Coasts theory Flashcards
% sediment supply from cliff erosion on beaches
typically 5%
What are Ridges
Slightly raised areas of sandy beaches that run parallel to the shore
What are runnels
small troughs (dips) filled with water that run parallel to the shore
Why steeper gradient of shingle beaches
More percolation of water to less backwash and more swash - net movement of sediment up the beach
What are storm beaches/ridges, why do they form
storm waves hurl pebbles/cobbles to the back of beaches
What are berms
smaller ridges that form at the mean high tide mark due to deposition at the top of the swash
What are cusps
Small, semi-circular depressions formed when multiple waves reach the same point with swash and backwash with the same power.
How are cusps enlarged
They are enlarged as cusps channel swash to the centre of the depression causing a powerful backwash pulling material out of the centre down the beach - enlarging depression
What are ripples
Small grooves in sandbed - develop due to the orbital motion of water in waves that picks up and deposits sand grains, forming small troughs/grooves
Winter beaches
Increased high energy destructive waves caused increased movement of sediment offshore due to erosion, flattening the beach profile. This causes shallower water, increased friction and less wave energy (moving towards summer)
Summer beaches
Increased low energy constructive waves meaning increased sediment moving onshore with deposition. This steepens the beach profile. Causes deeper water, less friction and more wave energy - moving towards winter
When do waves break
When water depth is less than 1.3X wave height
3 main flows of energy
Kinetic, solar/thermal, gravitational
What are sediment cells
Closed system in which sediment in sourced stored and transferred between stores.
a linked system of sources, transfers and sinks of sediment along a section of coastline
How many sediment cells in the UK
11
Are sediment cells truly closed systems
No, small volumes of sediment escape to neighbouring cells during storm events, usually fine sediment like silt/clay
What is dynamic equilibrium of sediment
where input, outputs and flows of sediment are in a constant state of change but remain in balance
Name the 3 processes of a coastal system
Erosion, transportation, deposition
Name types of sediment transportation
Marine - traction, saltation, suspension, solution
Aeolian - same not solution
Types of sediment transfers
Longshore drift
Swash
Backwash
Tidal currents
Sea/ocean currents
Wind (onshore, offshore or along shore)
Impact of oblique winds
LSD
What comes under structure of rocks (geology)
Concordant/discordant
Bedding planes and jointing - landward/seaward/horizontal strata
Fissures and faults - megafaults cause geos and blowholes
3 types of breaking waves
Spilling - steep wave, gentle slope - usually constructive
Plunging - sudden depth change and steep wave - usually destructive
Surging - low wave + steep beach - large backwash - destructive
% sediment supply from offshore on beaches
typically 5%
% sediment supply from rivers on beaches
typically 90%
neap tides
small tidal range, sun and moon not aligned
spring tides
large tidal range, sun and moon aligned
drift aligned beaches
waves at angle to coast, lsd moves sediment along beach
swash aligned beaches
low energy environment (bays), waves parallel to shore
emergent
eg. raised beach, marine terrace, relict cliff
eustatic = sea levels decrease
isostatic = land level increase
submergent
eg. ria / fjord
eustatic = sea levels increase
isostatic = land levels decrease
eustatic
change in sea level
isostatic
change in land level
transgression
eustatic sea levels increase, global, ice caps melt
regression
isostatic rise in land level, emergent landform, eg Scotland
ria
submerged river valley
deep in centre, shallow in cross section
fjord
submerged glacial valley, 1000m deep, cliffs on sides,
shingle beach
shingle = typically 2-200mm
sediment accumulates deposited by rivers, melt water streams, low energy waves.
end of last glacial period = sea levels were high and pushed sediment onshore
raised beach
former shore platform, present beach
tombolo
spit connects to mainland
spit
prevailing winds blow at angle to coastline, creating lsd,extending the beach
offshore bar
sediment eroded by deconstructive waves and carried seaward by backwash
geo
long narrow cleft in cliff face formed by erosion at fault in rock
blowhole
fault in cliff = erosion, sea cave pushed backwards and upwards due to weathering on top of cliff.
