Flashcards in Coasts Deck (41):
Describe the essential features of the backshore
- the part of the beach closest to the coastline
- dry under normal conditions
- berms (horizontal plateau formed from deposition) without vegetation
- only exposed to waves during storms
Describe the essential features of the nearshore
- where waves steepen and break and surge out to foreshore
- sediment is transported in this zone
Suggest three different criteria that might be use din classifying coasts
- sea level rise/fall
What are subaerial processes
- land based processes which later the shape of the coastline
- weathering (e.g. Freeze thaw, chemical weathering)
- mass movement (e.g. Landslides, slumping)
Describe the essential features of the coastal plain
- flat low lying land adjacent to the sea
- cliff/wave cut notch
- gets flooded during storms
What is the difference between a concordant coast and a discordant coast
- concordant when the arrangement of the rocks are parallel to the coastline
- discordant when arrangement is perpendicular to coastline
Name and example of a concordant and discordant coast
- concordant eastern coast of Adriatic Sea
- discordant south west Ireland
Explain what a haff coastline is
- a lowland coast where the long bars and lagoons are parallel to the shore
Headlands and bays are a feature of discordant coasts, explain why marine processes gradually smooth out such coasts
- resistant rocks form headlands meaning the shape of the coastline causes waves to refract as they approach headlands
- concentrates energy on headlands, increasing rate of erosion
- allowing coast to flatten out.
Examine the influence of dip on cliff profiles
- the dip of a rock layer is the angle of tilt from the horizontal.
- if a rock layer dips towards sea the blocks of rock may slide under the influence of gravity (mass movement)
- if the angle of the dip is landward, weathering and erosion may attack exposed bedding planes and joints, creating an irregular profile
What are the micro features of a cliff and how are they formed
- cliff profiles may include many protrusions and indentations due to erosion, as well as miro features such as caves, blowholes and geos
Characteristics of igneous rocks
- cooled magma (granite and basalt)
- more resistant to marine erosion and weathering than sedimentary rock.
Features of metamorphic rocks
- gneiss, marble
- formed from igneous and sedimentary rocks that were subjected to intense heat and pressure
- most resistant rock
Features of sedimentary rocks
- formed underneath oceans (limestone, sandstone)
- least resistant rocks
Describe how the differential erosion of alternating and contrasting rocks affects the coastline
- sedimentary rocks are permeable whereas metamorphic rocks are impermeable.
- the presence of water in these rocks can affect weathering and mass movement e.g. Slumping due to saturation
- some rocks such as limestone contain soluble minerals and so are vulnerable to chemical weathering such as carbonation (sea water absorbs co2 which splashes onto limestone and dissolves it)
Explain why vegetation is a a factor affecting coastal recession
- stabilises soft sediment low energy coastlines based on sand and mud.
- plant succession over time pioneer plants colonising bare areas as they change the conditions of soil by adding humus (decayed vegetation), retaining moisture and stabilising loose ground.
- sand dunes, where xerophyte plants such as marram grass grow, and salt marshes where halophyte plants such as glasswort grow provide buffer zones between and and sea. Sand dunes take the impact of storms and salt marshes absorb coastal flooding.
Explain why estuaries are ideal for the development of salt marshes
- estuaries are low energy environments where tidal conditions bring seawater and sediments in and out and rivers bring fine MUDs and silts and deposit them at the estuary
- the clay particles sick to one another (flocculation) and once deposited are colonised by algae.
- salt marshes can then be found at the edges of estuaries.
Explain the formation of embryo dunes
- sand dunes form where there is a plentiful supply of sand and a large area for it to dry out.
- onshore winds blow sand towards land and obstacles such as vegetation and shingle ridges which trap the sand
- embryo dunes are formed first.
Explain the formation of dune slacks
- at high tide or under storm conditions, seawater may reach the dips in the sand dunes, called dune slacks.
- this allows other plants such as march orchids to grow.
Apart form colour what distinguishes yellow dunes from grey dunes
- yellow dunes tend to be the highest, and may form a ridge near the dune front with marram grass.
- grey dunes are known as the mature dunes because their humus (decayed vegetation) content is greater. The clima vegetation is either pine forest (high acidity) or oak forest (slightly neutral).
Why is marram grass so important to the formation of sand dunes
- able to colonise the stable dunes and help hold the sand together and trap more sand.
