, ridges and runnels. it also includes the type of sediment (shingle sand and mud) found at different locations on the beach.
when can significant changes to beach morphology occur?
- when a storm passes and constructive waves turn to destructive waves causing erosion
-between summer and winter
-changes in climate (uk will become more stormy due to global warming)
what are the four marine erosional processes?
-Hydraulic action (air trapped insects cracks and fissures is compressed by waves crashing against the rock face. pressure forces cracks to open meaning more air is trapped. this process continues until rock is broken away from the cliff face.
-Abrasion (sediment picked up by breaking waves in thrown against the cliff which chisels away at the surface and gradually wears it down.
-Attrition (as sediment is moved around by waves, the numerous collisions between particles slowly chip fragments off the sediment, making it smaller and more rounded over time.
-Corrosion/solution (carbonated rocks (limestone) are vulnerable to solution by rainwater, spray from the sea and seawater.
describe a wave cut notch process
-the cliff face is eroded at the base by hydraulic action and abrasion which forms a wave-cut notch
-as the notch becomes deeper, the overhanging rock above becomes unstable and eventually collapses as a rock fall
-repeated cycles of notch-cutting and collapse causes the cliff to recede inland
what are the four types of sediment transport processes?
-Traction (sediment rolls along, pushed by waves and currents)
-Saltation (Sediment bounces along, either because of the force of water and wind)
-Suspension (Sediment is carried in the water column)
-Solution (Dissolved material is carried in the water as solution).
what is longshore drift and describe the process
waves approach at a 38º to the beach and move sediment up. the wave then retreats at a 90˚ angle and bring the sediment down with them in their backwash. this continued zig-zag motion allows for sediment to move up the beach.
what are the two main ways deposition can occur?
1. gravity settling occurs when the energy of transporting water becomes too low to move sediment. Large sediment will be deposited first, followed by smaller sediment (pebbles>sand>silt)
2. Flocculation is a depositional process that is important for very small particles such as clay, which are so small they will remain suspended in water. Clay particles clump together through electrical or chemical attraction, and become large enough to sink
name 6 key depositional landforms?
how is a spit formed?
Spits are formed where the coast suddenly changes direction e.g. across a river mouth. Longshore drift continues to deposit material across the mouth of a river which results in the formation of a long bank of sand and shingle. At the turn of over 30°, the longshore drift current spreads out and loses energy, leading to deposition. The length of a spit is determined by the existence of secondary currents causing erosion, either the flow of a river or wave action which limits its length.
how do bay head beaches form?
Headlands are formed when the sea attacks a section of discordant coast with alternating bands of hard and soft rock. The bands of soft rock, such as sand and clay, erode more quickly than those of more resistant rock, such as basalt. This leaves a section of harder rock jutting out into the sea called a headland.
Through wave refraction, erosion is concentrated at headlands and the bay is an area of deposition.
what are tombolo's and how do they form?
a sand or shingle bar that links the coastline to an offshore island
tombolos form as a result of wave refraction around an offshore island which creates am area of calm water and deposition between the island and the coast. Opposing longshore currents may play a role, in which case the depositional feature is similar to a spit.
what are barrier beaches/bars and how do they form?
a sand or shingle beach connecting two areas of land, with shallow-water lagoon behind. These features form when a spit grows so long that it extends across a bay, closing it off.
what are hooked/recurved beaches and how do they form?
a spit who's end is curved landward, into a bay or inlet.
the seawater (distal) end of the spit naturally curves landward into shallower water and the hook may be more pronounced by waves from secondary direction to the prevailing wind.
what are cuspate forelands and how do they form?
roughly triangular shapes features extending out from a shoreline. there is some debate about their formation, but one hypothesis suggests they result from the growth of two spits from opposing longshore drift directions.
in what way do coastlines operate as sediment systems consisting of three interlinked components?
1. sources: places where sediment is generated, such as cliffs or eroding sand dunes or offshore bars and river systems
2. Transfer zone: places where sediment is moving alongshore through LSD and offshore currents
3. Sinks: locations where the dominant process is deposition and depositional landforms are created, including spits and offshore bars.
how do the coastlines sediment systems operate?
in the case of a storm, the systems equilibrium may be disrupted due to a spit being heavily eroded. however over time, the system tends to maintain a balance by pushing the system back to one.
e.g large amount of cliff may collapse, but the rock debris at the base of the cliff will slow down the erosion by protecting the cliff from wave attack.
what are subaerial processes?
A combination of weathering and mass movement processes that alter the shape of a coastline.
what is weathering?
is the situ breakdown of rocks by chemical, mechanical or biological agents. It does not involve any movement.
what are the three types of weathering?
mechanical: breaks down rock by the exertion of a physical forced does not involve any chemical change
chemical: involves a chemical reaction and the generation of new chemical compounds.
biological: often speeds up mechanical or chemical weathering through the action of plants, bacteria or animals
what does lithology mean?
the technical term for different rock types and the general physical characteristics of rocks.
what are the two types of mechanical weathering?
which rocks are vulnerable?
FREEZE-THAW: water expands by 9% in volume when it freezes, which exerts a force within cracks and fissures; repeated cycles of this weakens and loosens the rock causing it to break.
vulnerable: any rocks with cracks, joints or fissures.
SALT CRYSTALLISATION: the growth of salt crystals in cracks and pore spaces that exert a breaking force, although less than freeze-thaw.
vulnerable: porous and fractured rock e.g sand stone. greater in hot dry climates as it encourages the evaporation and precipitins of salt crystals.
what are the three types of chemical weathering?
which rocks are vulnerable?
CARBONATION: the slow dissolution of limestone due to rainfall producing calcium biocarbonate in solution
vulnerable: limestone and other carbonate rocks
HYDROLYSIS: the breakdown of minerals to form new clay minerals, plus materials in solution, due to the effect of water and dissolved carbon dioxide
vulnerable: igneous and metamorphic rocks containing feldspar and other silicate minerals
OXIDATION: the addition of oxygen to minerals especially iron compounds, which produces iron oxides and increases the volume contributing to mechanical breakdowns.
vulnerable: sandstone, siltstone and shales often contains iron compounds which can be oxidised
what are two types of biological weathering?
which rocks are vulnerable
PLANT ROOTS: trees and plant roots grow in cracks and fissures forcing rocks apart
vulnerable: an important contribution to vegetation on cliff tops which can encourage rock fall
ROCK BORING: species of clams or molluscs that bore into rock, and may also secrete chemicals that dissolve rocks.
vulnerable: sedimentary rocks, especially carbonate rocks (limestone) located in the inter-tidal zone.
what is meant by mass movement?
the downslope movement of rock and soil. It id an umbrella term for a wide range of specific movements including landslides, rockfalls and rotational slides.