Coasts Flashcards
What is a high energy coastline?
Give a UK example
Stretches of the Atlantic-facing coast, where the waves are powerful for much of the year
Where the rate of erosion exceeds the rate of deposition.
Rocky coasts and erosional landforms tend to be found here.
UK - Cornwall or north-western Scotland.
What are low energy coastlines?
Give a UK example
Stretches of the coast where the waves are less powerful or where the coast is sheltered from large waves
Where the rate of deposition exceeds the rate of erosion.
Sandy and estuarine coasts and landforms such as beaches, spits and coastal plains tend to be found here.
UK - Lincolshire and Northumberland.
What type of coastline does Cornwall have?
Resistant rock coastline.
It is rocky and can withstand the frequent winter storms without suffering from rapid erosion.
What type of rocks does the Cornwall coastline consist of?
Igneous rocks - e.g. basalt & granite
Older compacted sedimentary rocks - e.g. old red sandstone
Metamorphic rocks - e.g. slates and schists
What is a coastal plain landscape?
Give a UK example
Areas of weaker and younger sedimentary rocks - e.g. chalks, clays, sand & sandstone.
UK - The Wash (the largest estuary system in the UK)
What are the inputs of the coastal system?
Marine - waves, tides & storm surges
Atmospheric - weather/climate, climate change & solar energy
Land - rock type and structure & tectonic activity
People - human activity & coastal management
What are the processes of the coastal system?
Weathering, mass movement, erosion, transport & deposition
What are the outputs of the coastal system?
Erosional landforms, depositional landforms & different types of coasts.
What is the littoral zone?
It stretches out into the sea and onto the shore.
Tides and storms affect a band around the coast.
It is constantly changing because of the dynamic interaction between the processes operating in the seas, oceans and on land.
Why does the littoral zone vary?
Short-term factors - e.g. individual waves, daily tides & seasonal storms
Long-term factors - e.g. changes to sea levels or climate change
What occurs in the backshore and foreshore?
The greatest human activity.
The physical processes of erosion, deposition, transport and mass movement.
What processes effect sediment supply ?
How?
Weathering & erosion - produce output in the form of sediment.
Transportation and deposition - produce coastal landforms.
What categories are used to classify coasts?
Geology, level of energy, balance between erosion and deposition & changes in sea level.
What is the Lulworth Crumple?
Thin beds of Purbeck limestone and shale are clearly visible in the side of the cliff.
These layers of rock are folded in response to tectonic movements about 30 million years ago.
What is coastal morphology?
The shape and form of coastal landscapes and their features.
What is lithology?
The physical characteristics of particular rocks.
Define strata
Layers of rock.
Define bedding planes
Horizontal cracks.
Natural breaks in the strata, caused by gaps in time during periods of rock formation.
Define joints
Vertical cracks.
These are fractures, caused either by contraction as sediments dry out or by earth movements during uplift.
Define folds
Give an example
Formed by pressure during tectonic activity which makes rocks buckle and crumple.
e.g. Lulworth Crumple
Define faults
Formed when the stress or pressure to which a rock is subjected, exceeds its internal strength (causing it to fracture).
The faults then slip or move along fault planes.
Define dip
The angle at which rock strata lie (horizontally, vertically, dipping towards the sea or dipping inland).
Define relief
Height and slope of land.
What are the characteristics of igneous rocks?
Give an example
Crystalline, resistant & impermeable.
e.g. granite
What are the characteristics of (joined) sedimentary rocks?
Give an example
S - formed in strata
e.g. limestone, chalk, sandstone & shale
JS - permeable
e.g. sandstone & limestone
What are the characteristics of metamorphic rocks?
Give an example
Very hard, impermeable and resistant.
e.g. marble & schist
What is a concordant coast?
Give an example
Where bands of more resistant and less resistant rock runs parallel to the coast.
e.g. Isle of Purbeck
Describe the rock type on Dorset’s coast
Varies between resistant Purbeck limestone (which forms steep cliffs) to less resistant clays and sands.
