COASTS
Waves
Fetch: distance of open sea over which wind has blown (greater fetch = larger wave)
What a ects wave height? Fetch, wind strength
Wave going up beach = swash
Wave going down beach = backwash
Constructive -> swash is greater than backwash (depositional wave)
-> long length, short height
-> gentle
Destructive -> backwash is greater than swash (erosional wave)
-> short length, steep height
-> form frequently
Erosion
-> most erosion with destructive waves + weak coastline
Hydraulic Action: power of the sea/waves can wash away soft rock, or air can be trapped in
crevices of cli s when waves break against it, this compressed air forces cracks to widen
Abrasion: breaking waves hurl sand/pebbles at cli s which wear them away or undercut
Attrition: particles are swirled around by waves, hit against each other + become smaller and
more rounded
Corrosion: acidic sea water dissolves away rocks or cli s, especially limestone
Transportation
Longshore drift: prevailing wind means waves hit beach at an angle, swash moves up beach at
this angle but backwash draws straight (at right angles to coast), over time material is transported
along the coast
Deposition
-> material is dropped by constructive waves usually in summer when light winds to form
beaches/spits/sand dunes
Erosional landforms
How do headlands form? Sections of cli which are made from hard, more resistant rock are
less easily eroded (HA + AB) + stick out to form headlands
How do cli s + wave cut platforms form?
-> destructive waves attack base of cli by HA and AB ( between high + low water marks)
-> weakest parts erode to from a notch
-> notch is eroded + cli s undercut until they lose support + collapse
-> this repeats + cli retreats backwards
-> leaving an area of at rock at low water mark (wave cat platform)
Example: Cloonagh, Co. Sligo
How are caves/arches/stacks/stumps formed?
-> wave cut notch enlarges into a cave on either side of headland (HA + AB)
-> further erosion causes caves to erode through headland + form an arch
-> sea keeps eroding so that arch roof cannot hold up + collapses
-> leaving an isolated stack (stack can be undercut to leave a stump)
Example: Old Harry Rocks, Dorset
Depositional landforms
How do beaches form?
In area between high + low tide sand/single etc is deposited by constructive waves which build
up = beach, they are good defences against erosion
Sandy beaches = gentle sloping Shingle = steep beach
How do spits form?
-> spit is an area of sand that extends out from mainland into sea
Needs: LSD operates most of time, sea is quite shallow, change in direction of coastline (leaving
sheltered area), constant supply of sand/material from further up coast
* explain longshore drift
-> when material being moved reaches a natural break in coastline sand continues to be
deposited in shallow water sheltered by headland = forms spit attached to headland
-> spit may become hooked if angle of wave changes as spit extends into estuary + it curves
Example: Spurn Head, England
ff ff ff ff fl ff ff ff ff ff
Waves
Fetch: distance of open sea over which wind has blown (greater fetch = larger wave)
What a ects wave height? Fetch, wind strength
Wave going up beach = swash
Wave going down beach = backwash
Constructive -> swash is greater than backwash (depositional wave)
-> long length, short height
-> gentle
Destructive -> backwash is greater than swash (erosional wave)
-> short length, steep height
-> form frequently
Erosion
-> most erosion with destructive waves + weak coastline
Hydraulic Action: power of the sea/waves can wash away soft rock, or air can be trapped in
crevices of cli s when waves break against it, this compressed air forces cracks to widen
Abrasion: breaking waves hurl sand/pebbles at cli s which wear them away or undercut
Attrition: particles are swirled around by waves, hit against each other + become smaller and
more rounded
Corrosion: acidic sea water dissolves away rocks or cli s, especially limestone
Transportation
Longshore drift: prevailing wind means waves hit beach at an angle, swash moves up beach at
this angle but backwash draws straight (at right angles to coast), over time material is transported
along the coast
Deposition
-> material is dropped by constructive waves usually in summer when light winds to form
beaches/spits/sand dunes
Erosional landforms
How do headlands form? Sections of cli which are made from hard, more resistant rock are
less easily eroded (HA + AB) + stick out to form headlands
How do cli s + wave cut platforms form?
-> destructive waves attack base of cli by HA and AB ( between high + low water marks)
-> weakest parts erode to from a notch
-> notch is eroded + cli s undercut until they lose support + collapse
-> this repeats + cli retreats backwards
-> leaving an area of at rock at low water mark (wave cat platform)
Example: Cloonagh, Co. Sligo
How are caves/arches/stacks/stumps formed?
-> wave cut notch enlarges into a cave on either side of headland (HA + AB)
-> further erosion causes caves to erode through headland + form an arch
-> sea keeps eroding so that arch roof cannot hold up + collapses
-> leaving an isolated stack (stack can be undercut to leave a stump)
Example: Old Harry Rocks, Dorset
Depositional landforms
How do beaches form?
In area between high + low tide sand/single etc is deposited by constructive waves which build
up = beach, they are good defences against erosion
Sandy beaches = gentle sloping Shingle = steep beach
How do spits form?
-> spit is an area of sand that extends out from mainland into sea
Needs: LSD operates most of time, sea is quite shallow, change in direction of coastline (leaving
sheltered area), constant supply of sand/material from further up coast
* explain longshore drift
-> when material being moved reaches a natural break in coastline sand continues to be
deposited in shallow water sheltered by headland = forms spit attached to headland
-> spit may become hooked if angle of wave changes as spit extends into estuary + it curves
Example: Spurn Head, England
ff ff ff ff fl ff ff ff ff ff
