Coasts Flashcards
What are submergent coastlines?
Being submerged, relative sea level rising, estuaries formed in drowned river mouths eg Dalmatian Coast, Croatia
What are emergent coastlines?
Land emerging from water, relative sea level falling, tectonics or isostasy responsible for most types eg Isle of Arran, Scotland
What are coastal plain coastlines?
low energy coasts where depositional landforms found, likely made of sedimentary rock eg Bamburgh beach
what are rocky coastlines?
high energy coasts where erosional landforms found, likely made of igneous or metamorphic rock eg Bedruthen steps
What are high energy coastlines?
Exposed coasts facing prevailing winds with long wave fetched resulting in powerful waves, generally have rocky coasts, where rate of erosion exceeds rate of deposition eg Old Harry’s rocks
What are low energy coastlines?
Sheltered coasts with limited fetch and low wind speeds resulting in small waves, generally have sandy coasts, where rate of deposition exceeds rate of erosion eg Flamborough head
what are depositional coastlines?
Developed where sediments accumulate either from a local source or after being transported to the area in rivers and glaciers or by ocean currents and waves; these include deltas, mangrove swamps, salt marshes, barrier islands, and beach-sand dunes eg Spurn head
what are erosional coastlines?
Developed where active erosion by wave action occurs or where rivers or glaciers caused erosion when sea level was lower than it presently is, includes cliffs or rocky shores eg Lands end
what are primary coastlines?
Dominated by land based processes such as deposition at the coast from rivers or new coastal land formed from lava flows.
what are secondary coastlines?
Dominated by marine erosion or deposition processes where sea movement causes accumulation of ocean sediments in a single place. Examples include barrier islands, mud flats and coral reef ecosystems.
what is the tees exe line?
a line dividing the uk, to the north/west of it rock is harder, older, igneous or metamorphic, and high energy rocky coasts and mountains are found, to the south/east rock is softer, younger, sedimentary, and lowlands and low energy coastal plain coasts found
give examples of sedimentary rock
sandstone, limestone, shale
give examples of igneous rock
basalt, granite
give example of metamorphic rock
marble, slate
what 4 factors affect coastal erosion?
rock type, rock structure, wave type, coastline shape
what is a discordant coastline?
rock layers are perpendicular to the coast so headlands and bays form
what is a concordant coastline?
rock layers are parallel to the coast so coves form
how does vegetation stabilise sand dunes?
winds move sediment up the beach by saltation, which gets trapped by seaweed at the strand line, forming an embryo dune which is colonised by pioneer species eg lyme grass, stabilising the dune. this process is repeated forming more dunes - fore dunes and yellow dunes (marram grass comes in here) and grey dunes. further up the beach, nutrients, moisture, hummus, stability and ph increase while salinity decrease, so more plants outcompete the pioneer species until climatic climax is reached
how does vegetation stabilise salt marshes?
mud is deposited in low energy environments, and salt tolerant plants begin to colonise and stabilise the mud flat, then halophytes eg cordgrass slow down tidal flow, trapping more mud and silt, and as mud rises it is less covered by water so plants eg meadowgrass outcompete pioneer species and less salt tolerant plants can survive further up the marsh as it becomes less saline, more fertile and has more organic matter
describe constructive waves
stronger swash than backwash so they deposit sediment, less frequent, creates berm and gently sloping beach, long wavelength, dominate in summer
describe destructive waves
stronger backwash than swash so erode sediment, frequent, destroys berm and creates offshore bar, short wavelength, sloping beach, dominate in winter
explain hydraulic action
waves crash against cliff trapping air in rock joints, which compresses and expands when wave retreats, weakening rock joint
explain wave refraction
the process by which wave crests bend to be parallel to the coast. waves move slower in shallower water, so wave crests bend until all parts of the wave are at an equal depth, resulting in the convergence of wave energy on headlands, and diverging at bays, so more erosion at headland
explain the sediment cell
sediment cells are systems of sources, transfers and sinks. there is a sediment budget within a cell, and cell act to reach dynamic equilibrium - if budget falls, transportation and erosion occurs (pos feedback), if budget increases, more deposition occurs (neg feedback)
mechanical weathering
freeze thaw, salt cracking, wetting and drying
explain salt weathering
when salt water evaporates, it leaves salt crystals behind, which can grow over time causing stresses in the rock, causing it to break
biological weathering
plants growing roots into cracks in rock
chemical weathering
acid rain and sea spray
explain soil creep
the slow downward movement of individual soil particles
what is weathering
the gradual breakdown of rock in situ
what is mass movement
the movement of material downslope due to gravity
explain slumping
- Slumping causes rotational scars, and repeated slumping creates terraced cliff profiles.
