Coastal Systems and Processes (workbook 2)
Marine Processes- caused by waves from the sea wearing down the cliff foot
Sub-aerial Processes- caused by action of weather on cliff face
Movement of particles
Transport: The carrying of eroded particles from one location to another
Detachment : The separation of particles from the parent material
Entrainment: The picking up of eroded particles to enable transportation
Deposition: Occurs when sediment load exceeds the ability of water or wind that it is carrying
Erosion= wearing away and removal of material
CAVITATION - Collapse of bubbles that have formed within moving water and release energy against rocks
ATTRITION- Erosion of material being transported by the sea, making it smaller and rounder through collisions
ABRASION/CORRASION- Grinding away of rocks and cliffs as smaller particles are thrown at the cliff. This can cause undercutting
WAVE QUARRYING- Air is forced into cracks and has an explosive effect which loosens material which is then transported and removed
WAVE POUNDING- Repeated force pf the waves breaking against a cliff to weaken rock
HYDRAULIC ACTION- Breaking waves can force air into gaps into rock, exerting pressure and dislodging rock
CORROSION- Dissolving of rock and sediment by chemicals. This is more effective in warmer water
Mass Movement
Factors that affect the rate include:
Rock Type
Direction of Dip
Bedding of Rock
ROCKFALL- rapid movement that occurs on the steepest slopes when the whole slabs of rock suddenly detatch
LANDSLIDE- occurs along a flat or planar slide plane. particularly when the underlying bed is impermeable leading to high moisture content
ROTATIONAL SLIP- slide plane is a concave shape and when saturates the rock will collapse under gravity
MUDFLOW- when soil or clay becomes saturated or flows rapidly downhill
SOLIFLUCTION- slow downhill movement of saturated soil
SOIL CREEP- particles rise and fall downhill which is a very slow process
Weathering= Breakdown of rock in-situ due to atmospheric weather
Agents of erosion= wave and wind
Mechanical weathering- granular disintegration
Chemical weathering- change in the chemical composition of the rocks
FREEZE-THAW- water enters the areas of weakness and freezes. Ice occupies more space than water and exerts pressure, Fragments of rock break off producing scree/talus
HEATING & COOLING- rocks are heated to extreme temperatures during the day and cooled at night which causes stress on the rocks and disintegrates it (insolation)
WETTING & DRYING- rocks expand when wet and contract when dry which causes them to crumble. This is also known as slaking and is common in intertidal areas
EXFOLIATION- rocks heat and cool at different rates due to conductivity and the outer layers split off. Common in areas where rainfall is high and temperatures are low
PRESSURE RELEASE- removal of overlying rocks or ice causes the rock to relax and the outer layer of the rock splits to form domes. This is known as sheeting
CRYSTAL GROWTH- growing crystals resulting from evaporation of saline water prises the rock apart. Common in semi-arid areas
ORGANIC GROWTH- roots exert a destructive force and prise rock apart. Burrowing animals may remove soil and expose the rock
CARBONATION- carbon dioxide reacts with water to produce weak carbonic acid which reacts with limestone to produce soluble calcium bicarbonate
HYDRATION- rocks absorb water and well making it easier to break down
OXIDATION- oxygen combines with minerals. If iron is in the rock it will form rust which collapses the molecular structure
HYDROLYSIS- carbonic acid releases hydrogen in water which reacts to cause disintegration. This affects rocks containing feldspars
CHELATION- lichens and mosses produce weak acid which dissolves rock. Significant in the formation of soil
SOLUTION- certain minerals e.g halite dissolves in water
Coastal zones
onshore zone- towns/ports
backshore zone- only affected by waves in storm conditions, includes cliffs, beaches and sanddunes
swash zone- moves up as swash and down as backwash
intertidal/nearshore zone- waves are modified and sediment moves
surf zones- broken waves travel towards the shore
breaker zone- varies in width depending on type of wave
offshore/subtidal zone- water depths are greater than half the wavelength of incoming waves. Limited sediment, where tidal currents are most effective
factors that affect amount of energy:
prevailing wind
fetch
water depth
SOLUTION- removal of dissolved minerals and weathered products by rainfall and percolating groundwater. Carried in water (dissolved)
