Coastal Systems AW Flashcards
What are the 4 factors of dynamic equilibrium in a coastal system?
-supply of sand
-the energy of waves
-changes in sea level
-the location of the shoreline
Explain dynamic equilibrium in terms of waves and beach erosion
The summer has more constructive waves, which have a stronger swash than backwash so more material is deposited, the beach grows and gets steeper.
The winter has more destructive waves so the swash is weak and the backwash is strong so more erosion and the beach shrinks.
Define dynamic equilibrium
A system is subject to continuous change which counteracts the changes to stay within set parameters
Whats negative feedback ?
The system counteracts the change, lessening/ reversing it’s effect
Whats positive feedback ?
System reacts and accelerate the change and effect on the environment
What is an example and positive feedback?
The suns rays warm the earth melting ice in the arctic/antarctic (which has high albedo effect and reflects sun’s rays cooling the earth) increasing the size of the dark oceans (which have low albedo and absorb more heat) warming the earth melting the ice faster
What is an open system ?
- add example
A system allows mass and energy to flow across the system boundary.can be flow of matter.
- the sun
- the hydrosphere
- the coast
What is a closed system ?
-add example
The system allows energy flow across system boundaries, but no flow of matter.
- the earth
- the geosphere
What is a littoral cell ?
(Sediment cell)
A section of coastline where sediment is recycled but not lost or added to
Define sediment budget
The amount of sediment on a beach.
(The net value between amount of input and output)
What is a positive beach budget ?
Excess sediment on the beach
What is a negative beach budget ?
When there is a sediment deficit on the beach
What is a neutral sediment budget ?
When there is no difference between the input and output quantities of sediment.
What are some inputs of a sediment budget ?
Landward Material inputs
- Mass movement
- Cliff erosion
Marine inputs
- Longshore drift
- Wave deposition
What are some outputs of a sediment budget in a simple beach system ?
Landward Material outputs
- Sand dune development
Marine outputs (flows)
- Waste removal
- Longshore drift
What is the store in a simple beach system sediment budget ?
The Beach
Give an example of negative feedback
Cliff erosion leads to slumping, so cliff material falls in front of the cliff, protecting it from erosion until the waves can remove and erode the slumped material
Give an example of negative feedback
Cliff erosion leads to slumping, so cliff material falls in front of the cliff, protecting it from erosion until the waves can remove and erode the slumped mayerial
Give a beach example of a positive feedback loop
Waves remove vegetation from rocks and cliffs, so there isn’t anything to protect them. The cliff erosion speeds up.
What is a penantuala ?
Land that sticks out and is surrounded by sea on 3 sides
Wind is a transfer of energy via the atmosphere. How is wind created ?
Via a pressure gradient. Air moves from areas of high pressure to areas of low pressure. The larger the difference in pressure, the faster and more powerful the wind.
What’s the average global atmospheric pressure ?
1 bar or 1000 millibars
What causes different pressures ?
The sun heats air, hot air rises, creating low pressure.
How large are the pressure differences in the atmosphere ?
There can’t be large differences in pressure because gas moves and there is no physical barrier stopping it. 980mb is very low pressure, causes strong winds
Define pressure gradient
How fast the pressure changes in different areas
What is atmospheric pressure ?
The weight of the atmosphere on the ground
What are wave features
Add diagram
Describe a constructive wave
Strong swash and weak backwash so material is deposited on the beach, making it bigger and steeper
In the summer, mostly
Low wave height, long wavelength - long rolling waves.
Describe a destructive wave
High energy waves, tall in height.
Weak swash and strong backwash, so material is transported down the beach.
Mainly in the winter.
What is wave refraction?
. Convergent and divergent
When waves are around a headland they tend to bend, as waves approaching a headland hit shallower waters sooner than the rest of the wave ( in the bay which is in deeper water)
The wave by the headland in shallower water experiences friction with the sea floor - slowing. The edges of the wave move faster and the wave converges around the headland.
In the bay the opposite happens and the edges of the wave are in shallower water nearest the headland and friction slows them (slower relative to wave in deeper bay). Thile wave diverges into the bay.
What is Swash aligned ?
Where the waves hit the beach at 90°
What is drift aligned ?
Where the prevailing wind is at a significant angle to the beach so waves hit the beach at an angle and cause longshore drift up the beach
What’s a discordant coastline?
Where the coast is made up of bands of multiple types of rock perpendicular to the coast (of different densities leading to the formation of headlands and bays)
What’s a concordant coastline?
