Systems And Processes Flashcards
Name the two types of geomorphological processes
Marine processes
Sub-aerial processes
Define marine processes
Coastal processes that link with the sea
Eg waves, tides, longshore drift.
Define sub-aerial processes
Land based processes that shape the coastline by sub-aerial weathering or mass movement
Name the types of marine erosion
Hydraulic action Wave quarrying Abrasion Attrition Solution
Define hydraulic action
The weakening of rocks by the force and pressure created by waves hitting them
Define wave quarrying
The weakening / breaking off of the cliff face when waves compress air into fissures / joints, which is quickly released when the waves withdraw.
-> like an explosion
Define abrasion
The weakening of rocks by sediment in the sea being thrown against the cliffs / wave cut platform.
Define attrition
Material in the sea wear each other down as they collide in the water.
Define solution
When acidic water dissolves calcium based rocks eg limestone.
-> usually a mixture of sea water and fresh water in localised areas.
How can carbon based rocks be eroded by solution process?
Carbon based rocks eroded by rainwater flow from the land -> pH of this water is usually slightly acidic
How can salt from sea water residue erode rock as part of the solution process?
Sea water residue in rocks evaporates -> salt crystals form -> expand -> weaken / break rock
Name the factors that affect the rate of marine erosion
Wave steepness Breaking point Fetch Sea depth Coastal configuration Beach presence Human activity
How does wave steepness affect the rate of marine erosion?
Steeper waves -> higher energy -> more erosive
How does breaking point of waves affect the rate of marine erosion?
Closer the waves break to the shore -> more they erode the rocks (haven’t lost energy)
How does fetch affect the rate of marine erosion?
Waves that have travelled a long distance before reaching the shore -> more energy -> more erosive
How does sea depth affect the rate of marine erosion?
Steeper-shelving sea bed by the shore -> higher, steeper waves -> more energy -> more erosive
How does coastal configuration affect the rate of marine erosion?
Headlands attract wave energy through refraction.
Concordant / discordant -> resistant/non rock exposed
How does beach presence affect the rate of marine erosion?
Beaches dissipate wave energy -> lower rate of erosion.
- Steep, narrow beaches -> dissipate flatter waves.
- Flat, wide beaches -> dissipate high, rapid energy output -> because energy is spread out over larger area.
- Shingle beaches -> dissipate steep waves -> due to friction, percolation.
How does human activity affect the rate of marine erosion?
Increase erosion rate -> removing protective sand / shingle.
Decrease erosion rate -> installing sea defences (these may increase erosion elsewhere).
Define lithology
Refers to the characteristics of rocks
Esp resistance to erosion, permeability.
Define differential erosion
The variation in rates that rock types erode
Eg at discordant coastlines.
Define concordant coastline
When rock types run parallel to the shoreline
Eg Lulworth Cove
Define discordant coastline
When rock types run perpendicular to the shoreline
Eg Swanage Bay
Define ‘dip’ of rocks
Refers to the angle of rock layers in cliffs -> affects steepness of cliffs
Which direction of ‘dip’ leads to steep cliffs?
Rock strata = horizontal / dipping inland -> steepest cliffs
Which direction of ‘dip’ leads to sloping cliffs?
Rock strata = dipping seaward
Name the types of marine transportation
Traction
Saltation
Suspension
Solution
Define traction as a process of marine transportation
Large rocks / boulders slide along the seabed in high energy locations due to the movement of the water.
Define saltation as a process of marine transportation
Small stones bounce along the seabed / beach in high energy locations, dislodging other stones
Define suspension as a process of marine transportation
Very small particles of sand / silt are picked up by and carried in the water -> murky appearance
Define solution as a process of marine transportation
Dissolved materials are transported within the mass of moving water
Which methods of marine transportation contribute to longshore drift?
All of them
Traction, saltation, suspension, solution
Define longshore drift
The movement of sediment along the coastline in a zigzag motion.
Prevailing winds cause waves to approach the coast at an angle.
The waves draw back out to sea at a right angle to the shore due to gravity -> zigzag
When does marine deposition occur?
