coasts Flashcards
wave formation
energy transferred from air to water, shelving increases friction, wave breaks
coastal defences effect on physical geo.
disrupt physical geography processes, e.g. walls, groynes
waves change direction, energy taken elsewhere
littoral zone and subdivisions
offshore (furtherest) - sea away from land
nearshore
foreshore
backshore (closest) - waves only reach during high tide
coast/land
primary coast
dominated by land-based processes
e.g. deposition from rivers, volcanic lava
zavodovski island
secondary coast
dominated by marine erosion / deposition
e.g. slapton
coastline morphodynamics
things that change a beach are constantly changing, the way different factors make a coastline unique and how these factors are constantly changing.
short term processes: rivers, waves, tides
longer term processes: geology, sea level change
wave size
wind strength
wind duration
water depth
wave direction
percolation
downward movement of water through soil, sand, pebbles
constructive
low height, low wavelength 6-8 per min uninterrupted swash, nearshore strong swash steeper beach gradient change over long distance
destructive
high height, short wavelength 13-15 per min slower waves approach steep beach still circular motion stronger backwash gradient change over short distance
littoral zone
near shore area where sunlight penetrates sediments, allowing for aquatic life to flourish, but faces continuous change
sea-level change
geology of cork coastline:
orientated 90 degrees perp., alternating hard/soft rock = elongated narrow bays
hard resistant areas = detached islands
storms = long fetch, help rivers erode = form valleys
sea level rise = valleys drowned
headland + bay = exaggerated
role of wave refraction
deep water wave crests - parallel to the coastline
headlands: wave crests curve, refract, concentrated on headlands, spread outwards to the bays
headlands - accelerate erosion
material - deposited in bay
coastline: straight overall. headlands erode, material deposited in bays
tectonic activity on beach shape
push sedimentary rock up from seabed - e.g. limestone
can fold them - plate collisions = creates weak points for waves to exploit
magma may have risen to the surface and cooled = igneous rock
sea removes layers above it
igneous rock exposed and resisting wave erosion
= gradually get a straight coastline
rias
drowned river valley due to SLR
dalmatia coastline
concordant coastline
drowned by SLR
limestone geology
horizontal strata - oldest at bottom, youngest at top
tectonics - compressed and folded layers - anticlines and synclines
sub-aerial erosion - eroded starta in weak places
rivers erode synclines
long narrow islands are left
haff coastline
long sediment ridges
sand dunes
parallel to coastline
series of lagoons between ridges and shores
marine erosion
synclines, beneath
river erosion
anticlines and shapes landscape
new zealand
convergent plate boundary
7.8 magnitude wave - 4 different faults broke at once
sea bed is now 2m higher
marine animals died
3km/second
6m uplift on one side, 2m uplift on other
new foreshore
isostatic change
heavy ice pushes land downwards, melting ice means that land rebounds back
new cliffs formed through erosion, old fossil cliffs remain
isostatic readjustment
soft vicious mantle, parts of crust respond to change
norwegian fjords
submergent coastline as a result of eustatic SLR
200km inland
fracture system in bedrock
entrance at seaward end is shalower
gravel and sand deposits = made certain areas of fjords shallower
wave-cut platform
sloping rocky shelf found at the foot of a retreating cliff and exposed at low tide
periglacial
permanently frozen ground
fjords
submerged u-shaped valley that has been over-deepened inland
rock lip threshold - seaward entrance
eustatic rise/fall
change in global sea level
Louisiana
Mississippi river flows into Gulf of Mexico
depositional coast - marshes, swamps, barrier islands
huge levees and engineering projects to protect NO
vulnerable to storm surges, global sea level rise, isostatic tectonic uplift
eustatic fall
ice sheets formed during glacial period
evaporated water locked up as ice
fall in SLR
offshore bars raised beaches fossil cliffs but... storm surges? tides? tectonics?
sea level changes daily
high and low tides alter local sea level
atmospheric air pressure = low pressure, slight rise
winds = wave height varies
marine regression
eustatic fall and isostatic fall - former seabed exposed = emergent coast
marine transgression
eustatic ride and isostatic rise - areas of land flood = submergent coast
North Antrim Coast rock types
igneous: (impermeable)
basalt, dolerite and gabbro, granite, basalt
strong, hard erosion-resistant rock
few joints, limited weaknesses, erosion can’t exploit
sedimentary: layers of rock formed over time sandstone (permeable) animals and plants moderate/fast erosion rate young rocks = weaker shale - most vulnerable
metamorphic: (impermeable)
intense heat/pressure
slate, schist, marble
resistant to erosion
foliation - crystals in one direction = weakness
folded + heavily fractures
folding = cracks, water gets in, permeable
ancient limestone(permeable): more resistant recently erupted volcanic lava = weaker, easily eroded
permeability = groundwater flow weakens rocks, exploiting joints and structure, binding materials
high pore water pressures within cliff = reduce stability
low seaward dip but places with landward dip
entablature
unconsolidated laterite, more permeable, stores water
water sits
water builds up in entablature as it travels slowly in the colonnades, so gets heavier and rock materials fall = mass movement
colonnades
columns, water goes down cracks and faults
water can get through but very slowly
West Africa (Guinea)
700m of erosion
10cm of SLR since 1950
1m SLR by 2100
urbanisation high along coast: fishing, tourism
stormy months
loss of mangrove forests: harvested as fuel wood
rainfall
intensive sand mining in mangroves and rivers
gold and diamond mining along rivers, gravel extracted from rivers each day but not returned
use gravel to build local houses
sand = removed from coastlines for construction
sea walls = too expensive
don’t do beach nourishment
major storms
local construction: seawalls and revetments stop sediments being moved along coast
tourist resorts = swept away
saltwater intrusion - destroying marine habitats
beach dunes reduced
natural vegetation removed or dislodged
steep cliffs - from weathering/undercutting
Holderness
holderness coast
50 properties
access road
soft boulder clay cliffs
1-2m/ year rate of erosion
coastal management scheme: £2million
2 types of hard engineering: Norwegian granite rock armour along base of cliff
two rock groynes
stopped beach material being moved south along the coast
left area south of coast: Withensea unprotected
increased erosion in south
mappleton and cliffs no longer at great risk
Trinidad and Tobago
small island, developing state
low lying, susceptible to 0.06m/year rise in SL
70% population live/work on coast
winter storms from Atlantic= higher swell waves
southerly LSD, high erosion rates: Coco Bay
coastal flooding along 20km Manzanilla beach, cut off roots
weak sandstone + metamorphoc rock
there are vital sites of oil industry= main source of GDP and exports
economic losses:
3rd largest economy in America after US and Canada
dependent on petrochemicals - 40% GDP, 80% exports
natural gas pipelines
infrastructure loss
300m major road access destroyed due to strom 2014
luxury beach homes - £700k
400,000+ tourists
$5.8 million spent on rehabilitation work
engineering firms + academic expertise
social losses:
loss of coconut plantations, watermelon+ vegetable cash crop
transport access affected - can’t access oil industry/tourist
value of coastal homes = likely to decrease overtime
damage to existing hotel and tourist industry
some owners can afford a rubble war, some can’t - rich/poor divide
environmental loss:
damage to turtles that may encourage ecotourism
ecosystems can adapt - so small scale loss
lack of understanding with regards to beach dyanmics