Beds of rock are parallel to the coast so the coastline has the same type of rock along the coast.
What are tides caused by?
Tides are caused by the gravitational pull of the sun and moon.
The moon has the greatest influence due to distance, oceans closest to the moon have an outward bulge, causing high tides ( low tides is the draining of water from areas)
What is a neap tide?
What causes them?
The highest low tide and the lowest hight tide in a year.
Caused when the sun and the moon are at right angles and interfere with each other.
What is a spring tide?
What causes them?
Highest high tide and the lowest low tide
Highest tide where the earth is between the moon and sun.
How long is between high and low tide?
How many tides are there per day?
There’s 6 hours between high tide and low tide.
4 tides per day, 2 high and 2 low tides.
Define tidal range
The difference between high tide and low tide
What is macrotidal?
When the tidal range is larger than 4 metres
What is mesotidal?
When the tidal range is between 4 and 1.8 metres
What is microtidal?
When the tidal range is less that 1.8 metres
What influences tides?
. Gravitational pull of sun and moon
. Weather conditions
. Ocean bed
. Rivers and shape of coastline
What causes currents?
Water in the ocean is different densities in different areas, causing currents as high density water moves to low density areas.
What causes different water densities in the ocean?
. Saltiness of water (from rocks with sodium dissolved
. Temperature
What are longshore currents caused by?
Longshore currents are caused by prevailing winds hitting at a non 90° angle
(A near shore current that is very localised and small scale)
What’s an upwelling current?
Where water comes up to the surface.
(A near shore current that is very localised and small scale)
What is a rip current
Rip currents are strong, localised underwater currents that occur at some beaches. Formed when a series of plunging waves cause a temporary build up of water at the top of the beach, met with resistance of breaking waves the backwash is forced under the surface.
What is the gulf stream?
A large current that comes up from Mexico, the water is warm and less dense. Moves 4 billion cubic feet of water per second.
What is the great ocean conveyor belt?
Created by the sinking and falling of ocean currents. It transfers heat and takes 1000 yes for water to move through the conveyor belt.
What is a storm surge?
When meteorological conditions giving rise to strong winds can produce much higher water levels than those at high tide.
Very low pressure systems (e.g. hurricanes) take the weight of the atmosphere off the ocean allowing every water molecule to take up more space, ocean rises.
Where is the back shore zone?
The area between the highwater mark and landward limits of marine activity (changes only occured during storm activity)
Where’s the foreshore zone?
Area between low water mark and high water mark. The most important place for marine processes.
Where’s the inshore zone?
The area between the point where waves don’t have any affect on the land below and the low water mark.
(Foreshore + inshore = Nearshore)
What’s the Nearshore zone and the subsections?
Area seaward from the high watermark to the area where waves begin to break.
Including:
. Swash zone
. Surf zone
. Breaker zone
What’s the swash zone?
Subsection of Nearshore zone. Area where turbulent layer of water washes up on the beach after the wave breaks.
What’s the surf zone?
Subsection of Nearshore zone. Area between the point where the waves breaks and where the waves moves up the beach as swash in the swash zone.
What’s the breaker zone?
Subsection of Nearshore zone. Area where the waves begin to break when approaching the beach (usually water depth is 5-10 metres)
What’s the offshore zone?
Area past the point where waves stop impacting the sea bed below, deposition of sediment is limited.
What are Sediment cells?
Sediment is moved around distinct areas/ cells, normally separated by a distinct feature e.g. a headland. There regarded as a closed system as no sediment is lost or gained (theoretically). They are very large and may have sub cells within them.
What are the problems with the concept of sediment cells?
In theory the sediment is lost or gained but in reality small bits of sediment are easily transferred to different cells.
What is a fetch?
The fetch is the uninterrupted distance that wind blows over a body of water from one obstacle to another, in the same direction.
What effect does the fetch have on waves?
Work is done as wind blows over the water called fictional drag, the longer the fetch the bigger and more powerful the waves are (due to more energy being transferred).
How far down do waves cause movement?
Waves cause surface water movement and 5 - 10 metres down water doesn’t really move
What’s motion do waves move in?
Waves are just energy passing through water in circular motions. The water stays in pretty much the same place as the wave moves. This motion causes air to get trapped making it less dense than the rest of the water so it stays on top.
What happens to the orbital motion of waves at the shore?