At times of low energy
-> due to decrease in velocity / lower volume of water.
When there are low energy waves and an abundance of material produced by rapid coastal erosion.
Give the situations when deposition is likely to occur
- When sand / shingle accumulate faster than they are removed.
- As waves slow, following breaking.
- As water pauses at the top of the swash, before backwash begins.
- When water percolates into beach material as backwash carries in down the beach.
Define aeolian processes
The entrainment, transportation and deposition of sediment by wind
What causes air to move (wind)?
Air moves in response to small pressure differentials caused by the warmer land and cooler sea
What condition allows sediment to be entrained by wind?
Large tidal range -> large area of beach exposed during low tide.
What size sediment is thought to form the most significant depositional features?
Sand-sized sediment
Name the ways that sand is transported by wind
Surface creep
Saltation
Define surface creep
Where wind rolls sand along the floor
- > lower wind speed
- > more moist sand
Define saltation
Where wind temporarily lifts sand grains into the air flow
- > heights 1m
- > distances of 20/30m
- > higher wind speed
- > drier sand
Define sub-aerial weathering
Processes that slowly break down the coastline, weaken the underlying rocks or allow sudden movements / erosion to happen more easily.
In what state is material broken down in sub-aerial weathering?
In situ (stationary)
Name the categories of sub-aerial weathering
Mechanical / physical weathering
Biological weathering
Chemical weathering
What does mechanical / physical weathering depend on?
Climate eg freeze thaw
Define biological weathering
The break down of rock due to vegetation / organisms
Eg piddock shellfish - drill holes into rock
Seaweed - sways and breaks rock
Nesting birds
Where does chemical weathering occur?
Where rocks are exposed to air and moisture -> chemical processes can break down the rock
Eg solution
Name the types of chemical weathering
Oxidation Hydration Hydrolysis Carbonation Acid rain
Define oxidation (chemical weathering)
Causes rocks to disintegrate when oxygen dissolved in water reacts with some rock minerals to form oxides / hydroxides
Define hydration (chemical weathering)
The physical addition of water to rock minerals -> rock expands -> creates stress -> rock may disintegrate.
Can weaken rock and create cracks / joints.
Define hydrolysis (chemical weathering)
Mildly acidic water reacts / combines with minerals in the rock -> creates clays / dissolvable salts -> weakens rock
Define carbonation (chemical weathering)
CO2 in the rain makes carbonic acids that react with CaCO3 in limestone and chalk -> produce calcium bicarbonate = easier to dissolve
Define acid rain (chemical weathering)
Weak acids in rainwater (eg nitrogen oxides / sulphur dioxides) react with rocks (esp limestone) -> neutralisation -> erosion
Where is mass movement common?
Steep coastlines
Define mass movement
Generally either rapid sudden failure of the slope, or the effects of processes that develop over some time
What does the nature of mass movement depend on?
Level of cohesion within the sediment
Height / angle of slope
Grain size within the sediment
Temperature / level of saturation
Name the types of mass movement
Landslides Rockfalls Mudflows Rotational slip / slumping Soil creep Run-off
What are landslides? (Mass movement)
Occur on cliffs made of softer rock / deposited material -> slip as a result of failure within it when lubricated eg after heavy rainfall.
What is rock fall? (Mass movement)
Occur from cliffs undercut by the sea / on slopes affected by mechanical weathering eg frost action.
What are mudflows?(Mass movement)
Heavy rain saturated soil and surface layers become so fluid they flow downhill.
What is rotational slip / slumping? (Mass movement)
Where softer material overlies more resistant material.
Excessive lubrication -> whole panels of the cliff may slump down.
What is soil creep? (Mass movement)
Where there is am extremely slow but continuous movement of soil particles downhill.
What is run-off? (Mass movement)
Bodies of water that carry sediment, assisting in the other mass movement processes.
Eg streams, rivers etc.
Define global ocean conveyorbelt
A constantly moving system of deep-ocean circulation driven by temperature and salinity
Define salinity
Amount of salt in the water
What causes the global ocean conveyorbelt?