Alternate along the coast, so that where a resistant rock is eventually eroded - allowing the sea to break through to less resistant rock behind - erosion follows more quickly.
What are Dalmatian coasts?
Concordant coastline.
They have formed due to sea level rise.
Valleys and ridges run parallel to each other.
Where the valleys flooded, the tops of the ridges remained above the surface of the sea - as a series of offshore islands that run parallel to the coast.
What are Haff coasts?
Concordant features - long spits of sand and lagoons - aligned parallel to the coast.
Define discordant coast
Where the geology alternates between bands of more resistant and less resistant rock, which run at right angles to the coast.
How do headlands affect incoming waves?
They force incoming waves to refract or bend - concentrating their energy at the headlands.
This increases their erosive power leading to a steepening of the cliffs and their eventual erosion into arches and stacks.
How do bays affect incoming waves?
Their energy is dissipated and reduced.
This leads to the deposition of sediment - forming a beach.
What happens the water as a wave approaches the coast?
It becomes shallower and the circular orbit of the water particles changes to an elliptical shape.
True or False
Wavelength and velocity increase as the wave approaches the coast.
False
True or False
Wave height increases as it approaches the coast.
True
What causes a wave to break?
Force pushes the wave higher so that it become steeper before spilling.
Describe the characteristics of constructive waves
Low, surging waves - with a long wavelength.
Strong swash, weak backwash.
Beach gain.
Describe the characteristics of destructive waves
High, plunging waves - with a short wavelength.
Weak swash, strong backwash.
Beach loss.
Why does beach morphology change?
Beaches consist of loose material, so their morphology alters as waves change.
Why does beach profile change?
Seasonal changes in wave type create summer and winter profiles.
Explain summer beach profiles
Constructive waves are more common and they are less frequent so wave energy dissipates and deposits over a wide area.
The swash deposits larger material at the top of the beach - creating a berm.
The backwash becomes weaker - it only has enough energy to move smaller material so the beach material becomes smaller towards the shoreline.
Explain winter beach profiles
Destructive waves occur at a high frequency.
Berms are eroded by plunging waves and high energy swash.
Strong backwash transports sediment offshore.
The backwash exerts a current known as a rip or undertow - dragging sediment back as the next waves arrives over the top.
What are swell waves?
Originate in mid-ocean and maintain their energy for thousands of miles.
UK coast - they appear as larger generated waves.
What is fetch?
The distance of open water over which waves move.
True or False
The greater the fetch, the larger the wave
True
What are the 2 main types of waves?
Constructive & destructive
What is abrasion?
When waves advance, they pick up sand and pebbles from the seabed.
when they break at the base of the cliff, the transported material is hurled at the cliff foot - chipping away at the rock.
What is hydraulic action?
When a wave advances, air can be trapped and compressed.
When the wave retreats, the compressed air expands again.
Weakens joints and cracks in the cliff - causing pieces of rock to break off.
What is corrosion?
When cliffs are formed from alkaline rock or cement bonds the rock particles together, solution by weak acids n seawater can dissolve them.
What is attrition?
The gradual wearing down or rock particles by impact and abrasion, as the pieces of rock are moved by waves, tides and currents.
Reduces the particle size and makes stones rounder and smoother.
How does lithology influence erosion?
Any geological weaknesses are eroded more quickly.
Bands of more resistant rock between weaker joints and cracks erode more slowly .
What is differential erosion?
Selective erosion of areas of weakness - as opposed to more resistant areas and types of rock.
What are stacks and stumps?
Isolated pillars of rock that lie just off the coast and are surrounded by water.
Stumps - completely covered at high tide.
What are shoreline platforms?
Flat rocky platforms that extend out from the coast.
How are wave cut notches created?
When waves break against the foot of the cliff, erosion tends to be concentrated close to the high-tide line.
Creates a wave-cut notch, which begins to undercut the cliff.
How are shoreline platforms created?
As the wave-cut notch gets bigger, the rock above it becomes unstable and eventually the upper part of the cliff collapses.
As these erosional processes are repeated, the notch
migrates inland and the cliff retreats .
Where are the steepest cliffs found?
