Coasts Flashcards
Littoral zone
- Ocean, beach and area of land behind it
- Offshore, nearshore, foreshore, backshore
- Area of shoreline where land is subject to wave action
Primary and secondary coasts (coastal types)
- Dominated by land processes e.g. deposition from rivers
- Dominated by marin erosion/deposition
Rocky coasts and coastal plains (coastal types)
- Cliffs, creates erosional coasts + varying geodiversity
- Gradually sloping land, deposited sediment
Constructive and destructive waves
- Low height, long wavelength, strong swash (uninterrupted + starts at nearshore) = sediment berm
- High height, short wavelength, strong backwash
Different wave types in the short term (daily)
Plunging waves become swell waves
Wave types in the long term
- Seasonally: constructive common in the summer, destructive in winter
- Annually: reduced river sediment (dams), coastal management, climate change as storms means winter beach profile
Formation of headlands and bays
- Heavy rainfall creates rivers, causing v shaped valleys in bays, as it erodes at the soft rock
- Headlands erode as waves are concentrated on it (refraction). Headlands’ sediment then fills the bays, flattening out the coastline - headlands eroded, bays filled in
- Rising sea level meets back of the bay, eroding it, so coastline is still elongated
- All of this happens at the same time, but sea level rise disrupts/overrides the balance, so more erosion than deposition
Discordant coasts
- All rock types face the coast (perpendicular to ocean)
- Alternating rock type between hard and soft rock
What are concordant coasts
- Strata run parallel to coastline so waves interact with one rock type
- Geology might fold into anticlines and synclines
Dalmatian coast
- Tectonics compress layers into anticlines and synclines (plates are made up of multiple types of rocks, so don’t move in the same way, causing deformation)
- Sub-aerial weathering on anticlines as cracks are made when it’s folded
- Rivers/glaciers erode synclines
- Sea water floods synclines, causing parallel anticline ridges (islands) on the coast
Haff coasts
- Long sediment ridges topped by sand dunes
- Runs parallel to coast offshore
- Results in series of lagoons (haffs) between ridges and shore
Types of sea level change
- Isostatic: local and usually due to rebound from ice/glaciers melting
- Eustatic: global, SL affected by tectonics as subduction thrusts the seabed
Emergent coastlines
Away from marine processes and now terrestrial instead
Raised beaches
- Above high tide
- Reflects stages of uplift due to tectonics
- Smaller particles removed, pebbles/boulders remain
Fossil cliffs
- Nearly vertical cliffs, but inland
- Can find old sea caves and wave cut platforms
What are the LT eustatic sea level changes?
- Tectonics, where crust faulting/folding causes seabed displacement
- Post glacial, SL rose approximately 100m since last glacial maximum
- Sea level now slowly rising (CC and thermal expansion)
Submergent coastlines
- Fjords: submerged U shaped valley that’s overdeepened inland, rock lip at seaward entrance
- Ria: drowned valley due to river erosion
- Dalmatian: tectonically formed, submerged valleys
Ice formation/melting causing SL change (eustatic)
- During glacial periods
- Ice sheets form on high latitude land with evaporated water locked up as ice, so less water in the sea
Thermal changes cause SL change (eustatic)
- Global temps cause thermal expansion
- Water particles move faster/take up more space, increasing volume of ocean water
Post glacial adjustment causes isostatic SL change
- Rebound after ice sheet melts, land surface lifts out of the sea, SL appears to fall
How does subsidence cause isostatic SL change?
Land compressed (by weight of sediment, buildings, glaciers) and SL appears to rise
How does accretion cause isostatic SL change?