SUSPENSION- small material carried in the flow of water
SALTATION- particles are lifted upwards and forwards before going back to their original surface (bounce)
TRACTION- pebbles and larger sediment are rolled along the sea bed
High Energy waves- cause erosion and transportation to form cliffs and shore platforms
Low Energy waves- create deposition and coral reefs
Tides (gravitational pull from the moon)
Wind- creates sand dunes
High Waves- powerful waves are steep, have short wavelengths and are tall. They have more energy as there is more water
Fetch- the distance a wave has been blown. The larger the fetch, the more powerful the wave
Dominant wave- the fastest wave
Prevailing wind- The most common wind direction. In Britain it is the south west. Same direction as dominant wave
Dominant wind- strongest wind but prevailing wind is most common
Formation of a wave
1) prevailing wind. friction transfers the energy to create waves
2) movement of water in deep water is in a circular orbit
3) wave starts to orbit in an elliptical shape
4) shallow water creates friction so the crest moves faster than the base
5) wave height increases and wave length reduces
6) wave height = wave length
7) swash moves waver up the beach. water from a previous wave creates backwash
constructive wave- low wave height, low frequency, strong swash, weak backwash, wave period of 6-8 per minute, build up the beach
destructive wave- high wave height, high frequency, steep shape, weak swash, strong backwash, wave period of 10-14 per minute, remove sediment from beach
wave refraction- bending of waves in the foreshore zone until they break parallel to the shore. It depends on the depth of the water offshore
swash-aligned beach- waves approach the beach parallel to the land, backwash becomes powerful creating rip currents
drift-aligned beach- waves approach the beach at an oblique angle (30 degrees) and creates longshore drift
waves change direction as they approach the shoreline due to a change in the depth of water. They go slower in shallower water and faster in deeper water so the wave bends. This concentrates the energy around the headland and makes them more vulnerable to erosion. At bays accretion will occur which will slow the wave down even further causing more refraction
deposits coarser material to form beaches at high tide or mudflats at low tide. Britain receives 2 high tides a day with a gap of 12 hours and 25 minutes due to the orbit
NEAP TIDE- where the tide reaches it's lowest level. The sun and the moon are at right angles to each other
SPRING TIDE- where the tide reaches it's highest level. The sun and moon are in allignment
MACROTIDAL- range of more than 4m
MESOTIDAL- range of between 2 and 4m
MICROTIDAL- range of up to 2m
Case studies- Canadas Bay of Fundy and Western-Super-Mare in Somerset
Case studies- Mediterranean, Majorca, Helsinki in Finland
Small tidal range= concentrated erosion on a small part of the cliff and creates deposition of narrow beaches
INTERTIDAL ZONE- area where rock and sediment will be exposed for several hours each day between high tides allowing sub-aerial processes to operate
Outline the role of tides in shaping coastal landscapes
High tide or spring tide creates more erosion to form caves, arches and stack
Low tide or neap tide creates more deposition to form salt marshes and mudflats
Currents
Tidal currents- surface current on a local scale. affected by gravitational pull of the moon and the sun. the movement of water on a daily basis
Surface ocean currents- longshore currents. determined by wind direction. they are caused by friction of air dragging water molecules
Thermohaline circulation- upwelling affected by temperature as warm air rises and cool falls. it is affected by the salinity as salty water sinks as it is more dense
Rip currents- strong surface current flowing seawards away from the shore (backwash). they have the power to erode and scour beach material
Rock Types
Igneous rocks- formed deep within the earth and have volcanic origin as they formed from magma. They are crystalline as they are made of interlocking crystals so they are resistant to weathering and erosion e.g granite and Basalt
Cold water moves towards the equator from the poles in the form of global ocean currents. Warm water moves away from the equator towards the poles
Sedimentary rock- formed from deposited sediments that have become consolidated over many years.
Sandstone is made from quartz which is fairly hard.
