Coasts key terms Flashcards
Wavelength
The distance between two successive crests
Wave frequency
Number of waves per minute
Wave crest
Highest point of a wave
Wave trough
Lowest point of a wave
Wave steepness
The ratio of the wave height to the wavelength
Wave period
The time taken for a wave to travel between one wavelength
Wave energy
A product of wind velocity, duration and fetch
Fetch
The distance the wind blows over the sea - the bigger fetch, the bigger wave
Erosion
EROSION IS THE WEARING DOWN OF ROCK BY MOVING FORCES - usually occurs at the base of our cliffs and by waves.
Weathering
WEATHERING IS THE WEARING DOWN OF ROCK ‘IN SITU’ BY ITS ENVIRONMENT - Sub aerial forces (like rain, air and temperature)
Mass movement
MASS MOVEMENT IS THE MOVEMENT OF ROCK DOWNHILL UNDER GRAVITY
Freeze thaw
Water repeatedly freezes and melts within rock joints in areas - as water freezes it expands and puts pressure on the rock, until it shatters
Pressure release
Overlying soil or regolith is removed, this pressure release can open joints in underlying rock
Biological weathering
Organic agents (trees, animals) grow and burrow into rock.
Chemical weathering
Occurs where there is alternate wetting and drying of an area which leads to a chemical reaction or breakdown of the cliff face.
Mechanical weathering
Takes place when rocks are broken down without any change in the chemical nature of the rocks
Soil creep
Top soil moves downslope under gravity - Wet and thawing periods add moisture and weight which increases creep
Solifluction
When an area begins to thaw, after a period of extended permafrost, the top soils can slide downslope as a whole layer
Mudflows
Heavy rainfall saturates ground on steeper slopes and unconsolidated soils flow downslope
Rockfalls
Rapid falling of rock/debris down very steep slopes or cliffs, rocks weakened by chemical weathering
Runoff
Surface runoff has ability to move soil and debris down slope - Particularly vulnerable are areas with little vegetation.
Slides and slumps
Slides and slumps maintain the structure of the strata of soil and rocks as they rotate and slip along weak fissures
Hydraulic action
Erosion of the cliffs caused by the force of water and air in the waves colliding against them
Abrasion
Erosion of the cliffs as waves throw particles and rocks against them.
Attrition
Erosion of the material carried in the waves. The material in the waves is smoothed as it bumps into each other
Solution (erosion)
Erosion of the cliffs by the salts and acids in seawater. Salts and acids are able to dissolve some rocks
Solution (transportation)
Minerals are dissolved in the water and carried along in solution.
Suspension
Fine light material is carried along in the water
Saltation
Small pebbles and stones are bounced along the river bed
Traction
Large boulders and rocks are rolled along the river bed
Deposition
The dumping of sediment by the sea - occurs when the waves lose energy
Offshore
Beyond the influence of the waves
Nearshore
Where the friction with the seabed causes the waves to slow and begin to break
Foreshore
The zone of constant change - swash and backwash operate here - Littoral drift occurs - Berms, ridges and runnels are created
Backshore
Affected by the spring high tides that deposits larger calibre sediment here
Eustatic sea level rise
Sea level change caused by change in volume due to ice caps melting
Isostatic sea level rise:
Sea level change caused by change of weight as ice melts on land
Postglacial rebound
Ice physically pushes land down (glacial subsidence)- when ice melts, the land bounces/rebounds back up
Example of sea level rise case study
Tuvalu, Polynesian Islands
Example of hard engineering shoreline management plan
Lyme Regis, Jurassic Coast
Example of soft engineering shoreline management plan
North Norfolk
Example of headlands and bays
Swanage Bay, Dorset
Discordant coast line
Example of a cliff, wave cut notches and platforms
Burgh Island, Devon
Example of Cracks, Caves, Arches, Stacks and Stumps
Old Harry rocks
Example of a spit
Spurn Head, Holderness Coast
Example of a bar
Slapton sands, Devon
Example of a tombolo
Chesil Beach - connects the Isle of Portland to the mainland of the Dorset coast
Formation of a wave
1) The wind blows over the sea
2) This creates ripples
3) These ripples become bigger swells
4) Swells approach land
5) The sea becomes shallower
6) The bottom of the wave slows due to friction
7) The top keeps going and forms a crest
8) The crest topples forming a breaking wave
Two parts of a wave
- Swash: the movement of the wave up the beach
- Backwash: the movement of the wave back down the beach
Characteristics of a constructive wave
- Created by short fetch
- Small, gentle waves with low energy
- Deposit sediment
- Swash is stronger than the backwash.
Characteristics of a destructive wave
- Created by large fetch
- Big, strong waves with high energy
- Erode the coastline
- Backwash is stronger than the swash
Spring tide:
When the moon is between the Earth and sun their combined gravitational pull creates the biggest bulge of water and the highest tide
Neap tide:
When the Earth, moon and sun form a right angle their gravitational pull interferes with one another giving the lowest high tides and highest low tides - small tidal range.
Tidal range:
The tidal range determines the vertical range of erosion and deposition and the length of time the littoral zone is exposed to subaerial weathering
Tidal Bores
When water from an open stretch of ocean is confined in narrow sections of estuaries the tide is amplified