- Ice melts leading to sediment being deposited in large river deltas
- Causes increased weight (crustal sag) and delta subsidence
- SL appears to rise
Resistant geology
- Ancient rock more resistant due to millions of years of being compressed and compacted
- Permeability = water exploiting joints, creating more pressure, reducing stability
Bedrock lithology
- Different rocks side by side causes a variety of landforms
- Igneous: cooled magma
- Metamorphic: previous rock subjected to heat + pressure
- Sedimentary: compacted sediment + minerals cemented together (permeable)
How does unconsolidated material affect rates of recession
- Much easier to erode
- Lack of strength and easily exploited by water
Types of geological structures
- Layers become twisted/distorted
- Jointing: rock fractures
- Dipping: seaward or landward tilt exposing all or only the newest layers due to tectonics or SL rise, affects types of landforms we get
- Faulting: a fracture that causes relative rock displacement
- Folding: anticlines and synclines
Influence of structure on erosion rates
- Seaward dipping makes coast vulnerable to ocean erosion and landslides
- Fissures can be exploited, leaving microfeatures (more squeezing = more joints and fissures)
History of coast formation
- The first layer / oldest sediments were deposited at the bottom of the ocean (Sandstones / mudstones / limestone)
- The second layer include coal, from when this coast was around the Equator (continental drift)
- Sea level rose to cover this – lots of microorganism settled on the ocean floor to build layers of chalk
- Sea level fell – leaving rivers to erode away the chalk
- Basaltic lava spread on top, particularly into the river valleys
- Basalt was weathered / rock breakdown – leaving laterite soil behind, and eventually (sedimentary) laterite rock.
- A second layer of basaltic lava flows over the top, cools into hexagonal columns)
- That basalt layer gets weathered / breaks down – more laterite soil and more laterite rock
- A third layer of basaltic lava flows over the top
- Ice age: glaciers eroded away the very surface of that basalt
- Tectonics distorts the layers into anticlines and synclines
- The glacier eroded material (till) is deposited in the synclines
Alternating strata
One layer’s permeability/resistance affects other layers
What are permeability and resistance?
- Permeability depends on how jointed it is
- Resistance is how compact/compressed it is (depends on age)
Complex cliff profiles
Sloping, columns, overhanging + mass movement (which influences recession)
Which erosional processes create distinctive coastal landforms?
Mainly hydraulic action and abrasion, it exploits weak points
Wave cut notches
Rock at sea level of a cliff is eroded into a curved notch
Wave cut platforms
- Result from notches as unsupported cliff collapses and retreats
- Erosion and weathering can create rock pools or ridges
Cave, arch, stack, stump sequence
- Initially was a headland but was eroded
- Stump indicates where original coastline was
How does differential erosion influence recession rate
- Basalt undercut by marine erosion causing wave cut notch and platform
- Rate of erosion and debris varies over time
- Debris/material absorb wave energy on the platform, then break down and used for attrition until it disappears
- Basalt marine erosion means recession until waves can’t reach cliff base = equilibrium until SL rise
Differential weathering affecting rate of recession
- Sub-aerial weathering at backshore of bays, lower marine energy from refraction so cliff degradation from above
- Water from rain permeates laterite, not basalt, becomes saturated and heavier, stress>strength
3 types of mechanical weathering
- Crystallisation: saltwater evaporates, salt crystals form in joints, exert pressure, rock forced apart
- Freeze thaw: water freezes in joints and expands by 9%
- Shattering: daily temperature change means rocks expand and contract
Chemical weathering
- Seaweed acid: cells break, sulphuric acid dissolves rock as its minerals aren’t bonded
- Oxidation of iron minerals
- Carbonation of limestone
- Hydrolysis forms new clay minerals
Biological weathering
Boring molluscs - live on rocks, bore holes to get food which are now weak points for weathering to act
Hydraulic action
Force of waves compresses air in cracks and opens them to allow more air in, wave retreats and pressure is released so rock shatters
Attrition
Rocks hitting each other and break into smaller, rounder rocks = more surface area for abrasion
Abrasion
Force of bits of rock carried by destructive waves thrown against cliffs
What is corrosion?
- Chemical reaction between seawater and rock’s minerals then carried away by backwash
- Carbonates are more vulnerable
- Easily gets to small particles and don’t need cracks to exploit
Mass movement
- Downslope movement of material under the force of gravity
- Topple: influenced by geological structure, strata have steep seaward dip, undercutting = instability, then material topples
What is blockfall?
Hydraulic action or mechanical weathering dislodges blocks of rock and undercutting can lead to large falls
Rotational slumping
Curved failure surface and huge masses of material slowly rotate downslope
What are landslides?