What is the difference between tides and currents
- tides are driven by the gravitational force of the moon, water moving up and down the beach over a period of time
- current is the motion of the water, caused by density difference in water masses, cohesive streams that flow through the water
Describe what happens to waves when they reach shallow water
- forward movement starts to occur when the depth is less than the wavelength
- the base of the wave is slowed down by friction against the sea floor while the top of the wave rushes ahead
- the wave crest topples over and breaks onto the shore.
Distinguish between constructive waves and destructive waves
- constructive, larger swash than backwash, build up the beach
- destructive strong backwash weak swash, remove sediment
What is the difference between hydraulic action and corrosion
- abrasion, destructive waves pick up particles of sand and pebbles and scrape or throw them against a cliff as they break, this scratches the rock wearing it away, results in undercutting a cliff at high tide level.
- attrition occurs when boulders are continually moved around by waves especially in the breaker zone, as the sediment moves they collide with each other, rocks are broken down into smaller pieces.
Describe the suite of coastal landforms most commonly found in areas of sedimentary rock with defined bedding planes and joints.
- wave cut platform, where a cliff is eroded at its base, leaving the tour rock unsupported which eventually collapses, leading to coastal recession
- cliffs, vertical slopes caused by waves undercutting land at high tide or constantly if there is no beach, as the cliffs undercut gravity causes mass movement in the unsupported rocks.
- caves, arches, stacks and stumps
Headlands in the sea cause waves to be refracted and all wave energy to be focused on the sides of the headland, hydraulic action and abrasion will at first form caves which often meet from opposite sides to form a tunnel above which is a rock arch
- eventually the top collapses leaving a pillar of rock called a stack, the stack continues to be eroded cutting notches all around leaving it unstable causing it to collapse leaving the base which is called a stump.
Name and describe the 4 sediment transportation processes
- suspension, small particles carried in the water e.g. Silts and clay, currents pick up large amounts during a storm.
- solution, minerals are dissolved in sea water and carried in solution, load comes from cliffs made form chalk/limestone.
- saltation, load is bounced along the sea bed e.g. Small pieces of shingle or large sand grains
- traction, pebbles and large sediment are rolled along the sea bed
What is longshore drift
the movement of material along a coast by waves which approach at an angle to the shore but recede directly away from it.
Describe how a tombolo is formed
tombolo is formed after longshore drift carries sediments cross a gap between the mainland and an island forming a narrow low ridge of sand and pebbles
- it may be a spit at first but when deposition links the island no mainland together it is a tombolo
- the isle of Portland in Dorset is joined to the mainland by a tombolo
Explain how a recurred spit is formed
- longshore drift moves sediment along the coast over a long period of time, when the sediments reach a gap in the coastline they are carried for a short while in the same direction until they are deposited on the seabed.
- over time this material is deposited causing it to real through the surface of the sea to form a narrow strip of land across the bay or estuary.
Describe how cuspate foreland is formed
cuspate foreland is a low lying headland, formed when significant longshore drift is from opposite directions along the coast, sediment is deposited across a bay from both directions forming two spits
- the two spits converge and shelter the area behind in the bay, salt marshes form and enough deposition will form low lying land.
Examine the factors affecting the stability of depositional features
vegetation- more stable - binds sediment together
Groynes- de-stabalise spits
What are sediment or littoral cells
Coasts divided into areas called littoral cells. Each cell contains a cycle of sedimentation including sources, transport paths, and sinks.
Describe the three types of weathering
Mechanical- weathering breaks down rocks due to physical force
chemical - weathering involves a chemical reaction
biological- weathering often is sped up through the action of plants,animals,bacteria
Give examples of mechanical weathering
Threeze thaw - constant expansion and shrinking as temp changes causes cracking
Salt crystallisation - Growth of salt crystals in cracks can exert a breaking force
Give examples of chemical weathering
carbonation- the slow dissolution of limestone due to rainfall
hydrolysis - breakdown of minerals to form new clay minerals
Give examples of Biological weathering
plant roots - trees and plant roots growing in cracks and fissures forcing rocks apart
rock boring - many species of clams bore into rock and secrete chemicals that dissolve rocks
What is mass movement
movement of material such as soil, rock mud or snow down a slope under the influence of gravity
Describe three different types of mass movement
rockfall - rapid freefall of rock from steep face due to the action of gravity
Mud flow - occurs on steep slopes under 10 degrees. Rapid and sudden movement which occurs after periods of heavy rain
Landslips- occasional rapid movements of earth or rock
Describe the effects of mass movement on the coastal landscape
causes cliffs to retreat in size and beaches to be destroyed