At the shore the water gets shallower and the orbital motion is broken/ disrupted by the sea floor. The bottom of the wave slows due to friction forcing the crest higher, causing it to crash down. The wave breaks.
What are datums?
Scientists use datums as a normal and use it as a reference to see how much water levels rise and fall
What causes currents?
They are driven by wind, tides, shape of land and temperature
How do you measure currents?
Main components are speed and direction, put an object in the ocean and record how long it takes to get to a certain place
How do you measure tides?
Air acoustic and pressure systems to record changes in water levels
Why do people study tides and currents?
Need knowledge of them to
. Aid navigation
. Keep people and the environment safe
. Need to know the water levels for boats to pass under bridges
What is the intertidal zone?
The zone between high and low tides, it’s a harsh and unforgiving habitat.
What are the 4 subsections of the intertidal zone?
. The spray zone
. High intertidal zone
. Mid intertidal zone
. Low intertidal zone
Describe the spray zone.
Mostly land, rarely submerged in ocean (only very high tide or storms), wet from waves and wind blown spray
Life like litchens and periwinkle snails
Describe the high intertidal zone.
Out of water in long stretches but submerged during daily high tides.
Life like crabs, seaweed, barnacles
Describe the mid intertidal zone.
Submerged other than low tide.
Life like muscles, snails, sea urchins
Describe low intertidal zones.
Submerged and only exposed during lowest spring tides (twice a year)
Life like crabs, urchins, kelp, sea stars
What can disrupt dynamic equilibrium?
Physical: storms
Human: swa walls, groynes, gabions, mining, people using the beach
What’s the difference between erosion and weathering?
During weathering rocks stay in situ (same place).
List 4 types of erosion
Hydraulic action
Abrasion
Attrition
Solution (corrasion)
What two processes wear away the coast?
Marine processes
Sub aerial process
What are marine processes
Hydraulic action
Abrasion
Attrition
Solution
Wave quarrying
Wave Cavitation
What is wave quarrying?
What is cavitation?
Wave quarrying - Breaking waves trap air, water compresses air into any gaps in the rock creating enormous pressure, weakening the cliff, chunks can be easily removed.
Cavitation - waves vibrate the cliff and break off chunks.
Define weathering
The wearing or breaking down of rocks while they are in place
What is Biological weathering
Weathering from nature and animals.
E.g. from roots of a tree getting into cracks in rocks, widening them and breaking off chunks. Or a rabbit burrowing a hole.
What is mechanical weathering
Physical processes of weathering.
Freeze thaw- water gets into cracks top freezes first creating a ‘plug’, the water below freezes, expanding and can’t expand up, creates pressure on the crack widening it.
Wetting and drying - porous rocks/clay. The rocks expand when wet and when dry they contract causing cracks to form
Salt Crystalisation - salt crystals are deposited in cracks and they accumulate overtime applying pressure to the crack
What is chemical weathering
Carbon dioxide dissolves in rain making it slightly acidic- can react with rocks like limestone - weathering them.
What is soil creep?
A very slow movement on a gentle slope when soil expands and contracts as it wets and dries. When it drys it contracts vertically and when in wets it expands at right angles.
Define landslides
Material falls down along the ground
Define rockfall
Landfalls vertically
Define mudflows
Saturated soil flowing down a slope
Define rotational slumping
Heavy rain it absorbed by loose material that makes up the cliff (usually glacial till) . The cliff face becomes heavier and eventually it separates from the material behind. Lubricated by the rain. Falls in a rotational curved motion
What factors effect the rate of erosion at the coast?
. Geological structure (cracks, rock strata, bedding planes)
. Presence of a beach (they absorb wave energy, protects cliffs from erosion)
. Sub aerial processes ( weathering and mass movement weaken cliffs)
. Waves and fetch (size and power of waves)
. Rock type (physical strength)
. Coastal management (can slow erosion)
What is a discordant coastline?
Coastlines with different rocks perpendicular to the coast, hard and soft.
Landforms like headland and bays.
What is a concordant coastline?
One type of rock parallel to the coastline.
How is a wave-cut platform formed
A wave-cut notch is created by erosional processes like hydraulic action and abrasion.
The notch becomes larger and the cliff is unstable and collapses.
Cliff retreats inland.
Eroded material is transported away.
Leaving a wave-cut platform.
Processes repeat.
(Wave cut platforms slow cliff erosion)
Describe longshore drift
The prevailing wind cause waste to hit the beach at an angle.