Discrete blocks of rock sliding down a flat/linear slip plane (often the bedding plane)
Translational landslides
- Mudflow: common in weak rock (clay and unconsolidated sands), heavy rainfall and high tides = saturation, material loses cohesion, slides downslope
- Block slide: very low angle seaward dip in strata prevents fall but material still slides down towards the sea
What distinctive landforms are made by mass movement?
- Mudflows create rills (a shallow channel) and lobes (front edge of deposition)
- Block slides leave clean scars along the bedding plane
Rotational scars
- Bare scar faces between terraces
- Curved, unweathered rock with no vegetation
What are talus scree slopes?
- Accumulation of debris from angular rockfall (~40°)
- Larger boulders at core (talus), smaller on top (scree)
What is a talus slope?
- Series of rotational slumps, combination of different bits of many taluses
- Vegetation grows on top and meshes the different parts together, stabilising it after long time
- Percentage of vegetation shows whether cliff profile is active
- When material has been there for a while, ocean scrapes away oxidised rock that has changed colour, revealing original rock colour, showing breakdown
Terraced cliff profiles
Multiple detached slope sections with vegetation intact
How is coastal recession caused by physical factors? (Guinea)
- Geological: sand extraction for housing, so not transported to coastline
- Marine: rising SL of 10cm since 1950, 3m high swell waves during stormy monsoon months, strong waves on soft cliff
Coastal recession influenced by human actions (Guinea)
- Mangrove deforestation and diamond mining
- Dredging: removing material for ports, deep water so energy retained (more erosion)
- Coastal management: no beach nourishment, very expensive sea walls, interruption of sediment transfer
Why aren’t recession rates constant
- Depends on amount of contact time between sea and rock
- Tied in with equilibrium
Tides - daily tidal bulge
- Bulge = as the Earth rotates on its axis, water is dragged gravitationally towards the moon
- Inertia = bulge on opposite side as water hasn’t kept up
- Other sides are normal (balanced gravity + inertia), so low tide = two parts high, two low
- Where the bulges are will change over time
Tides - alignment
- Highest tide is spring high tide when sun and moon are aligned (every 2 weeks)
- Gravitational pull at its strongest
- Storm at same time has high impact
- Neap tide = sun and moon at a right angle means there are less low and high tides as gravitational pull is at its weakest
- An anticyclone at the same time means there’s barely any erosion
Tides - interaction
- Moon rotation is elliptical
- Perigean spring tides is when the moon and sun align, and the moon is at its closest to earth (4 times a year)
LT factors of recession rates
- Wind direction/fetch: largest waves from prevailing wind direction, distance that waves travel uninterrupted (gain energy)
- Seasons: storm events more likely in winter
- Weather systems: depressions are low pressure, intense + faster wind speeds, large destructive waves. Anticyclones are high pressure, calmer conditions and smaller waves
- Storms: very LP depressions and produce large, high energy destructive waves
Economic losses due to recession (Trinidad and Tobago)
- Dependent on petrochemical industry on east coast, so threatened by erosion
- All natural gas pipelines to Guayaguayare (most erosion there)
- Mayaro beach homes valued at over £700k
- Up to £5 mil to repair 300m of major road
- 400,000+ tourists last year for beach and eco tourism industry
Social losses due to recession (T&T)
- Loss of local coconut plantations and watermelon/veg cash crops
- Road damage from flood affects transport/access
- More erosion lowers value of coastal properties
- Relocation and community break up
- Social tensions with individual management
Types of sediment transportation
- Traction, saltation, suspension, solution
