Coasts part 1 Flashcards
define system
a system of interrelated objects made up of components and processes that are connected together to form a working unit or unified whole
coastal landscape systems store and transfer energy and material on time scales that can vary
inputs to coastal systems
wave energy (kinetic) wind energy (kinetic) tidal energy (kinetic) material on slopes (GPE) material from offshore (GPE) energy from sun (thermal) urban planning coastal management/ defences
outputs of coastal systems
beach erosion by sea beach erosion by wind evapouration erosion of rock surfaces weathering/ erosion of cliffs
throughputs/ stores in coastal systems
beach sandbank near shore sand dunes longshore drift river sediments tidal energy (kinetic) build up of sand below water's surface
when does equilibrium occur on a beach
when sediment added is equal to that being taken away
inputs=outputs
dynamic equilibrium
negative feedback
system undergoes self regulationand changes in order to restore the equilibrium
occurs in a constanly changing system
define sediment cell
stretch of coastline and its nearshore area within which the movement of sediment is largely confined
generally a closed system
(england and wales)
what factors mean there is sometimes sediment transferred between cells
storm events
high tides
dominant winds
what divides up sediment cells
headlands (resistant rock)
topography
wind direction
tides
how many sediment cells are there
11
what are sediment budgets
a coastal management tool used to analyse and describe the different sediment inputs and outputs on the coasts, which is used to predict morphological (shape of coast) change in any particular coastline
do destructive or constructive waves have a bigger input
constructive
potential influences on coastal landscape systems of:
- waves
- winds
- tides
- geology
- global ocean currents
how are waves generated?
by the friction of wind dragging across the surface of water
the higher the wind speed and longer fetch then the more energy they have and bigger they are
what type of energy does a wave have?
GPE
as a result of its position above the wave trough,
kinetic
caused by the motion of water within the wave
formula for the amount of energy in a wave
P= (HxH) x T
P- power - kw/m
H- wave height
T - time between two wave crests (period)
crest
top of the wave
trough
bottom of the wave
wave length
distance between two crests or two troughs
wave height
amplitude- distance of crest to trough
what happens when waves reach the shore?
- the bottoms of the circulating molecules come into contact with the sea floor
- this causes friction which slows the wave down from the bottom
- this causes the wavelength to decrease and the waves start to bunch up
- the top of the wave is still travelling fast and the wave begins to steepen as the base lags behind
- when the depth is 1.3X wave length then the wave topples over, this is when the wave breaks
spilling waves
Steep waves breaking onto gently sloping beaches. Water spills gently forward as the wave breaks. As the wave approaches the shore, it slowly releases energy and the crest gradually spills forward.
Why? • Bottom of the ocean/beach is fairly flat • waves come in and slow down gently • steepen gently • and so break gently • top of the waves spill down the front
plunging waves
Moderately steep waves breaking onto steep beaches. The water plunges vertically downwards as the crest curls over and explodes on the trough. The air under the lip of the wave is compressed, and a crashing sound is often heard.
Why?
• When waves travel from deep water to shallow water very quickly
• and they slow down so fast start causes a motion of water that curls over and crashes down violently
surging waves
Low angle waves breaking onto steep beaches. The wave slides forward and may not actually break, as a result of the water being very deep beneath them.
Why?
• Don’t have much time to break because the transition from deep-water to shallow water is too fast
• So they end up just surging up onto the beach.
• Typically happens in may areas during high tide
describe backwash
after wave broken water moves up beach as swash driven by energy from breaking wave
speed of water slows down through friction until theres no more energy to move forward
then drawn back down beach as backwash
energy to do this comes from gravity and is always perpendicular to the coastline down the steepest slope angle
features of constructive waves
low height low frequency spilling wave strong swash long wavelength
produce hugh and steep beach profiles- storm beaches
features of destructive waves
high height high frequency plunging waves swash less than backwash short wavelength
form low, long length beaches forming berms
sources of sediment
- rivers
- wave erosion
- longshore drift
- aeolian processes
- beach nourishment
- dredging
- constructive waves
sub aerial processes
the processes of weathering and mass movement
geomorphic
the form of the landscape and other natural features on the earth’s surface
mass movement
the movement of surface material caused by gravity eg. landslides and rockfalls
rip currents
an intermitant strong surface current flowing seaward from the shore
swell
a series of mechanical waves that propagate along the interface between water and air and so they are often referred to as surface gravity waves
lithology
the study of the general physical characteristics of rocks
abrasion
waves armed with rock particles scour the coastline as the bits of rock are rubbed together
attrition
rock particles being carried by the water collide and bang together. They progressively get worn away to be smaller and rounder t eventually make sand
hydraulic action
when waves break against a cliff face and any trapped air or water becomes compressed (squashed) at high pressure. When it recedes, the air/ water expands again to widen the crack
pounding
the mass of breaking wave exerts pressure on the rock to cause it to weaken
solution
dissolving of carbonate minerals in coastal rocks which tend to be alkaline. the pH of sea water is usually 7 or 8 so only really happens in small quantities or in scidic polluted areas
open system
freely exchanges matter and energy with its surroundings
closed system
the boundary permits the exchange of energy but not matter with the surroundings
isolated system
no matter or energy can escape or enter
negative feedback
the system’s response in the opposite direction to initial output
self regulating
positive feedback
an increase in output which leads to a further increase in output
example of cell and sub cell
cell- Flamborough Head- The Wash
subcell- Flamborough Head- Humber Estuary
still water level
the surface of the water if all wave and wind action were to cease
period
time required between two successive crests or troughs to pass a fixed point
frequency
number of waves per second that pass a fixed point.
velocity
speed with which the waves are moving a fixed point
ocean waves behave differently depending on…
…the depth of water they’re formed in
what are tides
the periodic variation in sea level that occur primarily because of the Moon’s and the Sun’s gravity
How often SHOULD we get high tides?
