Coasts Flashcards
explain sedimentary rocks
- they are clastic meaning they are made up of cemented sediment particles rather than interlocking crystals
- formed in stratas (layers) with joints which provides weaknesses and makes limestone permeable along with other jointed sediemntary rocks whereas other ones are porous due to the presence of air spaces
- rocks that are younger erode faster than the others as they are softer and weaker, older sediment is buried deeper and is subject to more intense compaction with strongersedimentation- making them more resistant
- forms scree at the base due to mass movement
- limestone erosion rates: 1-2cm/yr, chalk erosion rate: 1-100 cm/yr
- example: Old Harry, Purbeck, Dorset (chalk)
give examples of areas from the most resistant rock to the least resistant rock
most resistant: IGNEOUS- Land’s End, South Cornwall (granite)
resistant rock: METAMORPHIC- St Ives, Cornwall (slate)
resistant sedimentary rock: SEDIMENTARY- Blackers hole, south Purbeck, Dorset (Limestone)
least resistant rock: Holderness, NE Coast, (boulder clay)
explain the cave-arch-stack-stump sequence
- the headland protrudes out into the sea as it is more resistant which means wave energy is concentrated on it due to wave refraction
- wave action attacks weaknesses in the headland due to abrasion and hydraulic action leading to cavitation
- this widens cracks into crevices and into caves
- caves can be eroded to form blowholes as the ceiling collapses
- marine erosion deepens the caves until they connect up andan arch is created and erosion continues and the roofof the arch becomes unstable from the widening of the arch due to weathering and other sub-aerial processes
- the arch eventually collapses by blockfallto form a stack
- continual undercutting and HA in the joints at the base of the stack creating a stump like Old Harry’s wife
what are the 5 different types of mass movement?
landslide
slumping
mudflow
rockfall
soil creep
describe how the differential erosion of alternating and contrasting rocks affects the coastline?
This leads to a series of different landforms forming along the coastline and differing rates of recession. Higher rates of erosions will lead to the formation of bays whilst areas with more resistant rock will simply see faults and joints. It produces complex cliff profiles through the variety of different rock types. Headlands are likely to coincide with resistant rocks and will be characterised by relatively slow rates of recession.
explain the conflicts and winners + losers occurring in the sustainable management of blackwater estuary, essex
conflicts
- the west mersea fisherman were concerned that sediments could choke and kill oysters and water sea level changes could remove oyster habitats
- the RSPB were concerned about the increased erosion and flooding of their site opposite the farm which could change bird habitats
- conflicts have been resolved as research showed that the oysters and bird habitats actually improved as a result, farmers were compensated for land
winners:
- Environmental winners: Water quality in the estuary has improved because of expansion of reef beds that filter and clean the water, Important bird and oyster nurseries were enhanced
- Economic winners: Additional income streams from ecotourism and wildlife watching were enhanced
- Social winners: New paths and walkways were created for leisure activities
losers:
- local residents downdrift, reduces the volume of water travelling up the essex estuaries and creeks which could flood settlements
- led to the flooding of Abbot’s hall farm which led to socio-economic losers as farmers lost their agricultural land, however their land was bought for market value
explain the approach of managed realignment in Abbotts Hall farm, blackwater estuary, Essex
- they have adopted a ‘finding space for water’ philosophy which involves managed retreat
- coastal squeeze due to future sea level rise and storm surges make maintaining flood embankments unsustainable
- landowners and farmers have discussed giving up land to sea
- a CBA concluded that since the soil quality and land value were low, it was not worth maintaining the embankments
- it was the largest coastal realignment project in europe, costing £645,000, CHEAP
- the Essex Wildlife Trust purchased the Abbot’s Hall estate in Essex on Blackwater estuary and converted more than 84 hectares of farmland into salt marsh and greenland through 5 breaches in the embankments, farmers were compensated
- it is sustainable as the 49 ha of additional mudflats and saltmarshes absorb incoming higher seas and storm surges without any local damage
- new wetland bird habitats created, wading birds return for feeding and nesting
- CBA showed that sea wall was not cost-effective, soil quality poor
describe the essential features of the back shore
- It is a part of the beach above the high-tide mark and abutting the cliff base. It is only affected by exceptionally high tides and during severe storms. On the backshore we see a storm beach and pebbles.
