Coasts Flashcards
what is a system?
many interrelated components that work together to carry out some source of process
what is an open system?
a system in which both matter and energy are able to transfer across the system boundery
what are the inputs of a system
matter and energy transferring into a system across the system boundery
what are the outputs of a system?
matter and energy transferring out of a system across the system boundery
what are the components of a system?
the parts that make up a system
what are the stores of a system?
where matter accumulates and is stored for a length of time
what are the flows/transfers of a system
a connection between stores, along which matter flows
what is dynamic equilibrium?
the balanced state of a system when it’s inputs and outputs are equal
what is feedback?
when an element of a system changes due to outside influence
what is positive feedback?
when the process tends to increase the change in the system
what is negative feedback?
when the process seems to counter the change and maintain equilibrium
what is the backshore?
the area between the high water mark and the landward limit of marine activity.
changes normally take place here only during storm activity
what is the foreshore?
the area between the high water mark and the low water mark
the most important zone for marine processes in times that are not influenced by storm activity
what is the inshore?
the area between the low water mark and the point at which waves cease to have any influence on the land beneath them
what is the offshore?
the area beyond the point at which waves cease to have any impact on the land beneath them
any activity is limited to the deposition of sediments
what is the swash zone?
the zone on the landward side of the surf zone where waves wash up the shore
what is the surf zone?
the zone of a beach past the swash zone, where the waves break
what is erosion?
the wearing away of the earth’s surface by the mechanical action of processes of glaciers, rivers, marine waves and wind
what is weathering?
the gradual breakdown of material over time in situ
what is mass movement?
the gradual downhill movement of material under the influence of gravity
what is fetch?
thr distance a wave has traveled across the sea
what is physical weathering?
the break-up of material without any chemical changes taking place
what is chemical weathering?
the break up of material due to the influence of chemical reactions where salts may be dissolved or a clay-like deposit may result which is then easily eroded
what is biological weathering?
the breakdown of material by organic activity
describe wetting and drying as a process of weathering
-rock undergoes constant wetting and drying
-rock expands when wet and contracts when dry
-constant expanding and contracting causes cracks to form
describe exfoliation as a form of weathering
-rock expands when hot and contracts when cold
-constant expanding and contracting causes cracks to form in the rock
explain the roots of plants as a process of weathering
-plant roots on cliff tops can expand tiny fissures
-sub-surface seaweed can also attach to rocks and weaken them during movement
explain oxidation as a process of weathering
-rocks containing iron compound experience oxidation when exposed to oxygen and water from the air and sea
-this causes disintegration
describe crystallisation as a process of weathering
the high salt content of sea water can lead to the growth of salt crystals within the rock that exert pressure on joints and lead to fracturing
explain carbonation as a process of weathering
coastlines comprised of chalk or limestone are dissolved by acidic rain and seawater
explain freeze-thaw as a process of weathering
-water fills cracks in the rocks
-this water then freezes when temperatures drop and expands
-this expansion exerts pressure within the rock, expanding cracks
explain surface animals as a process of weathering
-surface animals such as puffins may excavate nesting burrows in cliffs
-sub-surface creatures such as limpets may also remove rock when they attach to it
what are subareal processes?
processes that take place on the cliff face above the high water mark
the combined efforts of weathering and mass movement
what is a rockfall?
a form of mass movement
the sudden collapse or breaking away of individual rock fragments at a cliff face
most commonly associated with steep or vertical cliffs in heavily jointed and often resistant rock
triggered by mechanical weathering or an earthquake
forms scree at the bottom of the slope, a temporary store of material (forms an input when eroded away by marine processes)
what is a landslide (mass movement)
a block of rock moving rapidly downhill along a curved slide plane (often a bedding plane parallel to the ground surface)
remains largely as one block of material
triggered by earthquakes or heavy rain when the slip surface becomes lubricated (friction reduced)
very rapid, posing threat to people and property
what is runoff (mass movement)
when overland flow occurs down a slope or cliff face, small particles are moved downslope, potentially forming an input to the sediment cell
transfer of both water and sediment
toxic chemicals can contaminate storm water and pose threat to coastal ecosystems
what are mudflows (mass movement)
earth and mud flowing downslope after heavy rainfall (usually over unconsolidated bedrock such as clay)
water gets trapped in the rock, increasing pore water pressure (important form of energy and factor in slope instability) which forces rock particles apart and leads to slope failure
sudden and fast flowing, considered a natural hazard
what is slumping (mass movement)
differs from a mudslide in that it’s slope surface is curved rather than flat
commonly occur in unconsolidated clays and sands, often when permeable rock overlies impermeable rock, causing a build up of pore water pressure
also known as landslips
characterised by a sharp break of slope and formation of a scar, multiple landslips can result in a ‘staircase’ appearance on the cliff face
what is soil creep (mass movement)
extremely slow movement of soil particles downhill
when the soil gets wet or freezes it expands, pushing soil particles upwards, as it dries or thaws, these particles sink vertically (down the slope) due to gravity
this zigzag movement is similar to longshore drift
cannot be seen in action but can be implied by the formation of shallow terraces, the buildup of soil on the upslope sides of walls, leaning telegraph poles/trees and bending of tree stumps
what factors affect the rate of erosion?