The wave carries sediment transporting it up the the beach, gravity pulls the water back down the beach at a right angle (backwash). This causes the Sediment to move up the beach in a saw tooth pattern.
What are Aeolian processes?
The transportation and deposition of sediment via wind.
Describe three physical weathering processes.
-Freeze thaw
water gets to cracks in the rock.
top layer freezes first as it’s more exposed
•the bottom layer of water then freezes and expands (ice is 9% bager time water as it traps air) and can’t expand up because top ice blocks it in so expands widening the crack.
the ice then thaws and the water doesn’t fill the large cracks now. so more water fills. Process repeates
-Salt Crystalisation.
.Salt crystals are deposited in cracks, over time the Salt accumulates and applies pressure to the crack.
-wetting and drying of rocks
water absorption to (clay rich rocks or porous rocks. Cause them to expand then contract. When they dry, it causes cracks to form.
What are the 4 main types of mass movement?
Creep- soil creep
Flow- mudflow
Slide- rock slide, rotational slumping
Fall- rockfall
Factors that can cause landslips and slumping.
Rock type - bedding planes, competence of rocks (high/strong=slipping, low/weak=slumping), weathering weakening rocks.
Slope angle- the steeper the more likely to fall.
Water- adds weight, lubricant.
Human contributions- building on a slope, removing vegetation (which intercepts water and binds soil).
What’s soil creep/ solifluction
Very slow continuous movement of individual soil particles down slope in the presence of water and weathering processes.
Particles change size when they’re freeze and thaw
Its very slow over thousands of years solifluction is freezing and thawing and soil creep is wetting and drying
What is mudflow
Is a form of mass movement where large quantities of fine material flow downhill, soil become saturated and excess water stays on the surface, it’s very fluid and flows down
What are landslides
A form of mass movement on Cliffs made from softer rocks or deposited material, like glacial till, the slip is as a result of failure within the cliff when lubricated usually following rainfall
It’s a fast and short movement
What’s run-off
Water running over the surface of land, it’s presence aids mass movement.
What’s rockfall
A form of mass movement where individual rocks fall by themselves from the air very fast and short movements. It’s dry.
What’s land slip/slumping
A form of mass movement where soft material is on more resistant material and moves down in a rotational movement
What’s the difference between weathering and mass movement
During weathering the material stays in situ, but in mass movement it moves and is caused by Gravity.
Describe the difference between back wash on a sandy beach and a pebbley beach
Sandy beaches have a shallow gradient than stony. As sandy beaches can’t support a stepping gradient
Sandy beaches have less percolation (less water to seep into the sand so there is a strong backwash)
Stony beaches have high percolation, so more water seeps into the beach, so a weaker backwash and a steeper beach.
What’s a berm
Beach ridges built be constructive waves
What’s a runnel
When a ridge forms at the low watermark, the water can’t flow over the bump so the water flows up the beach.
How’s the spit formed?
1.The prevailing wind hits the beach at an angle causing the swash to go up the beach as an angle carrying sediment and then down the beach perpendicular as backwash
2. this causes longshore drift carrying sediment up the coast then there’s a sharp bend in the coastline and sediment is to deposited offshore
3. shallow water gives the beach support and the beach builds up and spit extends to the sea
4. due to prevailing wind the beach recurves parallel with the prevailing Wind called a hook
What is a compound spit?
This is where the spit has multiple hooked ends and recurves. After each hook, there are changing conditions, which causes the spit to grow further out, and then the prevailing wind causes it to hook and recurve again.
For example, increased wind strength, reduced water depths, Leeward of the spit, reduced river flow, and increased river load of sediment.
What are cusps?
Semicircular shapes depressions which form when waves break directly onto the beach and the swash and backwash and strong
What is a offshore?
At high tide, water gets deeper (5 - 10m) where not much water movement occurs, and is a low energy environment, so sediment is dropped. This forms an offshore bar.
What’s a ridge?
What is a tombolo?
A tombolo is formed when a spit connects the mainland coast to an island. A spit is a feature that is formed through deposition of material at coastlines. The process of longshore drift occurs and this moves material along the coastline.
(A beach connecting and island to land)
What’s a barrier beach (same as a bar)
A sand ridge that’s above the surface of the sea and runs parallel to the shore across a lagoon. Connecting the two sides ( a spit that meets both sides)
What’s a barrier island
When a barrier beach is completely separated from mainland