- area between the high water margin and the landward limit of marine activity. Changes only happen here in storm events.
what is geological structure?
refers to how the rock is arranged on a macro-scale and looks at the arrangement of different rock types in relation to each other.It looks at the rock strata, deformation and presence of faulting.It looks at the rock strata, deformation and presence of faulting.
how can geological structure influence cliff profiles?
Geological structure largely influences cliff profiles in terms of the landforms that form as a result. If it is a discordant coastline then they are to see headlands and bays but if it is a concordant coastline they will see haffs and coves. Geological structure closely relates to the resistance of the rock and so it determines the rate of coastal recession in the different areas also.
what is rotational slumping?
common where softer rock overlies harder rock, it causes rotational scars, repeated slumping creates a terraced cliff profile
- A rotational scar is a fresh, curved, unweathered and unvegetated rock surface on the cliff face.
- The detached slope section, often with vegetation intact on top of the slump, forms a beach or terraced cliff profile.
- Slumping is facilitated by the presence of water, which adds weight (increasing the gravitational force) as well as lubricating it, reducing friction.
explain the two different cliff profiles
steep and unvegetated cliffs
- produced where marine erosion dominates
- there is little or no debris at the base as it is broken by attrition and transported offshore or along the coast
shallow and vegetated cliffs
- they have a convex profile (curved like the interor of a circle)
- there is debris at the base becuase sub-aerial processes slowly move sediment downslope, but marine erosion is unable to rmeove it from base
- produced where there is little active marine erosion
explain the beach profile
- storm beaches result from high-energy deposition of very coarse sediment during the most severe storms
- berms typically of shingle/graves, result from summer swell wave deposition
- the middle area of the beach is mainly sand, but the sand is coarser where berms/ridges have been deposited than in channels and runnels
- offshore ridges formed by destructive wave erosion and subsequent deposition of sand and shingle offshore.
explain the SMP in chittagong and why they are so vulnerable
a coastal climate resilient infrastructure project (2012) supported by the Asian Development Bank (ADB) aims to ‘climate-proof’ the area
- 1.5m rise in sea level would flood 22,000km sqaured and displace 15 million people
- 40% of farmland will be lost (salt water intrusion and directly)
- mangroves dissapearing, reducing protection from surges
- funnelling bay of bengal
this involves:
- improving road infrastructure for farmers and markets through raising embankments to 60cm above normal flood levels and making them resilient to CE
- creating new market areas with sheds raised on platforms above the expected 2050 sea level
- constructing, improving or extending 25 tropical cyclone shelters, taking account increase in cyclone magnitude
- training in climate resilience and adaptation measures
- it was loaned US$60 million by the IFAD and project was rated as satisfactory
how does lithology affect resistance? (explain 3 types)
1) mineral composition
- some rocks contain reactive minerals eaisly broken by chemical weathering, e.g. calcite in limestone
- other minerals are more inert that chemically weather more slowly
2) rock type
- sedimentary rocks are clastic (sediment particles compacted together) and these are often reactive and easily chemically weathered
- igneous rocks are crystalline with strong chemcial bonding
- rocky coasltines differ in resistance
3) structure
- rocks with fissures or air spaces erode more easily
what is it and explain the formation of a wave-cut platform
it is a flat rock surface exposed at low tide, extending out to sea from the base of a cliff
1) wave action at the base of the cliff between high and low tidemeans that hydraulic action and abrasion undercuts the clif to form a wave cut notch
2) this continues and the cliff above the notch is left unsupported and eventually collapses
3) the cliff retreats leaving a wave cut platform which is the base of the cliff that is left
4) this process maintains a steep cliff profile
what does porous, permeable and pervious mean?
permeability- the ability for water to be infiltrated into the rock
pervious- where there are joints and bedding planes leading to percolation, e.g. limestone
porous- small air pockets and holes in the rock allowing for the percolation of water, e.g. chalk
what does the morphology of discordant coasts lead to
the altering of the distribution of wave energy and rate of erosion through wave refraction
what are discordant coastlines?
