Sources Of Energy Wind/wave/currents/tide Flashcards
Why is wind so significant?
It is a primary source of energy for other processes, important agent for erosion and transport itself.
Higher / uninterrupted wind will create what kind of waves ?
Higher energy waves
Destructive
Prevailing wind direction
Wind reaching coast from one direction.
Which is important as this controls direction that waves approach coastline and also direction of transport of material in coastal zone.
Fetch
Refers to the distance of pen water which wind blows uninterrupted by land obstacles.
Length of fetch helps determine magnitude and energy of waves
How does wind create waves?
Waves are created by transfer of energy from the wind blowing over the sea surface “frictional drag”
Energy acquired by waves depends upon strength of wind and length / time it’s blowing and the fetch.
How does wind act as an agent of erosion ?
Pick up and remove sediment from coast and use this to further erode other features.
Abrasion is the most common type of wind erosion - wind carries material wearing away landscape
Why are waves significant?
They shape the coastline
WAve height
Difference between wave crest and neighbour trough
Wave length
Distance been 2 successive crests
Wave frequency
Time for 1 wave to travel the distance if one wave length
What happens when waves approach shallow water ?
Friction with seabed increases and the base of the wave begins to slow down.
Increases height / steepness of wave until upper part plunges forward and wave breaks Onto shore
Rushes up beach as swash and any water running back down beach is backwash.
Characteristics of constructive waves
Low wave height
Long wavelength -100m
Low frequency 6-8 per min
As approach beach the wave front steepens slowly giving gentle spill.
Swash is larger than backwash as swash loses volume / energy percolating into beach material.
Weak backwash means not much material is pulled back.
Constructive waves and beach material
Strong swash and weak back wash means material is slowly but constant moves up beach leading to formation of berms
Built beach up
Characteristics of destructive waves
High wave height
Steep form / beach profile
High frequency 10-14 per min
As they approach beach they rapidly steepen and break plunging down creating power backwash as there is little swash
Destructive waves as material
Very little material moved up beach as backwash pulls material down.
Storm beach
When shingle goes towards rear of the beach forming large ridges
Cycle of waves
Constructive waves build up beach and result in steeper beach profile.
This encourages destructive waves to occur as they’re associated with more steeper beach profile.
With time destructive waves move material back towards the sea reducing the beach angle and encouraging more constructive waves.
Negative feedback - maintains equilibrium
What happens when waves approach an irregular shaped coastline.
They become refracted and increasingly parallel to coast.
When they meet shallow water around headland waves increase in height as speed decreases.
Wave in deep water moves forward faster, causing wave to bend.
Energy concentrated on headland causing greater erosion.
Low energy waves concentrated in bay resulting in sheltered area and deposition occurring.
May be slight local rise in sea level due to piling of waves against headland which results in longshore currents from headland - moving material to bay leading to build up of beaches.
Define current
Permanent / seasonal movement of surface water in seas and oceans
Longshore current
RIP current
Upwelling
Longshore currents
Waves don’t hit coastline heady on but approach at an angle to shoreline
Generates flow of water running parallel to shoreline.
Transports sediment parallel to shoreline
RIP currents
Strong currents moving away from
Shoreline
Pile up of incoming waves.
Hazardous to boats/ swimmers
Upwelling
Movement of cold water from deep in ocean towards surface
Dense cold water replaces warmer surface water and creates nutrient cold rich currents
Define tides
Periodic rise and fall in the level of the sea by gravitational pull of the sun and moon
Spring tide
Moon orbits earth
Twice in a lunar month when moon/ earth / sun are in straight line the tide raising force is strongest.
Highest month tidal range / SPRING TIDE.
Neap tide
Twice a month
The moon and sun positioned at 90 degrees to each other in relation to earth.
Lowest monthly tidal range /NEAP TIDE.
High/ low tides are 10-30% lower than average
Who has greater influence on tide ?
Moon as it’s nearer
Moon pulls water towards it.
How is tide different in individual locations ?
Morphology of sea bee
Proximity of land masses
Spinning force of earth
Tidal range
Tidal range
Different in height of sea water at high and low tide.
what do tidal ranges determine?
Upper and lower limits of erosion / deposition.
And amount of time each day that the littoral zone is exposed and open to sub aerial weathering
Example low tidal ranges
Mediterranean Sea
Example of high tidal range
British isles
Erosional land scales like wave cut platforms
Tidal/ storm surge
Meteorological conditions give rise to sting winds producing higher water levels than those at high tide
Eg North Sea
High energy coast
strong / steady / prevailing winds create high energy waves
Erosion exceeds deposits
Headlands / cliff
N. America
N. Cornish coast
Low energy coast
Wave energy is low and not as strong winds.
Deposition exceeds Erosion
Beaches / spits
Estuaries / inlets
The Baltic Sea