- Angle of wave attack determines direction
Longshore drift
- 30° swash
- 90° backwash
- Prevailing wind often determines direction
Sediment cell concept
- Stretch of coastline where material movement is mainly self contained
- Closed: natural barriers stop movement in/out
- Semi closed: small material can leave
- Open: wind, tide, currents remove material
Sources, transfers and sinks
- Sediment from cliffs, headlands, rivers and lagoons through erosional processes
- Sediment transported by longshore drift, currents, wind
- Deposited by gravity settling (drops to bottom of ocean) or flocculation (clay particles attracted to each other and clump)
Negative and positive feedback
- Effects of change stop it and erosion, cliff collapse and debris protect from erosion
- Effects of change encourage it, storms erode dunes and remove vegetation, can be further eroded
Dynamic equilibrium
- Despite balance, still constant movement and change
- Inputs balanced by outputs
Bayhead beaches
- Swash aligned
- Waves break at 90° + move sediment into bay = beach
- Refraction so erosion at headlands and bay is area of deposition
Recurved and double spit
- End of spit curved landward into shallower water (bay or inlet), more pronounced by different direction waves
- Two spits formed in different directions w lagoon behind and tidal gap to prevent them meeting
Offshore bars
- Ridge of sand offshore that can be submerged during high tide
- Formed by riptide currents after destructive waves
Barrier beaches/bars
- Sand/shingle beach connects two areas of land w a lagoon behind
- Spit grows and closes off bay
Tombolos
- Sand/shingle bar connecting coastline and offshore island or rock outcrop
- Formed by refraction around island, creating area of calm water and deposition (longshore drift can play a role)
T Test Standard Deviation
- Calculate average of all samples
- Sum of (Sample subtract sample average)^2
- Divide by (number of samples - 1)
- Square root the answer
T Test
- Outcome: ignore +/- and then compare with critical value (0.05)
- If calculated value is higher than critical value, accept hypothesis and reject null hypothesis (it is significant)
Halophyte and xerophyte vegetation
H - Plants adapted to growing in saline conditions and are salt tolerant
X - Plants that need very little water e.g. dunes where drainage means sandy soil doesn’t retain much water
Vegetation stabilisation
Holds sandy coastline together with roots and encourages deposition (reduce wind speed)
Dune successional development
- Embryo dunes
- Fore dunes: inland, sand accumulates and salt tolerant vegetation
- Yellow dunes: first main ridge, 30/40 yrs old, well established vegetation
- Grey dunes: more organic matter, has soil
- Heath dunes: deciduous woodland, moist soil w more nutrients
- First 3 are mobile dunes that can be disturbed/destroyed
Salt marsh successional development
Algae on bare mud, glasswort to stabilise, carpet of vegetation, height increase, climax
Local factors that increase flood risk
- Height: near or at SL, reclaimed land can exist below SL w sea walls
- Subsidence: when ground sinks/collapses, naturally happens through recently deposited sediment being compacted
- Vegetation removal: stability reduced, mangroves reduce wave height by 40%, reduces storm surge height by 0.5m
Storm surge flooding short term impacts
- Intense rainfall contributes to flooding
- Lower atmospheric pressure = SL rise
Climate change increases coastal flood risk
- Warmer oceans and additional heat energy
- Lower air pressure, faster winds, high doming of seawater and larger storm waves
- Kiribati: sea surface temp changes and bleached coral reefs cause stress in coral polyps and then expelled algae, so loss of protection
Climate change increase frequency/magnitude of storms and SL rise (Bangladesh)
- Storm surges but not tropical storms, more winds+waves and subsequent coastal erosion
- 55cm rise by 2011
How is the magnitude of threat of climate increasing flooding uncertain?