- this is where the rock starts runs perpendicular to the coast forming headlands and bays - example: the isle of Purbeck’s eastern coast leading to headlands at peril point and durlston head, swanage bay has formed
explain the successful sustainable ICZM in Namibia as part of climate change policy
- long stretch of coastline of varying value
- it is called the skeketon coast due to Benguela current causing thousands of shipwrecks
- Namib desert runs all the way along the coast creating very inhospitable currents
Namibia’s national policy on climate change launched in 2013:
- emphasisd sustainable adaption measures to reduce vulnerability
- it aims to strengthen the governance of the coastline, improve QOL and maintain ecosystems
how is coastal management changing?
it is increasingly using the concept of littoral cells to manage extended areas of coastline. throughout the world, countries are developing schemes that are sustainable and use holistic ICZM strategies
- littoral cells are natural subdivisions of the coastlines containing sediment sources, transport paths and sinks.
there are 11 littoral cells in the Uk which are relatively closed systems, there are some transfers between however so managing large sections as a whole is more sensible
the second round of SMPs in 2004 changed many HTL strategies to MR and do nothing perhaps due to the fact that they were not aware of the rapid recession rates that were to happen due to climate change.
what is pore pressure?
it is the pressure that the water exerts on the rock when the pores are full
what were the different management strategies put into place in Namibia in the 3 different areas and what was the benefit and drawback of this SMP?
1) Skeleton coast in the Namib desert with isolated rural settlements and many wildlife areas
LOW COST MANAGEMENT OPTIONS
- prevent future development of coasal buffer zone experiencing recession
- conserve wetland habitats
- stabilise and protect sand dunes
- reduce poverty so people are able to prepare themselves (build better homes)
2) Small tourist settlements like Henties Bay
MODERATE COST OPTIONS
- beach nourishment
- protecting Kelp beds and restoring sand dunes
- rehabilitation of wetland ecosystems
- early warning systems for residents of high tides
3) Larger settlement important for industryand trade like Walvis bay
EXPENSIVE OPTIONS
- sea walls
- relocation of vulnerable communities
- raising of infrastrcture (ports and roads)
- building barrages and barriers
positive:
- they managed to effectively split resources to meet the needs of the population through building sea walls around industrial areas that could not move and using sustainable forms of protection
negative:
- however the limited protection in which this soft engineering offered meant that it led to the forced relocation of the rural settlements, displacement in community leading to fall in lived experience
what are destructive waves like?
- they degrade a beach
- high waveheight, low wavelength
- backwash > swash
- drags sediment back to sea
- scours beach
- 13-15 break/minute
- high energy
- causes cliff retreat
- plunging breaker
- steep beach
what is rockfall/blockfall?
- most likely to occur when strong, jointed and steep rock faces/cliffs are exposed to mechanical weathering or marine erosion,happens on slopes over 40 degres
- once broken away, it can form scree at the bottom of the cliff
blockfalls- similar to rock falls but here a large block of rock falls away from the cliff as a single piece.
what is mudflow?
Flows occur when unconsolidated fine grained sediment, e.g. silts and clays, mix with large volumes of water. They’re common in weak rocks such as clay or unconsolidated sands. They become saturated, lose their cohesion, and flow downslope.
