Geomorphic processes Flashcards
What is a coastal landscape
a stretch of coastline which may include a variety of coastal landforms
what is a coastal landform
A natural feature of a coastal landscapes stretch that has been created or shaped by Geomorphic processes
What is geomorphology
The study of landform as and the processes that create and change them
What is a Geomorphic process
physical processes such as weathering, mass movement, wave & fluvial & aeolian erosion, transportation and deposition - all of which shape coastal landforms
What are sub - aerial processes
land-based processes which alter the shape of the coastline, such as weathering and mass movement
What is an example of a coastal landscape
sediment sub cell 3a in North Norfolk
What coastal landforms does sediment sub cell 3a have??
cliffs, mudflats, spits, salt marshes, sandy beaches, shingle beaches, sand dunes and shore platforms
What 3 landscapers are formed by the littoral zone
1 - rocky cliffed coastline
2 - Sandy coastline
3 - Estuarine coastline
What are some features of a rocky cliffed coastline
- areas of high relief
- areas with resistant geology & high energy environments with more erosion than deposition
- destructive waves
What are some features of a sandy coastline
- areas of low relief with sand dunes & beaches
- areas with less resistant geology & low energy environments with more deposition than erosion
- constructive waves
What are some features of an Estuarine coastline
- areas with low relief and mudflats & salt marshes (estuaries)
- form in river mouths with less resistant rock & low energy environments a with more deposition than erosion
What are 2 main sub aerial processes
- weathering
- mass movement
What is weathering
weathering refers to the in situ deterioration of rocks, soils and minerals by chemical, mechanical or biological processes
What does in situ mean
in place - weathering doesn’t remove the rock from its location, it just weakens or breaks it down
What is mechanical weathering also called
Physical weathering
What is mechanical/ physical weathering
breaking down rocks into smaller fragments
What does smaller rocks help with
Weathering as there is an increased SA
- however temperature is moderated by the sea so some processes may not be as effective
What are the 4 main methods of mechanical / physical weathering
1 - freeze thaw
2 - pressure release
3 - thermal expansion
4 - salt crystalisation
explain freeze thaw weathering
water enters cracks/joints in rocks and expands (nearly 10%) when it freezes - excreting pressure on rock and causing it to split or for pieces to break off
Explain pressure release
when overlying rocks are removed, the underlying rock is exposed (dilatation) and expands and fractures parallel to the surface
Explain thermal expansion / insolation weathering
rocks expand when heated and contract when cooled - this can cause layers to crack and flake off
Explain salt crystalisation
solutions of salt seep into the pore spaces and then precipitate, forming crystals, this causes stress in the rock and can make them disintergrate
What is chemical weathering
when rock is decayed via chemical reactions between moisture and minerals in the rock
What chemical reaction is more effective in low temperatures
carbonation - as CO2 is more soluble in cold water
What does a 10 degrees C increase lead to for chemical weathering
A 2.5 x increase in the rate of chemical reactions
What are the 5 main chemical weatherings
1 - oxidation
2 - carbonation
3 - solution
4 - hydrolysis
5 - hydration
Explain oxidation
minerals in rock react with O2 in air or water, it becomes soluble and the original structure is destroyed
Explain carbonation
rainwater combines with dissolved CO2 to produce a weak carbonic acid - reacts with calcium carbonate in rocks
Explain solution
Any process by which a mineral dissolves in water is known as solution
Explain hydrolysis
a chemical reaction between rock minerals and water, silicates combine with water to form clays
Explain hydration
water molecules are added to rock minerals to create new minerals of a larger volume, causes flaking in rocks as some expand by 0.5% during the chemical change
How does pollution affect chemical weathering
pollution makes water more acidic, rainfall can be more acidic, chemical weathering is stronger.
