Coasts KQ1 Flashcards
What is a Coast?
- Boundary between land and sea
- Interaction between land, water, air and living things
Why are Coastal environments different?
1) Variations in human and natural processes
2) Differing coastal environments
3) Diverse landforms formed by coastal processes
Why are Coasts dynamic?
1) Constantly shaped over time due to:
- Coastal processes (E.T.D)
- Coastal Factors (W.T.C.G.E.H)
Factors affect coastal environments
1) Waves
2) Tides
3) Currents
4) Geology
5) Ecosystems
6) Human Activities
> Why Traffic Congestion Gets Extremely Heavy
Waves
1) Main shaping force of coastal environments
2) Winds blowing across oceans transferred to surface of water
3) Energy from winds transferred to water shapes coast when breaking on land
Tides
1) Daily alternate rise and fall in sea level
2) Due to gravitational pull of sun and moon
3) Changes every 6hrs, 2 high and 2 low tides/24hrs
4) Affect coastal erosion, transportation and deposition
5) During high tides, waves reach parts of coast not subjected to wave action during low tides.
- More erosion and sediment transportation away from coasts during high tide
Currents
1) Large scale continuous movements of water
2) Driven by prevailing winds blowing in one direction
3) Play important role sediment transportation and temperature regulation
4) Shape coasts through erosion, transportation and deposition
- Cool water away from poles > equator vice versa
- Milder climates in coastal environments
Geology
1) Arrangement and composition of rocks
2) Arranged in layers, alternating layers of hard and soft rocks
- concordant (=), discordant (ll)
3) Rock composition determines hardness and resistance to erosion
4) Different rocks give rise to different coastlines due to different rates of erosion
Ecosystems
1) Plants and animals that interact with each other and environment
2) Coral Reefs
3) Mangroves
Human Activities
1) Living trading fishing and engaging in recreational activities
2) Housing and Transportation
3) Fisheries and aquaculture
4) Recreation and tourism
Factors affecting wave energy
1) Wind speed
- Faster = greater energy
2) Wind duration
- Longer = larger waves = greater energy
3) Fetch
- Greater fetch = greater energy
Waves in open oceans
- Long wavelengths, low wave heights
Waves close to shore
1) Approaching coastline
- Base of wave interacts with seabed
- Depth reaches half their wavelength, wave shapes start to change
2) Near coastline
- Base of wave slows due to friction
- Wave height increases, wave length decreases (volume stays the same)
3) Nearest coastline
- Base of wave stops completely due to friction
- Wave crest becomes too steep and topples over
- Releases energy as it breaks on coast
4) Breaking on coastline
- Erodes rocks and transports them away
- Traps air as it crashes, releasing white water
Constructive waves
- Break far from shore
- Deposits finer material, forming gentle slopes
- Strong swash and weaker backwash
- Carries sediment onto shore, minimal sediment eroded
- Builds up coasts overtime, forms beaches
Frequency: 6-8/min
Prominent process: Deposition
Occurs @: Gentle + sheltered coastlines
Destructive waves
- Break violently on shore with high energy
- Finer material transported away
- Leaves coarser materials behind, forms steep coastlines
- Weaker swash (erodes coastline) and strong backwash (Transports sediments away)
- Coasts become more eroded and sediments deplete over time
Frequency: 10-14/min
Prominent process: Erosion
Occurs @: Steep + Open coastlines
Wave refraction
Def: Waves changing direction when approaching coastline
- Cause by friction between base of wave and seabed
1) Converging
- Bends towards headlands
- Energy more concentrated
- Erosion more prominent
2) Diverging
- Bends away at adjacent bays
- Energy dispersed, middle waves continue at same speed
- Erosive energy decreased, deposition more prominent
Coastal Processes
1) Erosion
2) Transportation
3) Deposition
Erosion
> S.A.H.A
1) Solution
- Seawater reacts chemically with soluble minerals, dissolving them (i.e. Carbonic acid and limestone)
- Rocks weaken and disintegrate
2) Attrition
- Sediments smash and rub against each other
- Rocks break down smoother and rounder
3) Hydraulic action
- Repeated pounding of waves against coasts form cracks
- Waves trap air in crack, exerting pressure within the cracks
- Repeated compression and decompressions weaken and shatter rock
4) Abrasion
- Waves hurl sediments against coast and scrapes the coast
- Sediments chisel, cut and breakdown the rocks
- Weakens surface and breaks down coast
- Able to undercut coasts
> Many different erosional processes occur at any one time, producing different landforms and coastal features, making coasts different
Sediment transportation: Longshore drift
1) Prevailing winds blow at oblique angle
2) Waves approach coast at same angle
3) Swash washes sediment up the coast at an angle
4) Backwash carries sediment perpendicularly down due to gravity
5) Zig-zag movement of sediment known as beach drift
6) Simultaneously, waves approaching coast generate
longshore currents parallel to the coast
7) Combined effect of beach drift and longshore currents are known as longshore currents, transporting sediments along the coast
> Transportation of a variety of sediments differ in degree along all coasts, resulting in differing coasts
Sediment deposition
- Occurs when waves lose energy and are no longer able to transport sediments.