- difference between a slide and a flow is that in a slide the material remains intact but in a flow the material becomes jumbled up
examine the influence of dips on cliff profiles
Landward dipping- they are relatively steep and stable, decreasing recession rates
Seaward dip- high angle produces low-angle profile with one rock layer facing the sea, low angle produces steep face with overhanging rocks
Horizontal dipping- vertical profiles with notches where weaker strata have been eroded, reflecting weathering and small scale mass movement
describe the essential features of the nearshore
- it isthe zone extending seaward from the low water line beyond the surf zone, it defines the area influenced by the nearshore or lowshore
- Shallow water close to the tide line but covered by water at normal low tides Here we see the formation of ridges and runnels.
explain folds
- they are bends in rocks formed by pressure during tectonic activity which makes rocks buckle and crumple - the main two types are anticlines and synclines - folden rock is often more heavily fissured and jolted, meaning they are more easily eroded, also increases erosion by increasing angle of dip and causing joins through the stretching along anticline crests an compressed in syncline troughs
explain the differential erosion on cliffs due to their complex profiles
- groundwater flows through the permeable sands but cannot through the impermeable clay. water flow along the sand/clay interface weakens the material leading to slumping
- poor water pressure (the internal force within cliffs exerted by groundwater) in the saturated layers pushes rock particles apart, reduces fractions and lubricates lines of weaknesses
- wave cut notches are created by erosion of the weak coal layers with more resistant siltstone overhanging the coal below
- the resistant rock creates a ‘bench’ feature at the cliff base
what might influence how vulnerable a cliff is to mass movement?
- lithology and structure of a cliff can determine mass movements it is vulnerable to
- weathering processes cancontribute to the loosening of cliff faces so that mass movements are more likely
- water from rainfall is often a key cause of mass movements
- angle of the slope will also affect vulnerability
what is a CBA and how is it difficult?
it is worked out by seeing if the benefits outweigh the costs and so a value of the land is a key consideration in the decision making process
- it is controversial as the value of property is dependant on how at risk it is as a home, at very high risk it could be worth norhing whereas a very similar house which is safe could be worth £300k
- some human costs (worry, stress) and environmental costs (value of biodiversity) are very hard to quantify in financial terms
what is landward dipping strata?
produces steep profiles on 70º-80º as downward gravitational force pulls loosened blocks into place, very stable with few rock falls
when it develops horizontal joints it will encourage weathering and mass movement
what is a terraced cliff profile?
this where the cliff profile is stepped due to lithology or fractures in the rock.
- it can often form after slumping
what is a wave-cut platform?
a curved indentation of about 1-2m high extending along the base of a cliff. it forms between the high and low tide marks, where destructive waves impact against the cliff.
explain faults
- formed when he stress of pressure not which a rock is subjected, exceeds its internal strength (causing it to fracture). the faults then slip along fault planes. - it significantly increases erosion since faulted rocks are much more easily jointed - huge forces are involved in faulting and displacing them and therefore either side of the fault line, rocks are often heavily fractured example: in bantry bay in cork in the republic of Ireland there is a major fault which runs SW-NE down the centre of the bays. the limestone is weakened allowing rapid fluvial erosion
how are waves created?
waves are created through friction between the wind and water surface, transferring energy from the wind into the water. this generates ripples, which grows into waves whedn the wind is sustained.
what is differential erosion
where cliffs are composed of differing lithology, leads to different sections of a cliff eroding/receding at different rates. it can also be produced when there are alternating permeable and non-permeable strata
they may form a ‘bench’ feature at the cliff base and further up overhanging sections until they collapse by mass movement.
however, the overall rate of recession is determined by the resistance of the weakest rock layer
explain joints
- (vertical cracks), these are fractures caused either by contraction as sediments dry out or by earth movements during uplift - they are fractures created without displacement and occur in most rocks, dividing rock strata up into blocks with a regular shape - jointing increases erosion rates by creating fissures which marine erosion processes such as HA can exploit example: in bantry bay, the limestone is heavily pointed, leading to more rapid fluvial and marine processes in adjacent sandstones
what are beach profiles like in winter?
destructive waves scour beach winter and create offshore bars and flatter beaches
- destructive waves occur at a higher frequency
- berms are eroded by plunging waves and high-energy swash
- strong backwash transports sediment offshore (offshore bars are made)
- destructive, high-energy waves dominate in the winter, lowering angle of beach profile and spreading shingle over the whole beach
