1.B - influences on the coastal landscape Flashcards
how does wind influence the coastline?
The wind is able to shape the coastline in 2 ways:
1. frictional drag that is has on the surface of the ocean is able to create waves which are capable of carrying out coastal marine erosion, transport and deposition.
- the wind direction will have a strong influence on wave direction and wind strength should have an effect on wave height.
2. - the wind itself is able to carry out erosion, transportation and deposition.
- these processes combine to create aeolian landforms, such as coastal dunes.
what is the WAVE LENGTH?
the distance from crest to crest
what is the wave crest?
the highest point of the wave
what is the wave trough?
the lowest point of the wave
what is the wave height?
the vertical distance from trough to crest
what is swash?
the movement of water up a beach after a wave has broken
what is backwash?
the flow of water down a beach after a wave has broken
what is a SPILLING BREAKER WAVE?
- they occur as waves travel across a gently sloping bottom (i.e. near the beach).
- the wave breaks long and slow, losing its energy as white water spilling from the crest down the front of the wave.
- water spills gently forward as the wave breaks
what is a PLUNGING BREAKER WAVE?
- occur as waves approach moderate to steep sea bottoms.
- the wave becomes steeper than a spilling breaker
- the crest falls as a well defined curve, falling forward with considerable energy
- strong backwash, making them more destructive
what is a SURGING BREAKER WAVE?
- low angle waves breaking onto steep beaches
- the wave slides forward and may not actually break
what is fetch?
the distance of open water in 1 direction from a coastline, over which the wind can blow.
how are waves created?
- waves are created by the wind blowing over the surface of the water,
- out to sea this creates OSCILLATION WAVES which will have no forward momentum of water, only energy is transferred forward,
- the wave height depends on the strength and duration of the wind, the depth of the water and the length of the fetch
what does wave height depend on?
the wave height depends on:
- the strength and duration of the wind
- the depth of the water and
- the length of the fetch
what is a swell wave?
- this is the name for the waves generated out at sea.
- they have long wavelength and a wave period of up to 20 secs
- this contrasts against locally produced storm waves, which have a greater wave height, shorter wavelength and wave period.
what are the characteristics of a CONSTRUCTIVE WAVE?
- low in height
- long wavelength
- low frequency (typically 6-8 per min)
- break as spilling waves and strong swash travels a long way up the gently sloping beach
- due to long wavelength, backwash returns to the sea before the next wave breaks, so the next swash movement is UNINTERRUPTED, and thus retains its energy
- a key feature is that (therefore) swash energy exceeds backwash energy.
what are the characteristics of a DESTRUCTIVE WAVE?
- greater height
- shorter wavelength
- higher frequency (12-14 per min)
- break as plunging waves so there is little forward transfer of energy to move water up the steeply sloping beach as swash.
- friction from the steep beach slows the swash so it doesn’t travel far before returning down the beach as backwash
- with a short wavelength, the swash of the next wave is often slowed by the frictional effects of meeting the returning backwash of the previous wave
- swash energy is LESS that backwash energy.
what are aeolian processes?
any landform shaped by WIND
what is wind’s effect on the coastal landscape?
- the source of energy for coastal erosion and sediment transport is wave action.
- this wave energy is produced through the frictional drag of wind across the oceans surface.
- THE HIGHER THE WINDSPEED AND THE LONGER THE FETCH, THE LARGER THE WAVES AND THE MORE ENERGY THEY POSSESS.
how does the direction of wind influence the coastline?
- onshore winds, blowing from the sea towards the land, are particularly effective at driving waves towards the coast.
- if wind blows at an oblique angle to the coast, the resultant waves will also approach obliquely and generate long shore drift.
what is wind?
- wind is a moving force and as such is able to carry out erosion, transportation and deposition itself.
- these aeolian processes contribute to the shaping of many coastal landscapes.
what is the significance of wind energy?
- overall not very significant
- wind could be considered significant as it is responsible for the strength, severity and direction of waves.
- wind causes friction on the sea surface causing waves; the greater the fetch the bigger the waves.
- the significance of wind CHANGES FROM DAY TO DAY MAKING IT A TEMPORAL FACTOR.
how do aeolian processes and the succession of plants work together to create dune complexes?