Thermohaline currents in deep ocean.
Wind-driven currents on surface.
How are the deep ocean currents that drive the global ocean conveyor belt created?
Water gets very cold in earth’s polar regions -> sea ice -> salty water (salt isn’t in ice) -> water is more dense -> sinks -> surface water is pulled in to replace the sinking water -> convection -> deep ocean current
How does the global ocean conveyor belt link to coasts?
The temperature of the water changes when it enters areas closer to coastlines
Define upwelling
A process in which deep, cold water rises towards the surface
How does upwelling occur?
Winds blow across the ocean surface -> push surface water away -> water rises from beneath the surface to replace this water
Where does upwelling occur?
In the open ocean.
Along coastlines.
Why does water in areas of upwelling tend to have high biological productivity?
Water that has risen from upwelling is typically colder and rich in nutrients -> fertilise surface waters.
-> good fishing grounds
Define current
Describes the movement of a body of water from one location to another
What are ocean currents driven by?
Wind
Water density differences
Tides
How do tides affect currents?
Tidal currents are strongest near the shore, in bays, in estuaries.
Tidal currents change in very regular patterns -> can be predicted.
Can travel at speeds of 8 knots or more.
Where does wind create currents?
Winds drive currents that are on / near the ocean surface.
How does wind affect currents on a localised scale?
Localised scale = near coastal areas -> upwelling
How does wind affect currents on a global scale?
Global scale = in open ocean -> currents that circulate for thousands of miles throughout ocean basins.
How does thermohaline circulation create currents?
Process driven by density differences in water due to temperature and salinity variations in parts of the ocean.
Currents occur at both deep and shallow ocean levels -> move much slower than tidal / surface (wind) currents.
How do currents affect the earth’s climate?
Currents drive warm water from the equator and cold water from poles around the earth.
Eg warm Gulf Stream brings milder winter weather to Bergen, Norway than to New York which is much further south.
Name different types of currents
Rip current
Longshore current
Flood and ebb currents
What are rip currents?
Powerful, narrow channels of fast moving water.
Can move at speeds of up to 8 feet per second.
Flow away from the shoreline towards the sea.
What are longshore currents?
A current that runs parallel to the shoreline.
It is generated by a burst of energy released from a wave as it reaches a beach / shoreline.
What are longshore currents affected by?
The velocity and angle of waves.
Wave breaks at acute angle / encounters steeper beach slope / high wave -> higher velocity longshore current.
What is a flood current?
Incoming tidal flow
What is an ebb current?
An outgoing tidal flow
Define tidal slack
The period between flood and ebb tides when there is little / no current
Define tide
Very long period waves that move through the oceans in response to the forces from the moon and sun
What are tides caused by?
Gravitational pull of the moon and sun
Define high tide?
When the crest of the wave reaches the shore
Define low tide
When the trough of the wave reaches the shore
Define tidal range
The difference in height between the high tide and the low tide
Name the types of tides
Spring tide
Neap tide
When do spring tides occur?
How often does this occur?
During full / new moons - when the earth, sun and moon are nearly in alignment.
Occurs twice each month.
How does spring tides affect the tidal range? Why?
Average tidal ranges are slightly larger.
Sun and moon are in alignment -> effect of both their gravitational pull
Why are tides more extreme during spring tides?
Sun and moon are in alignment -> effect of both their gravitational pull
When do neap tides occur?
How often?
When the sun and moon are at right angles to each other.
Twice each month.
How do neap tides affect the tidal range? Why?
Decrease the tidal range.
Moon and sun are at right angles -> cancel each other out
What are the differences between currents and tides?
Currents move left and right, tides move up and down.
Currents occur due to tides, winds and thermohaline circulation.
Tides occur due to gravitation forces of the moon and sun.
Name the factors that influence the regular patterns of tides
Morphology of seabed
Proximity to landmass
Coriolis force
What is tidal range significant for?
For shipping routes.
Coastal erosion.
Leisure reasons.
When do tidal surges occur?
Occur at times of intense low pressure (a depression).
What do tidal surges cause?
Produces very high sea levels and violent storms
