Coastal - lithosphere Flashcards
factors which shape the coastal landscape:
- waves
- types of waves
- tides
- geological structure
- lithology
- weather & climate
- human; pollution, erosion and conservation
waves
the fetch s the maximum distance travelled by the wind over an area of water to create the waves
tides
- formed as a result of gravitational effect of the moon and the sun
- depend upon the position of the moon and the sun in relation to the oceans as the earth rotates
- the moon and sun’s gravity pulls the water beneath, until it forms mounds (higher water levels) which result in high tides
2 different types of waves
- spring tides: when the moon and sun act together, pulling from the same side, tides become higher than normal
- neap tides: when the moon and sun are on opposite sides, their counteraction results in lower than usual high tides
Lithology
some rock types may be more resistant to erosion than others and those with weaknesses will be more susceptible to particular types of erosion
weather and climate conditions
prevailing wind and regular or infrequent storms can influence the regularity and strength of waves approaching the coastline
Geological structure
- some cliffs formed in layers which slope in towards the land, others slope towards the sea (rocks will easily fall into the sea following erosion)
- layers of resistant and less resistant rocks, alternating mass movement (landslides) are likely ( less resistant rock is worn away leaving little support for rock above)
2 different types of rocks in the coastline
- Concordant: if the coastline has the same type of rock running parallel to the sea, very few bays and headlands due to erosion
- Discordant: where bands of different rock types run perpendicular to the coast, bays and headlands due to different rates of erosion
Types of waves
- constructive wave: low flat wave spills over, strong swash, weak backwash, gentle slope, low frequency of wave approach, circular motion of water is altered to elliptical due to frictional contact with seabed
- Destructive wave: wave plunges downwards, beach cliff forms, weak swash, strong backwash, steep slope, steep wave crest and shape due to sudden increase of friction at the waves base, high frequency of waves approach
main processes of coastal erosion
- ABRASION: waves pick pieces of rock as they travel, rocks are smashed against cliffs and headlands (in stormy conditions), erodes them and pieces break off
- HYDRAULIC ACTION: waves pound against cliffs and headlands, they drive air into weaknesses (little cracks), weakens rock further and pieces will break off
- SOLUTION: acids in the seawater slowly weaken and dissolve the rock that forms cliffs and headlands, limestone rock
- ATTRITION: erosion of pebbles and rocks that are carried by waves. forms sand and shingle, causes them to bash off and grind against each other
- WAVE POUNDING: exert shock waves of up to 30 tonnes/m2 and smash off pieces of rock, sub-process of hydraulic action, expresses the brute strength of the power of waves
Features of coastal erosion
- weaknesses
- cave
- arch
- stack
- needle
- stump
- geo’s
- seacaves
- blowholes
- wave cut platform
Stages of coastal erosion
Sea cave formation is the starting point
1- cave erodes from one side to the other
2- continued wave erosion expands and enlarges the arch
3- removal of the rock below makes the keystone unstable and it collapses
4- headland is now detached from the other side, remains as a pillar of rock (stack)
5- continued wave erosion and weathering may sharpen the stack to form a needle shape
6- wave erosion lower down the stack/needle; between low and high water; needle collapses leaving a small low-lying rock - stump
Which kind of rock leads to more erosion?
less resistant (bays)
Which kind of rock leads to less erosion?
hard resistant rock (headlands)
Where do Geo’s occur?
where waves have eroded along a weakness inland in a similar manner to sea caves