- at low tide, incoming solar radiation (input of energy) is able to dry the sand out.
- as the wind blows over the sand it is able to erode it by processes of deflation (erosion of clay and silt-sized particles by wind action in dry lands).
- dry sand is much easier for wind to pick up than wet sand, as moisture increases cohesion between particles to help them stick together.
- plant roots help to build up and stabilise sand (e.g. prickly saltwort.)
- pioneer plant species are zerefite (well adapted)
- e.g. they don’t lose water as easily by transpiration due to waxy leaves / deep roots to access nutrients.
- plants act as a shield.
what is a concordant coastline?
a coastline with bands of different geologies lying PARALLEL to the shore.
what is a discordant coastline?
- rock strata lies at right angles to the coast.
- deep bays and pronounced headlands produced.
- more resistant rocks form headlands, weaker rocks form bays.
what is the angle of dip?
the angle of the strata (layers) in sedimentary rocks when compared to the horizontal.
what types of current are there?
- currents can either be local currents such as rip currents or tidal currents
- or much larger ocean currents such as the North Atlantic Drift
what are ocean currents?
large scale phenomena that are generated by convection from the Earth’s rotation
how do rip currents form?
- caused by tidal motion or by waves breaking at right angles to the shore.
- water from the top of breaking waves with a large height travels further up the shore and then returns through the adjacent area where the lower height waves have broken.
what impact do rip currents have on coastlines?
- once rip currents have formed, they modify the shore profiles
- by creating cusps
- which help perpetuate the rip current, channelling flow through a narrow neck.
how do warm and cold ocean currents alter UK coastlines?
- warm ocean currents transfer heat energy from low latitudes towards the poles.
- they change the temperature of water, (alters the amount of freeze-thaw weathering), which affects weathering processes and input of sediment to a system.
- cold currents do the opposite (towards the equator) which therefore results in less effect on our coastlines.
what causes tides?
- The moon pulls the water towards itself, creating a HIGH TIDE, and there is a compensatory bulge on the other side of the earth.
- At locations between the two bulges, there will be a LOW TIDE.
- As the moon orbits the earth, the high tides follow it.
- The highest tides will occur when the moon, sun and earth are all aligned and so the gravitational pull is at its strongest.
- On a more local level, tides are controlled by the geomorphology of the sea bed and shape of the coastline.
what are tides?
- the periodic rise and fall of the sea’s surface
- that are caused by the gravitational pull of the moon and (to a lesser extent) the sun
what is tidal range?
the vertical difference in height between consecutive high and low waters over a tidal cycle.
what influence do tides have on the coastline?
- Tides determine the position at which the waves break on the beach, but also the range over which wave action can occur.
- In enclosed seas, such as the Mediterranean, tidal ranges are low and so wave action is restricted to a narrow area of land.
- In places where the coast is funnelled, such as the Severn Estuary, tidal range can be as high as 14m.
- The tidal range, therefore, influences where wave action and coastal processes can occur.
- A small tidal range leads to erosional processes dominating.
- A large tidal range leads to depositional processes dominating.
what are spring tides?
- The highest tides will occur when the moon, sun and earth are all aligned and so the gravitational pull is at its strongest.
- This happens twice each lunar month and results in SPRING TIDES with a high tidal range.
what are neap tides?
twice a month, the moon and the sun are at right angles to each other and the gravitational pull is therefore weakest, producing NEAP TIDES with a low range
what are tides controlled by on a local level?
tides are controlled by the geomorphology of the sea bed and shape of the coastline.
why does the tidal range vary across the planet?
- shape of coastlines change
- oceans are able to have a bigger difference
how will having a large tidal range affect coastal processes/landforms?
- large tidal ranges results in more deposition
- tidal range influences where wave action occurs, the weathering processes that happen on land exposed between tides and the potential scouring effect along coasts with a high tidal range.
- deposition is dominant and creates a greater number of estuaries
how will having a small tidal range affect coastal processes/landforms?
- smaller tidal ranges result in more erosion due to the fact the waves are hammering a smaller area more often and with more force
- wave energy is concentrated in a smaller area
what does tidal range influence?
the level of weathering