- Poor global data on average wind speed + wave height and poor forecasting
- Human related drivers: land use change, coastal development and pollution
- More people in lowland coasts
Mitigation and adaptation for CC causing flood risk
- solar panels and local food sources
- sea walls, rainwater harvesting and buy new land
Coastal flooding/storm surge events have economic and social consequences (Netherlands)
- 70% of GDP at risk from flooding, €7 billion water management cost and incremental €2 billion yearly
- Risk but tech allows econ to thrive and survive
- 66% of population live in flood prone areas
Flooding and storm surges have consequences for coastal communities in developed countries (Netherlands)
- To what extent do they have the capacity to absorb new technology- changes mindset to solving problems
- Engineering system holds back water at end of Rhine Delta that people live on
Climate change creates environmental refugees
- SLR ruins env resources necessary for subsistence lifestyles
- Saltwater contaminates and waste accumulates
- Coastal erosion destroys housing and arable land
Environmental refugees in coastal areas
- NZ refused residency status to Kiribati residents, just there for labour (accepted exceptional humanitarian grounds)
- Move country due to risks of climate change, want to be safe
Hard engineering in Portballintrae
- Failed to stop problem, instead reinforced it
- Groynes since 1904 but centre of bay continued to retreat, Leslie’s pier got in the way with refraction around it
- Sand nourishment/barrier at cliff base but beach continued to fall
- Protects 5,000 residents and 15,000 tourists (main income)
Economic costs of hard engineering in Portballintrae
£1.5 million preliminary investigation and £30 mil proposed cost
Beachfront closed for 2 years, temp beach hut closure and temp restricted car park access
Hard engineering alters physical processes and systems
Disrupts geography
Sand beaches now boulder orientated
Waves attack centre of bay
Leslie’s pier diffracts waves, creating low energy zone in shadow
Soft engineering
Works with natural systems to reduce coastal erosion + flood threat and helps to protect vital natural ecosystem services
Beach nourishment
- Artificially replenish sediment lost through erosion and longshore drift
- Enlarges it to attract tourists and dissipate wave energy at backshore
What is cliff regrading and drainage?
- Lower angle of rest for stability and supported at base with hard engineering
- Vegetation to trap/stabilise unconsolidated sediment, drainage reduces porewater pressures and mass movement risk
Dune stabilisation
Low impact + cost using old trees w fencing, replanting marram grass, reducing trampling, educating with info boards and boardwalks
Sustainable management
- Managing the wider coastal zone
- People and their livelihood + wellbeing
- Minimising environmental impact
Sustainable management meant to cope with future threats of increased storm events and rising SL (French Polynesia)
- Rare but devastating tropical cyclones
- Increased erosion + flooding
- SL rise will inundate the island
- Uncertainty about time and scale of SL rise
Sustainable management causes local conflicts in many countries (French Polynesia)
- Solutions might be opposite of what people want, creating social justice issues
- France as an ex ruler, NZ doesn’t want env refugees and China is a trade partner
Mitigation and adaptation needed for future stability (French Polynesia)
- Tackle cause of issues, NGO improve sustainability so more fish + food security + different attitudes
- Reduce and deal w effects of what has already happened, env refugees’ lives have been affected e.g. land degradation so they leave
How to evaluate coastal management
- Does it consider how the Environment will change over different timescales?
- Has all Legislation been accounted for?
- Is this based on our best Scientific knowledge?
- Have All stakeholders been consulted?
Coastal management uses littoral (sediment) cells to manage extended coastlines
- LT, all stakeholders, natural processes considered
- Managed as a unit w sources, flows and sinks
- Geopolitical situation across Mediterranean makes collaboration complex e.g. cultural differences + migration from Syrian crisis
Countries are developing sustainable schemes and using holistic ICZM strategies
- Local projects involve ecological alteration, so ICZM changes lifestyle to environmentalism?
- Very top-down approach so doesn’t look at poorest communities
- Bottom-up needs + objections are obvious to locals
- Becomes complicated w too many factors + stakeholders
- Mainly govmt decisions
No active intervention, strategic realignment, hold the line, advance the line (in order)
- coast allowed to erode and flood
- allows natural movement but directs it to certain areas
- coastal defence
- seaward defence and land reclamation
Cost Benefit Analysis and Environmental Impact Assessment
- CBA: Helps to decide if defending a coastline is economically justifiable
- EIA: Identify ST impacts of construction on the env, LT impacts of building new defences or changing policies
Perceived winners and losers
- Remain financially stable, communities + services remain in place, wildlife habitats are conserved
- Lose property, relocate and community splits up, destruction/disruption of habitats
Scale of challenge must be matched by scale of response
Policy decisions cause conflict in Chittagong
- No compensation for property loss
- Increased stress on coastline w rapid development/urbanisation
- Management can’t keep up w fast tourist development (haphazard + less holistic)
- Funding depends on grants and loans, fewer resources = less resistant structures
- Faster erosion w tropical cyclone frequency, dams remove sediment supply, removal of mangroves reduce stability
