Year 11 Coasts Flashcards
Where are waves generally larger
Larger in s.w than s.e because waves formed by wind blowing over the sea
How do waves break
The bottom of the waves touch the sand, slows down and topples over (the top of the wave)
Qualities of destructive waves
Short wavelength, high frequency 10-14 wpm
steep wave front
gains much height over 1m
How do destructive waves act and when and where are they found
Restricted swash, strong backwash
Plunges onto beach, doesn’t travel far up beach
Found in exposed bays, build up pebbled bays
more common in winter, high energy
Qualities of constructive waves
Long wavelength, low frequency 8-10 wpm
Gentle sloping wavefront
low wave height under 1m
How do constructive waves act and when and where are they found
Strong swash, weal backwash
Found in sheltered bays and spits where they build up sandy beaches. more common in summer
low energy
Process of coastal erosion
1.
Hydraulic action
air trapped in rocks or cliff face. when wave breaks, trapped air is compressed and weakens the cliff
Process of coastal erosion
2.
Abrasion
Bits of sand and pebbles carried in waves wear away at cliff face like sandpaper
Process of coastal erosion
3.
Attrition
Waves smash grinding down load particles. during transport, pebbles collide over time break into smaller pebbles
Process of coastal erosion
4.
Solution
Sea contains acids which dissolve rock causing it to wear away. sea water reacting with rock through chemical reaction
When does deposition occur
Low energy, sheltered bays
If a large source of sediment updrift
large expanses of beach
Engineered structures (groynes) trap sediment
What is mass movement
Shifting of rocks and loose material down a slope. happens when force of gravity greater than supporting force
What is rockfall
Fragments of rock break away from cliff face often due to freeze-thaw
What is a landslide
Blocks of rock slide downhill
What is a mudflow
Saturated mud, soil and weak rock flow downhill
What is rotational slip
Slump of saturated soil and weak rock along curved surface
What’s fetch
Distance wave travels across open water
What is backwash
Water flowing back into the ocean at a right angle to the beach
What are the three types of chemical weathering
Carbonation
Hydrolysis
Oxidation
What is Carbonation
Carbonic acid in rain water reacts with calcium carbonate so limestone carried away in solution
What is Hydrolysis
When acidic rain breaks down rock
What is Oxidation
When rocks are broken down by oxygen and water
What is Solution
When there is a change in chemical composition of the rocks
What are the two types of mechanical (physical) weathering
Freeze-thaw
Salt weathering
What is Freeze-thaw
Happens when water enters crack, freezes and expands putting pressure on rock. when melts, pressure relieved. continuous process leads to rock breaking
What is Salt weathering
When salt from sea gets in cracks, may evaporate and crystallize putting pressure on rock and weakening structure
What is biological weathering
As plant roots grow, they expand and push rock apart
Why is sediment deposited in coastal areas
When waves enter shallower water/sheltered water
When there’s little wind
When there’s a good supply of material
What’s a concordant coastline
Where the type of rock stays the same along the coastline. Tend to have fewer bays and headlands
What’s a disconcordant coastline
Where the geology alternates between strata (or bands) of hard and soft rock
How are headlands and bays formed
Hard (chalk) and soft (clay, sand, glacial till) rock
Bays form due to rapid erosion of softer rock
Headland left sticking out as resistant to erosion
What happens to the headlands and bays once they are formed
Bay becomes sheltered by headlands so less eroded
Headland left more vulnerable to erosion and wave energy is concentrated here
How are cliffs formed
between high and low tide rocks hurled at base of cliff- corrosion
creates wave-cut notch and top of cliff becomes unstable
overhang will collapse into the sea leaving a cliff
How are wavecut platforms formed
Material broken off from headland means more material for corrasion so the process will continue.
because there is no erosion below low tide, wave-cut platform is left.
How is a cave formed
Small lines of weakness in rocks. hydraulic action - crack widens causing small cave in headland
increased headland erosion due to wave refraction
Over time attrition, abrasion etc. causes cave deeper and wider
How is an arch formed
Process of cave continues to happen until eroded all the way through forming an arch
How are stacks and stumps formed
Arch weakened , by weathering so will collapse leaving a stack in its place. this will eventually form a stump
What is a spit
Long finger of sand or shingle jetting out into the sea from the land
How are spits formed
Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in longshore drift.
How are bars formed
When the spit meets a bay it continues from one headland to another forming a bar. where the old bay was is now a lagoon which will eventually be filled by deposition
What is a beach
Areas of deposited sediment- sand and shingle which have been deposited as currents and longshore drift have lost energy
Gradient, dominant waves, distance stretches back, back of beach of sandy beach
shallow almost flat, constructive, a long way, sometimes sand dunes
Other characteristics of a sandy beach
At low tide water fills depressions called runnels form. these are separated by small sandy ridges running parallel to the shore
Gradient, dominant waves, distance stretches back, back of beach of pebble beaches
Generally steep, destructive, not far, storm beach with large pebbles
Other characteristics of a pebble beach
Pebbles increase in size towards the back of the beach
What’s a berm
A terrace on a beach that’s formed in the backshore above the water level at high tide
formed in calm weather when constructive waves transport material onto the beach
What is needed for dune formation
Large flat beach with large sand supply
large tidal range
onshore wind
obstacle (drift wood or litter)
How are sand dunes formed
Wind blows sand and collects around obstacle forming embryo dunes
dunes begin to stabilise as colonised with plants holding the dunes together
these produce fore dunes and eventually yellow dunes
What happens over time with the yellow dunes
Rotting organic material makes sand more fertile allowing range of vegetation to exist
wind can form depressions where sands removed from dune, exposing water table below forming ponds called blowouts
mature dunes eventually form with more complex vegetation found