Where rock strata are vertical and horizontal or have almost vertical joints.
Where are the gentlest cliffs found?
Where rock dips towards or away from the sea.
How are caves formed?
Erosion exploits weaknesses in the cliff. When joints and faults are eroded by hydraulic action and abrasion, this can then create caves.
When are blowholes formed?
If the overlying rock collapses, a blowhole will develop as the cave opens up at ground level. During storm high tides, seawater can be blown out of these blowholes with considerable and spectacular force.
How are arches formed?
If two caves on either side of a headland join up, or a single cave is eroded through a headland, an arch is formed.
How are stacks formed?
The top of the arch will become unstable and collapse – leaving an isolated pillar of rock, called a stack.
How are stumps formed?
The stack itself continues to be eroded by the sea. As it collapses and is eroded further, it may only appear above the surface at low tide, and is now known as a stump.
Explain the process of longshore drift
As the waves advance, material is carried up the beach at an angle. The backwash then pulls material down the beach at right angles to the shore.
What is traction?
Relatively large and heavy rocks are rolled along the seabed.
What is saltation?
Smaller and lighter rocks ‘bounce’ along the seabed.
What is suspension?
Lighter sediment carried by the water.
What is solution?
Dissolved sediment carried in the water.
What are tides?
Changes in the water level of seas and oceans – caused by
the gravitational pull of the moon and, to a lesser extent, the sun.
UK coastline experiences 2 high and low tides a day.
What are spits?
Along narrow feature, made of sand or shingle, which extends from the land into the sea.
How are spits formed?
Sand or shingle is moved along the coast by longshore drift, but if the coastline suddenly changes direction, sediment
will begin to build up across the estuary mouth and a spit will start to form.
What are offshore bars?
Submerged ridges of sand or coarse sediment.
How are offshore bars formed?
Created by waves offshore from the coast.
Destructive waves erode sand from the beach with their strong backwash and deposit it offshore in bars.
What are barrier beaches?
Where a beach or spit extends across a bay to join two headlands.
What are barrier islands?
Where a beach becomes separated from the mainland.
What are tombolos?
A beach (or ridge of sand and shingle) that has formed
between a small island and the mainland.
How are tombolos formed?
Deposition occurs where waves lose their energy and the tombolo begins to build up.
What are cuspate forelands?
A triangular-shaped headland that extends out from the main coastline.
How are cuspate forelands formed?
It occurs where a coast is exposed to longshore drift from opposite directions. Sediment is deposited at the point where the two meet, which forms a natural triangular shape as it builds up.
What are pioneer species?
The first plants that colonise bare ground.
They begin the process of plant succession.
They modify the environment by binding sand or soil
with their roots and adding nutrients when they die and decay.
What is the purpose of creeping plants?
They help the sand or mud in dunes and salt marshes to retain moisture. They also modify the environment by providing shade as well as improving the soil.
What is the climatic climax community?
The final community adjusted to the climatic conditions of the area.
What are embryo dunes?
Embryo dunes are the first dunes to
develop. They grow into bigger fore dunes – which are initially yellow in colour, but darken to grey as decaying plants add humus.
Where to salt marshes develop?
In sheltered areas where deposition occurs.
Where salt and fresh water meet.
Where there are no strong tides or currents to prevent sediment deposition and accumulation.
What happens within sediment cells?
The sediment moves between the beach, cliffs and sea through the processes of erosion, transport and deposition. Any action taken in one place has an impact elsewhere in the cell.
Each cell operates between physical barriers that prevent the sediment from moving any further along the coast.
What are halophytes?
Salt-tolerant species - such as glasswort and
cordgrass - that help to slow down tidal flow and trap more mud and silt.
What is the sediment budget?
The amount of sediment available within a sediment
cell.
What is positive feedback?
If the sediment budget falls, waves continue to transport sediment (and erosion may therefore increase in some areas, because the sea has surplus energy).
What is negative feedback?
However if the sediment budget increases, more deposition is likely. The sea corrects itself, because it can only carry so much – and any surplus is deposited.