- Depends on location of coast:
- Fine sediments: sheltered coasts w/ calm waters
- Coarse sediments: Open and exposed bays where higher wave energy carry away small sediments
- Large sediments usually deposited first, followed by smaller sediments
> Deposited sediments vary in type and size, resulting in differing coastlines
Factors affecting transportation
*Refer to Hjulstorm curve
1) Velocity of wave
- Higher V = Erosional/Transportation
- Lower V = Depositional
2) Sediment Load
- SL > Wave energy = Depositional
- SL < Wave energy = Transportation
3) Slope gradients
- Gentle = constructional waves = more deposition
- Steep = destructive waves = more erosion
Erosional Landforms
Def: Dramatic landforms including;
1) Cliffs and shore platforms
2) Headlands and bays
3) Caves, arches, stacks (and stumps)
Cliffs and shore platforms
Cliff: Steep, near vertical rockface found along coast
Shore platform: Flat area at bottom of sea cliff made up of coarse eroded materials
Formation:
1) Erosional processes erode a crack on the rock surface, enlarging crack to form notch
2) Notch deepens to produce a big hollow space called a cave
3) Further erosion causes roof of cave to collapse and form a steep cliff
4) Erosion continues, undercutting cliff and forming overhanging cliff
5) Overhanging cliff collapses due to gravity, sediments deposited at foot of cliff
6) Materials carried and transported away / hurled against cliff to further aid erosion
7) Cliff retreats inland and shore platform forms at base.
Headlands and bays
Headlands: Cliffed coasts that extend and protrude into sea
Bays: Wide inward curves of coastline where beach is formed
Formation:
1) Waves approach DISCORDANT coast. Less resistant rock erode faster than more resistant rocks
2) Less resistant rocks erode to form bays
3) Remaining, more resistant rocks remain and extend into sea, forming headlands
4) Wave refraction concentrates wave energy on headlands, eroding them. At bays, deposition occurs. Overtime, erosion and deposition may straighten the coastline
Caves, arches, stacks (and stumps)
Caves: Area hollowed out by wave action
Arches: Overhanging bridge of rock
Stacks: Pillar of rock left behind after arch has collapsed
Stump: Eroded remains of a sea stack
Formation:
1) Waves attack lines of weaknesses at bases of headlands, forming notches. Continuous wave actions enlarge the notches, forming caves that undercut the headland.
2) Caves may develop on 2 sides of a headland, eventually joining up / Cave may erode to other side of headland, leaving an arch behind
3) Repeated erosion and widening of cave causes roof of arch to collapse due to gravity, leaving behind a stack and shortened headland.
4) Stacks are attacked at base, undercut and collapse, leaving behind a stump
Depositional landforms
Def: Formed when sediments are deposited more quickly than they are eroded. Include;
1) Beaches
2) Spits and tombolos
Beaches
Def: Zone of sediment deposition
- Composition and size depends on origin of sediment
- Sediment size may change due to erosion
Formation:
1) In sheltered waters/bays, waves diverge due to wave refraction. Energy is dissipated when they reach coast
2) Sediments are deposited in the bay, forming bay-headed beach.
Factors affecting beach formation
1) Size and type of sediment
- Finer material = gentle slopes
- Coarse material = steep slopes
2) Origin of materials
- Determined by currents (Currents determined by weather)
Sediment sorting along beaches
Beaches: constructive coasts
> Constructive waves = strong swash, weaker backwashes
- Fine sediments found nearer waters edge & Coarser materials found inland due to decreasing wave energy
- Large sediments deposited furthest away from coastlines because waves have not enough backwash energy to carry them back down
Spits and tombolos
Spits: Long narrow ridge of sediments w/ one end attached to land and other projecting out into sea
Tombolo: Spit that connects 2 islands together, exposed during low tides
Formation:
1) Materials transported parallel to coast by longshore drift
2) Lateral movement continues until coast reaches abrupt curve. Change in coast does not stop sediment transportation. Sediments continue to deposit onto seabed according to direction of original longshore drift.
3) Sediments accumulate and rise above sea level, forming spit
4) Due to occasional change in wind direction and wave refraction, ends of spit curve, forming recurved/hooked spit.
5) Spits stabilized by vegetation
6) Spits may extend and connect to offshore island, forming tombolo
7) 2 spits may meet to form tombolo