What is biological weathering
the process by which plants, animals and microbes break down and weaken rocks
What are the two main biological weatherings
1 - tree root action
2 - chelation
Explain tree root action
Tree roots grow into cracks or joints in rocks and exert outward pressure, falling trees can cause the roots to bring soil and rocks bringing them to the surface
Explain chelation
Chelates are organic acids from decomposition, they cause water to become acidic and react with some minerals e.g. molluscs can secrete acids that make hollows in rocks
What is mass movement
the down-slope transport of material (occurs when forces acting on cliff exceed forces holding rocks together
What are the two causes of slope failure
- reduction in internal resistance of a slope
- increase in stress - forces acting on a slope
What are the 4 mass movements
1 - rockfall
2 - mudflows
3 - landslides
4 - landslips / slumps
Explain rockfall
- the sudden collapse or breaking away of individual rock fragments at a cliff face
- usually steep / vertical cliffs with resistant rock which is heavily jointed
- often triggered by mechanical weathering
- once broken away it is talus or scree
Explain mudflows
- earth and mud flowing downhill
- usually over weak bedrock such as clay
- often after heavy rain
- water gets trapped in rock, increasing pore water pressure, leading to slope failure
- sudden and fast flowing
Explain landslides
- a block of rock moving rapidly downhill along a slide plane
- often triggered by heavy rainfall, as friction on slip surface is reduced
- can occur over matter of seconds
Explain landslips / slumps
- the slide surface is curved
- usually in weak / unconsolidated clays and sands
- often when permeable rock overlies impermeable rock, causing a build up in pore pressure
- have sharp break of slope and formation of scarp
How can waves shape landforms
Waves have significant energy so when they break onshore, the energy can be expended through Geomorphic processes to shape landforms
What are the 5 types of wave erosion
1 - attrition
2 - pounding
3 - abrasion / corrasion
4 - solution / corrosion
5 - hydraulic action
Explain attrition
when rocks collide with each other and progressively become worn away until they are smooth & more rounded, eventually forming sand
Explain pounding
when the mass of a breaking wave exerts pressure on a rock causing it to weaken (can reach 30 tonnes per/m**2)
Explain abrasion / corrasion
when waves armed with rock particles scour the coastline
Explain solution / corrosion
dissolving minerals like calcium carbonate, only important if the rocks contain these minerals
Explain hydraulic action
waves break against a cliff face, air and water trapped in cracks become compressed, waves recede the pressure is released and water expands widening the crack (average pressure is 11,000 kg/m**2)
What is fluvial erosion
erosion in a coastal environment such as a river mouth
What are the 3 stages of fluvial erosions
1 - erosion
2 - transportation
3 - deposition
Explain erosion
fluvial erosion of rivers is thee main source of a rivers sediment load
Explain transportation
sediment is then transported along the river’s course (traction, suspension, saltation and solution)
Explain deposition
as rivers enter the sea there is a reduction in their velocity as the flowing water in the channel enters the static body of seawater, less energy leads to deposition
Largest particles are deposited first, the finest are carried out further to sea
Flocculations may occur
What is flocculation
The mixing of fresh and salt water means clay particles clump together due to electrical charges between them in salt solutions, they become heavier and sink to the seabed
What does flocculation lead to the formation of
mudflats or deltas
How much are coastal landscapes affected by aeolian erosion
Significantly influenced as there is a lot of exposure so winds can influence the landscape a lot
What is deflation
when the wind moves up sand particles and moves them
How high will winds of 40kph lift sand
only 1m so this erosion only occurs at the base of cliffs
What happens to the erosive force as wind velocity increases
it increases exponentially
What type of sand is easier for the wind to pick up
Dry sand is easier to pick up than wet sand
Aeolian forces can move particles up to what size
2mm - the largest will only move by a surface creep
When will particles be deposited when affected by Aeolian forces
when the wind speed falls, usually due to surface friction
What moves material in a coastal system
waves, tides and currents (all methods of transportation)
What are the 4 methods of transportation of particles
1 - solution
2 - suspension
3 - saltation
4 - traction
Explain solution
minerals dissolved into the mass of moving water, remain in solution until water is evaporated and they precipitate out of the solution
Explain suspension
small particles of sand, silt and clay can be carried by currents ( gives brown appearance in sea water)
Explain saltation
A series of irregular movements of material which is too heavy to be carried continuously in suspension
Explain traction
the largest particles in the land may be pushed along the sea floor (seldom continuous)
Once deposited onshore what can move the sediment
longshore drift
Explain longshore drift
- When waves have broken, the swash Carries particles diagonally up the beach (direction of prevailing wind) then gravity causes backwash to move them back down the beach
- overtime this causes material to
be moved along the beach, as they move the particles become smaller & more rounded
When is material deposited
when there is a loss of energy caused by a decrease in velocity and/or volume of water
When does deposition tend to take place in coastal systems
- where rate of sediment accumulation exceeds removal
- when waves slow down immediately after breaking
- at the top of the swash, the water is no longer moving for a brief moment
- during backwash when water percolates into the beach material
- in low energy, sheltered environments
what is settling velocity
The velocity at which sediment particles are deposited
The larger and heavier the particles are how much energy is required to move them
a lot of energy is required to move them
What happens when flow velocity decreases
the largest particles are deposited first and the finest particles are deposited last
