2.3 - Coasts Flashcards
What is the size/type of waves controlled by?
-wind velocity (speed)
-wind duration (time)
-fetch (product of the first 2)
What is the fetch?
-area of contact between the wind and the water, and is where wind-generated waves begin
(friction upon surface causes ripples then waves)
-waves keep growing until limited by wind duration or fetch restriction
Describe destructive waves:
-from strong winds (common during winter)
-weak swash, strong backwash
-causes erosion
-shorter wavelength + higher frequency, larger amplitude
Describe constructive waves:
-from weak/no winds (common during summer)
-strong swash, weak backwash
-causes deposition
-longer wavelength + lower frequency, smaller amplitude
Name and describe the points of weaknesses (POWs) on a coastline:
-bedding planes (gaps between rock layers)
-joints (vertical cracks)
-fault line (a very big joint)
How is a wave-cut platform formed?
-waves undercut the foot of a cliff (attacking the POWs by the 4 erosional processes), forming a wave-cut notch
-notch gets larger, unsupported cliff above collapses causing the cliff to retreat over time (cliff increases in height too)
-the gently sloping expanse of rock at the foot of the cliff is the WCP (only exposed at low tide)
Describe the formation of a cave/arch/stack/stump:
-wave-cut notch develops at cliff base (by erosional processes at POWs)
-continued erosion causes the sea cave to form (large notch)
-cave eroded through, forms arch
-arch widens at base, roof collapses forming stack
-stack is eroded at base (forming another WCN), collapses, forming a stump
Describe the 2 types of coastline:
-discordant, rock types are perpendicular to shore
(can form headlands + bays)
-concordant, rock types are parallel to shore
(can form coves)
Formation of headlands/bays/beaches:
-discordant coastline eroded (at POWs by erosional processes), softer rocks eroded quicker and form bays
-bays sheltered from D-waves and have material deposited by longshore drift + C-waves to form beaches
-headlands protrude as the rock type is harder and is more vulnerable to further erosion
What is differential erosion?
erosion that occurs at varying rates due to the differences in resistance/hardness of the rock
Describe longshore drift and the motion it causes:
the ZIGZAG movement of material along a coast by constructive waves which approach at an angle to the shore (in the direction of the P-wind) but recede at 90 from it
-always draw arrows for P wind and direction of sediment movement
Explain how a spit/bar/tombolo forms:
-LSD transports sediment down a coastline, until a change in direction of coastline
-LSD continues to deposit material in a straight line away from coastline, until storm winds create a hook at the end
-bar crosses a section of water, encloses it (lagoon)
-tombolo forms a bridge to an island
Make sure to fully explain LSD and backwash/swash
Name 5 characteristics of a spit:
-salt marsh
-hook
-low in height
-attached at one end (although can be bar/tombolo)
-made of sand/shingle (+sand dunes)
(SHLAM)
What do groynes do for a coastal town?
-stop erosion and longshore drift to maintain the beach size
-maintains tourism for the beach
-visual pollution
-the larger beach will protect coastal houses
How do coastal sand dunes form?
-sand blown by wind further up beach and initially deposits it around an obstacle (rock/plant) and it accumulates, forms an embryo dune
-grows, forms a yellow dune, inhabited by marram grass
-grey dune forms due to increased amount of hummus (soil) from plants in dune
-mature dunes form, can support less specialised plants
What types of coral reefs are there? Describe them and give an example for each:
-fringing (close to land and extends out long distances, Tahiti)
-barrier (well defined coral zone separated from land by a shallow sandy bed lagoon, GBR)
-atoll (ring-like formation of reefs with lagoon in the middle, Palmerston)
What are the conditions required for coral reefs to form?
-warm water (20-28°C)
-shallow (15-25m)
-pH 7-8
-oxygenated water
-no strong upcurrents to damage coral
-unpolluted (Queensland manages waste)
The units given are the ones specific to the Great Barrier Reef case study
What is coral?
an animal with a symbiotic relationship to the zooxanthellae algae, based on top of a limestone skeleton
What is a mangrove?
coastal forest in brackish water
Brackish water has more salt than freshwater but not as much as seawater
What are the requirements for mangroves to form?
-brackish water
-C-waves to deposit sediments
-no strong currents
-in intertidal zone
-tropical climate
Give some unique adaptations of mangroves trees:
-evergreen + halophytic trees
-aerial roots (support + aids to get oxygen from air during low tide)
-prop roots (support tree in soft sediments)
-sacrificial leaves that excrete excess salt
Too much salt can damage the mangrove trees as it draws water out of its plant cells
Give 3 benefits of mangroves:
-dissipates storm surge energy which minimises coastal erosion + saves money
-builds soil to elevate coastline
-high biodiversity
What are 3 reasons for the removal of mangroves?
-agri/aquaculture (shrimp farming)
-firewood
-land for tourists
Why is coastal erosion faster in some places than others?
-rock type
-amount of POW’s
-wind strength/direction
-sheltering (by wave refraction)
(RAWS)
Define corrosion/solution:
Small rocks being dissolved by acid/chemicals
What do sea walls do?
deflect waves
What do revetments do?
they cause waves to break earlier to minimise erosion to the coastline