-rock type/ geology
-wave energy
-seasons
-subareal processes
-coastal management
what is coastal morphology
the underlying geology (rock type) and lithology (geological structure) of a coast
what are strata?
layers of rock (in a cliff)
what are bedding planes?
horizontal, natural breaks in the strata, caused by gaps in time during periods of rock formation
what are joints?
vertical fractures caused by either contraction as sediments dry out, or by earth movements during uplift
what are folds?
formed by pressure during tectonic activity, which makes rocks buckle and crumple
what are faults?
fractures formed when the stress or pressure to which a rock is subjected exceeds its internal strength
the faults then slip or move along fault planes
what is a dip?
refers to the angle at which rock strata lie (horizontal, vertical, dipping towards the land/sea)
what is relief?
the height and slope of the land
what is a concordant coastline?
a coastline with alternate bands of hard and soft rock that lie in parallel to the coast
what is a discordant coastline?
a coastline with alternate bands of hard and soft rock that lie perpendicular to the coast
how are bays and headlands formed on concordant coastlines?
-the sea takes a long time to erode through a band of harder rock, finding weak points such as faults, joints and bedding planes to attack
-the sea eventually erodes through these weak points to the softer rock behind
-the softer rock erodes much faster than the harder rock
-the resulting landforms are an oval bay, created through the erosion of the softer rock, and two harder headlands at the mouth of the bay that face eachother.
eg, Lulworth cove
how do bays and headlands form on discordant coastlines?
-the bands of harder rock are more resistant to erosion than the bands of softer rock
-the bands of softer rock are eroded faster, forming bays, and the bands of harder rock erode slower, being left behind as headlands
-as the headlands become more pronounced they suffer from wave refraction, and erosion makes the coastline straight again for a time
-wave refraction cannot occur when the coastline is straight and the process begins once more
-over time the coastline retreats further and further inland
explain the formation of a cave
-cracks at the base of the headland within the inter-tidal zone become exposed through hydraulic action, which pressurises air and causes the cracks to widen
-cracks are further widened by weathering processes such as salt crystallisation and wet and dry weathering that affects chalk
-over time, the cracks widen and develop as wave-cut notches
-further processes of abrasion and hydraulic action will deepen the notch, forming a cave
explain the formation of an arch
-as a result of wave refraction, which distorts the wave direction, destructive waves concentrate their energy on the sides of a cave, deepening it
-wave refraction affects all three sides of a headland, if two caves are aligned the waves may cut through, forming an arch
explain the formation of a stack
-wave cut notches widen the base of an arch due to wave refraction
-vertical joints are exposed to the tall breaks associated with destructive waves. joints can also be weathered from above through carbonation in limestone (this forms blowholes)
-over time the arch becomes unstable and collapses under its own weight, forming a stack
explain the formation of a stump
-a stack is eroded at its base creating new wave-cut notches
-subareal processes continue to weaken the stack from above
-the stack eventually collapses to form a stump
explain the formation of a wave-cut notch
-when waves break at the foot of a cliff, erosion tends to be concentrated close to the high-tide line.
-this creates a wave-cut notch
explain the formation of a wave-cut platform
-as a wave-cut notch gets bigger due to hydraulic action and abrasion, the cliff is undercut and the rock above it becomes unstable
-this overhanging rock eventually collapses, forming a wave-cut platform
why protect the coast?
to protect:
-homes
-businesses
-the environment
what does the coast need to be protected from?
-coastal flooding
-coastal erosion
why protect the coast statistics
-half the world’s population live within 60km of the coast
-3 quarters of all large cities are at the coast
what is hard engineering?
artificial, man-made structures designed to interfere with natural processes
what are groynes?
timber or rock structures built perpendicular to the coast that trap sediment, disrupting littoral drift
what are the advantages of groynes?
-work with natural processes to build up the beach
-increases tourist potential and protects the land behind I
-not too expensive
what are the disadvantages of groynes?
-terminal groyne syndrome
-unnatural and unattractive
how much do groynes cost?
£5,000 - £10,000 each (at 200m intervals)
what are sea walls?
stone or concrete walls at the foot of a cliff, or at the top of a beach
they usually have a curved face to reflect wave energy back out to sea
what are the advantages of sea walls?
-effective at preventing erosion
-often have a promenade for people to walk along
what are the disadvantages of sea walls?
-reflect wave energy rather than absorb it
-intrusive and unnatural looking
-very expensive to build and maintain
how much do sea walls cost?
£6,000 per metre
what is rock armour/ rip rap
large rocks placed at the foot of a cliff or at the top of a beach, forming a permeable barrier to the sea
absorb wave energy
break up waves, but allow water to pass through
what are the advantages of rock armour/ rip rap
-relatively cheap to construct and maintain
-often used for recreation (fishing/ sunbathing)
what are the disadvantages or rock armour/ rip rap
-intrusive and unattractive
-rocks do not match local geology
-can be dangerous for people climbing over them
how much does rock armour/ rip rap cost?
£1,000 - £3,000 per metre
what are revetments?
sloping wooden or concrete structures at the base of a cliff or top of a beach that break up the wave energy
often used at the base of sea walls
what are the advantages of revetments?
-relatively inexpensive to build
what are the disadvantages of revetments?
-intrusive and unnatural
-need high levels of maintainance
how much do revetments cost?
up to £4,500 per metre
what is an offshore breakwater?
a partially submerged rock barrier, designed to break up the waves before they reach the coast
what are the advantages of offshore breakwaters?
-effective permeable barrier
what are the disadvantages of offshore breakwaters?
-visually unappealing
-potential navigation hazard
how much do offshore breakwaters cost?
similar to rock armour -
£1,000 - £3,000 per metre
(depending on materials used)
what is soft engineering?
a ‘softer’ more environmentally friendly approach to costal defences
often uses natural materials and tries to work with, not against, natural processes
what is beach nourishment?
the addition of sand or pebbles to an existing beach to make it higher or wider
the sediment is usually dredged from the nearby seabed
what are the advantages of beach nourishment?
