Coastal geomorphology Flashcards
importance of coasts
- population pressures: 3 billion live on coastal zone
- Impact of coastal disasters and storm surges
- sea level rise/coastal erosion: isostatic change/climate change
coast
area between land and sea
- extends inland until meets a different geographical setting
shoreline
precise boundary where water meets adjacent dry land
- not clearly defined
- salt marsh system for land or sea
coastal influences
- wind dominated
- tide dominated
- river dominated
coastal zones
- backshore
- foreshore (swash zone)
- inshore (surf and breaker zone)
- offshore
tidal currents
- driven by gravitational attraction of sun and moon
- amplified by the configuration of the coastline
wave energy
- dictated by wind strength
- may reflect distance over which wave energy has travelled (fetch)
river dominated system
- where wave/tide energy is low
- where major river system deposit large amounts of sediment
- deposition from river system may dominate coastal process
tides
daily fluctuations in the height of the ocean, caused by gravitational attraction of water to moon and sun
- tidal range varies depending on latitude and the shape of the coasts
- cause water level changes at the coast
waves
- transport energy by motion, ultimate sources of wave energy are the sun and winds
- energy and size dependent on wind speed, duration and distance travelled (fetch)
- turbulent airflow = pressure variation = wave formation = disturb airflow = sustain waves
Longshore current
current that parallels shoreline developed by waves coming in at an angle to shore
Types of tides
- diurnal & mixed semi-diurnal
- semi-diurnal tides most places
- spring tides higher than normal tides
- neap tides lower than normal
Tidal ranges
- micro tidal <2m
- meso tidal 2-4m
- macro tidal >4m
tidal range has greater impact than type of geomorphology
tide types
- flood tide, incoming
- ebb tide, outgoing
- maximum tidal velocity is achieved at the tide midpoints (most geomorphological work is done)
Wave types
- spilling: low angle shore, foamy
- plunging: moderate subsurface, or significant changes in depth
- collapsing: steep angle shore, bottom face steepens until collapse, foamy
- surging: long period waves don’t break, typical of tsunami events
constructive waves
- strong swash and weak backwash
- deposition greater than erosion
destructive waves
- weak swash and strong backwash
- erosion is greater than deposition
coastal erosion
- waves are dominant mechanism in coastal erosion, water forced into cracks in rock at high pressures (Cavitation)
- wave energy focused on headlands: prominent cliffs that jut out into deep water
- attacks the sides of headlands & form sea caves, sea arches and sea stack by undercutting
attrition
materials carried by the waves bump into each other and so are smoothed and broken down into smaller particles
hydraulic action
the process involves the force of water against coast. the waves enter cracks in the coastline and compress the air within the crack. when the wave retreats, the air in the crack expands quickly, causing a minor explosion. the process is repeated continuously
corrosion
this is the chemical action of sea water. the acids in the salt water slowly dissolve rocks on the coast. limestone and chalk are particularly prone to this process
abrasion/corrasion
this is the process by which the coast is worn down by material carried by the waves. waves throw these particles against the rock, sometimes at high velocity
wave cup platform
- waves attack the base of the cliff through the process of abrasion, corrosion, hydraulic action and attrition
- over time the cliff will be undercut and a wave cut notch is formed
- eventually the cliff becomes unstable and collapses. further cliff retreat will form a wave cut platform
caves, arches, stacks and stumps
Durdle Door, Dorset
Old Man of How, orkney
preventing coastal erosion
- can establish sand dunes and stabilise existing dunes
- can build seawalls: concrete or riprap structures designed to protect shoreline from waves
coastal management
- no active intervention: nothing is lost if coast erodes
- managed realignment: communities relocated and ban places on re-development
- accommodation (communities adapt and accept risk)
- hold the line (hard/soft engineering measures)
coastal deposition
- occurs when amount of sediment exceeds wave/current ability to transport it
- human activities often induce coastal deposition on purpose or by accident:
- use groins or breakwaters to disrupt longshore current or block waves and induce deposition
beaches
relatively narrow strips of sand, pebble or cobbles deposited along a shoreline
- 90% of beach sediment comes from streams that drain to coast, transported by longshore currents
spit and/or hook
narrow strip of sand that grows across the moth of bay due to longshore current
barrier islands
long narrow island made of sand that flank main shoreline and separate bays from open ocean
- needs abundant coastal sediment and low coastal relief (little or no recent coastal uplift)
tombolo
narrow strip of sediment deposited behind a sea stack by refracted waves
estuary head
where the river enters
estuary margins
the sides
an estuary mouth
opening to the sea
delta development
over time islands of sediment appear in a triangle shape in an estuary
salt marsh development
- intertidal areas of fine sediment transported by water and stabilised by vegetation
4 elements needed for development: - a stable area of sediment covered by the tide for a short time
- a supply of sediment
- low water velocities
- a supple of seeds for the establishment of vegetation cover
Primary coast
shaped by non-marine processes (glaciations, streams etc.)
- often a landscape drowned by rising sea level
secondary coast
shaped by coastal erosion and deposition features outline previously
- primary coasts often have secondary features
plate tectonics
rifted continental margins tend to be dominated by deopositional features
- active margins tend to be dominated by erosional features
summary of coastal features
coastal forms correlate strongly with energy of the processes operating, much depend on:
- geology, topography, Relief & climate
- highly dynamic environment, ever changing
- future sea-level rise will enhance and accelerate the effectiveness of erosion processes