o Slumping occurs in more saturated conditions, on moderate to steep slopes, and is common where softer, more permeable materials overlie harder less permeable rock.
o Rock slumps down along a curved rock plane.
o There is a rotational movement in slumping which exposes a rotational scar - a fresh, curved, unvegetated rock surface on a cliff face.
o This forms terraced cliff profiles
explain rockfalls
- Rockfalls form talus scree slopes.
o Rockfalls commonly occur when strong, steep cliff faces with lots of jointed are exposed to mechanical weathering, on slopes over 40º.
o The material that breaks off the cliff falls down to form scree (also known as talus) at the bottom of the cliff.
explain rock slides
- Rock slides form talus scree slopes.
o Jointed rocks, or cliffs with bedding planes roughly parallel to the slope or cliff surface, are susceptible to landslides.
o Blocks of rock move downslope on a slip plane.
o Scree is formed at the foot of the slope.
explain isostatic sea level change
- During an ice age layers of snow fall and build up on the land.
- The snow then freezes into ice
- The weight of the land causes the crust to ‘sink’ under the weight (isostatic subsidence).
- This causes the sea level to rise.
- The ice begins to melt into the sea at the end of a glacial period
- Reduced weight of the ice causes the land to readjust and rise (isostatic recovery)
- Isostatic recovery is a slow process which takes place over numerous years.
- The sea level decreases.
explain eustatic sea level change
- Millions of people drive petrol and diesel cars everyday
- Increasing concentrations of Greenhouse gases are present in the atmosphere
- The enhanced greenhouse effect - the atmospheric temperature rises over time
- This high temperature causes the Antarctic ice sheets and glaciers to melt
- This increases the volume of water in the oceans
- World average sea levels rise
- This floods low-lying areas, for example the Maldives and the south of Bangladesh
explain steric sea level rise
- Temperature of the water increases.
- This means the particles have more energy.
- This causes the particles to move faster.
- This causes them to spread out more.
- Therefore the water has more volume.
- And hence has expanded.
- This causes the sea level to rise.
- This accounts for 70-75% of Sea Level Rise.
what are relict cliffs?
old cliffs displaying features such as caves, arches and stack
what are raised beaches?
Areas of former wave-cut platforms and their beaches which are at a higher level than the present sea level due to isostatic uplift. eg Isle of Arran
what is a ria?
a drowned river valley, flooded as sea levels rise, while higher land remains exposed eg kingsbridge estuary, devon
what is a fjord?
a drowned glacial valley - as sea levels rise, U shaped valleys often 1000m deep left by glaciers are submerged eg Loch torridon, Scotland
what is a fjard?
a flooded glacial lowland - formed by the submergence of formerly glaciated valleys
what are dalmatian coasts?
when synclines on a concordant coast are eroded leaving islands where anticlines are eg Croatia
factors affecting coastal recession
- Storms
- High energy coast
- Destructive waves - long fetch
- Soft/weak geology
- Sea level rising/ submerging coast
- Lots of sub-aerial processes - weathering and mass movement
- Narrow beaches
why is bangladesh at risk from floods?
sediment starved by dams, mangroves removed, isostatic readjustment causing it to be pushed down as himalayas spring up
give methods of hard engineering
sea wall, groyne, revetments, rock armour
give methods of soft engineering
beach nourishment/replenishment, managed retreat
what is integrated coastal zone management (ICZM)
managing complete sections of coast as a whole rather than by individual towns, bringing together all players
what is a shoreline management plan (SMP)
when all local interest groups are consulted and plans are decided on - either do nothing, hold the line, advance the line or retreat the line
How do spits form?
Spits are formed where the prevailing wind blows at an angle to the coastline, resulting in longshore drift, which causes sedimtent to be deposited at the end of a beach, forming a spit
How do tombolos form?
Wave refraction around an offshore island creates an area of calm water so deposition occurs between the island and the coast. LSD also occurs.
How do bars form?
A spit grows so long that it extends across a bay eg Chesil beach
How do cuspate foreland form?
Commonly accepted answer is that two spits are growing from opposite directions eg Dungeness, Kent