Limestone is made from CaCo3 which has numerous horizontal and vertical joints.
Chalk is made from skeletons of marine plankton
Metamorphic rock- used to be either igneous or sedimentary rock but have been changed as a result of intense heat and pressure. They are crystalline e.g marble and slate
PERMEABILITY- a substance that allows water to flow through it
POROSITY- amount of area between particles of a rock
PERVIOUSNESS- rocks that have joints or fissures where water can flow e.g limestone
IMPERMEABLE- a rock that doesn't absorb water or allow water to pass through it e.g granite
Factors affecting
High temperature- chemical weathering e.g hydrolysis, evaporation. Biological weathering occurs. less mass movement
Low temperature- physical weathering and carbonation
High precipitation- strong physical and chemical weathering e.g freeze- thaw and carbonation. causes mass movement e.g slumping
low precipitation- slight physical
High wind speed- high marine erosion e.g HA, WP, high aeolian erosion, stronger waves, more mass movement
Low wind speed- less processes, more deposition, gentle waves
Isle of Purbeck
Has complicated geology
Concordant south coast
Discordant east coast
creates differential erosion
EAST COAST- chalk, Wealden sands & clay, Purbeck limestone
SOUTH COAST- Purbeck limestone
low energy coast as winds are greater so deposition is dominant
Landforms = Swanage bay, Stutland Bay, Ballard Point, Durlston Head
high energy coast as has strong prevailing winds and a large fetch
Lulworth Cove
horse-shoe shaped bay
KEY:
grey =portland stone
orange =purbeck beds
yellow= wealden beds
green= greensand
cream= chalk
aspect- the direction the coastline faces. Linked to fetch and prevailing wind
micro-climates- localized climates
Sediment
clastic sediment- comes from the weathering and erosion of rocks
biogenic sediment- shells and skeletons of marine organisms
fluvial sediment- transported to the coastline environment by rivers
non-cohesive sediments- sand and larger particles that are transported grain by grain
cohesive sediment- small mud and clay particles that cling together due to electromagnetic bonding
HJUSTRUM CURVE- describes the movement of sediment in a river or at a coast
LONGSHORE DRIFT- the waves approach the coast at an oblique angle
water no longer has the energy to continue the transportation of sediment. Sand, shingle and pebbles can be deposited in high energy environments and form beaches but silt and clay need to be deposited in lower energy environments
Landforms are in dynamic equilibrium where over time adjustments balance themselves out
Sediment cell
The transportation of sediment by longshore drift in the nearshore zone in a relatively self-contained area.
There are 11 across the coast of England and Wales
It is a closed system
Movement within one cell should not affect beaches in an adjacent cell
Has inputs, outputs, processes and stores
Starts and finishes at headlands and bays e.g Flamborough Head to The Wash
SEDIMENT BUDGET- total amount of sediment circulating within a cell
Paris Climate Summit
global warming
President Trump withdrew from the agreement
2015
200 countries in agreement
Raise in temperature of no more than 2 degrees in this century
Cherbourg Penninsula & Chesil Beach
Input at Chesil Beach = sand which causes deposition which forms a tombolo
River Estuary at Southampton water transports fluvial sediment to the Isle of Wight
Headland at Cherbourg Penninsula creates wave refraction which causes concentrated erosion
Sediment is being stored in the offshore zone
Holderness
Sediment cell number 2
retreating at an average of 2mm per year
Threat of flooding and erosion
Hard strategies being used
Southampton Water
Rivers
Test
Itchen
Hamble
Inputs
Intertidal erosion
Subtidal erosion
Cliff erosion
River load
Saltmarsh
Marine import
Outputs
Intertidal siltation
Subtidal siltation
Dredging
Saltmarshes
Inputs and outputs balanced
Angle of Dip
Angle at which rock layers have been set down
SEAWARD SLIDE PLANE- rocks dip towards the sea= more vulnerable to mass movement. not resistant so land falls towards foot
LANDWARD SLIDE PLANE- rocks dip towards the land= more secure. mass movement is less likely to occur