12 hours and 25 minutes due to orbit of the moon
we dont always get high tides once a day because:
- varying depths of the oceans
- continents
- shape of coastlines
- interaction of the surface of oceans with atmosphere
tidal range
the difference in height between successive high and low tides
when do spring tides occur?
when the sun earth and moon are aligned
what happens when there is a spring tide?
higher than average high tides and lower than average low tides- increased tidal range
how often do spring tides occur
once every 2 weeks
when does a neap tide occur
when the sun and moon are perpendicular to one another
what happens when there is a neap tide
the height of the high tide is lowered- tidal range reduced
ho often do neap tides occur
once every two weeks
where has the world’s highest tides
The Bay of Fundy- east coast of Canada
because of its distance from the continental shelf edge
need to do about tides a bit more?
to do
material is deposited when…
…there is a loss of energy caused by a decrease in velocity or amount of water
when does marine deposition occur
- when waves slow down after breaking
- at top of swash when water stops moving for a brief moment
- during backwash when water sinks into beach
- in low energy environments sheltered from wind or waves
- beach nourishment (human) sand lost by LSD or erosino is replaced by humans
what does the Hjulstrom Curve show?
the relationship between river velocity, processes and sediment size
when are rocks “under attack”
when it is exposed at the surface it is “under attack” by weathering and erosion
two main geological factors:
1, lithology
2. structures
what is lithology
the physical and chemical composition of the rock, which effects the ability of a rock to withstand weathering, erosion and mass movements.
what are crystalline rocks
have interlocking crystals and are very strong
examples of crystalline rocks
basalt, granite
example of rock with weak bonds
clay
why is clay soft
weak bonds between the particles that make up the rock
example of rock with no interlocking particles
mudstone
what is mudstone composed of
grains
(lithology)
example of rocks that react with acid
limestone and chalk
describe carbonation
Calcium carbonate is soluble in weak acids so is vulnerable to a type of chemical weathering called carbonation. Rain water contains carbonic acid which, over time, will dissolve limestone and chalk.
important properties of individual rock types
- joints
- faults
- porosity and permeability
- beds (eg dip)
- orientation in relation to the coastline
joints
vertical cracks/zones of weakness running through rock and are common in rock like limestone. Joints increase the surface area for physical and chemical weathering and are easily enlarged by solution and freeze thaw. Joints increase the permeability of the rock (secondary permeability).
what processes enlarge joints and the surface area
solution and freeze thaw
faults
a result of tectonic activity to which there has been movement. They are areas of weakness and may slip again. Faults increase permeability of a rock (secondary permeability) making the rock less resistant to chemical weathering.
what is porosity
the ability of a rock to hold water
what is permeability
the degree to which water can pass through a rock
what rock is very permeable and porous
sandstone
why is sandstone both permeable and porous
the spacing between grains and the connected pore spaces
are crystalline rocks permeable or impermeable
impermeable
what does permeable mean
allowing liquids or gases to pass through it
is clay permeable?
no, its impermeable
what are bedding planes
surfaces that separate different layers of rocks. They’re originally deposited horizontally, but may be later tilted
what type of cliff does a horizontal bed crreate
steep sided cliff
when bedding surfaces dip forward, they’re likely to
slip due to gravity and lack of supoprt
what is a discordant coastline?
alternating layers of hard and soft rock are perpendicular to the coastline
what are the features of a discordant coastline?
bays and headlands
what is a concordant coastline?
rocks are parallel to the coastline. Hard rock shields the soft rock from erosion
features of a concordant coastline?
usually a straight coastline
sometimes sea breaks through and forms a cove (a small sheltered bay)
what are currents
currents reflect the movement/flow of water
what effects do currents have on the coast
erosion
deposition
transport
The ocean is an interconnected system powered by the forces of…
… wind, tides, Corolis force, sun and water density differences
what drives surface ocean currents?
wind
surface ocean currents result in what type of movement
horizontal and vertical
factors affecting the size, shape, speed and direction of ocean currents
forces of- wind tides Corolis force sun water density
physical characteristics-
shape of ocean basins
topography
describe horizontal ocean currents
local and typically short term
eg. rip currents
longshore currents
tidal currents
describe vertical ocean currents
upwelling currents
vertical water movemt and mixing brings cold water towards the surface while pulling warmer, less dense water downward, where it condenses and sinks
this creates a cycle of upwelling and downwelling
reversing or rectilinear currents are…
tidal currents that ebb and flow in opposite directions
“floods”
tidal current moving towards the land away from the sea
“ebbs”
tidal current moving towards the sea away from the land
rectilinear tidal currents are typicall found in…
coastal rivers and estuaries
slack water period
when rectilinear tidal currents have a period of no velocity as they move from the ebbing to flooding stage
how do tidal currents occur?
Occur in conjunction with the rise and fall of the tide
The vertical motion of the tides near the shore causes the water to move horizontally creating currents
Are affected by the different phases of the moon.
Relationship between moon phases and tidal and ocean currents
full or new phases– tidal currents velocities are strong – spring tides
first or third phases– tidal current velocities are weak– neap currents
The effect of Gyres/Coriolis Force on coasts
Warm ocean currents transfer heat energy from LOW LATITUDES towards the poles. In the northern hemisphere they particularly effect WESTERN-FACING coastal areas where they are driven by onshore winds. COLD ocean currents do the OPPOSITE, moving cold water from polar regions towards the equator; these are usually driven by offshore winds, and so tend to have less effect on coastal landscapes. The transfer of heat energy may be significant, as it directly affects air temperature and sub-aerial processes.
what is the main source of sediment to the coastal budget
rivers
