Rocks And Weathering Flashcards
Characteristics of inner core
- Solid ball of iron/nickel
- Very hot due to pressure and radioactive decay
- Heat is responsible for Earth’s internal energy and it spreads throughout.
Characteristics of the outer core
- Semi-molten
- Iron/nickel
Describe the mantle
- Mainly solid rock - high in silicon
- Very top layer of mantle is semi-molten magma (asthenosphere). Lithosphere rests on top.
Describe the Asthenosphere
-Semi-molten layer constantly moving due to flows of heat (convection currents)
- Movements are powered by heat from core
- Lithosphere above
Describe the lithosphere
- Broken up into plates
- Majority is within mantle
- Top is the crust - land and sea
Describe the crust
- Thin top of the lithosphere
- Oceanic crust is dense and destroyed by plate movement, continental crust is less dense and not destroyed
What is the plate tectonic theory
Plates move due to the convection currents in the asthenosphere which push and pull plates in different directions. Convection currents are causes when the less dense magma rises, cools, then sinks. Edges of where plates meet = plate boundaries.
Lithosphere is broken up into large slabs of rock = tectonic plates.
Describe the process of convection currents
- Heat from inner core converts through mantle into asthenosphere
- Hot magma rises as it becomes less dense with heat (particles spread out)
- Magma is cooler at the top as it is further away from heat source. Becomes more dense and sinks back down to bottom.
- Cooler magma is reheated and begins to rise again, creating a loop called a convection current.
What are the types of plate boundaries
- Destructive/convergent
- Constructive/divergent
- Conservative
Movements at plate boundaries
- Destructive/convergent: move towards each other
- Constructive/divergent: move away from each other
- Conservative: parallel to each other
What happens at a destructive/convergent plate boundaries with continental & oceanic plates
- The denser oceanic plate subducts below the continental
- Subducting plate leaves a deep ocean trench
- Fold mountains occur when sediment is pushed up during subduction
- Oceanic crust is melted as it subducts into asthenosphere
- Extra magma created causes pressure to build up
- Pressurised magma forces through weak areas in continental plate
- Explosive, high pressure volcanoes erupt through continental plate ( composite volcanoes)
What happens at a destructive/convergent plate boundaries with oceanic & oceanic plates
- Heavier plate subducts leaving an ocean trench, fold mountains occur
- Built up pressure causes underwater volcanoes bursting through oceanic plate
- Lava cools and creates new land=island arcs
What happens at a destructive/convergent plate boundaries with continental & continental plates
- Both plates aren’t as dense as oceanic so lots of pressure builds
- Ancient oceanic crust is subducted slightly but no subduction of continental crust.
- Pile up of continental crust on top of lithosphere due to pressure between plates
- Fold mountains formed from piles of continental crust
What happens at a constructive/divergent plate boundaries with oceanic & oceanic plates
- Magma rises in between the gap left by the two plates separating, forming new land when it cools
- Less explosive underwater volcanoes formed as magma rises
- New land forming on the ocean floor by lava filling the gaps is known as sea floor spreading.
What happens at a constructive/divergent plate boundaries with continental and continental plates
- Any land in the middle of the separation is forced apart, causing a rift valley
-Volcanoes form where where magma rises - Eventually the gap will most likely fill with water and separate completely from the main island
What is salt weathering
- occurs due to salt crystal growth inside the cracks and pores in rocks
- when saline solutions (salt water) gets into cracks and evaporates, it leaves behind the salt crystals that were in the solution
- salt crystals accumulate over time, build up of pressure expands the gap in the rocks
- eventually this can cause the rocks to break off or disintegrate
What is ridge push
The slop created when plates move apart has gravity acting upon it as it as at a higher elevation. Gravity pushes the plates further away, widening the gap.
What is the heating/cooling processes (exfoliation)
- Repeated heating and cooling of rocks can cause rocks to be broken down and weathered away
- Rocks can expand rapidly when hot then contract rapid when cold causing the breaking apart of layers of rock
- e.g: deserts: changes in temperature can cause stress on the outer layers of rock. Causes the outer layers to peel off
What is slab pull
When a plate subducts, the plate sinking into the mantle pulls the rest of the plate with it, causing further subduction.
What lines can occur at a conservative plate boundary
Fault lines - ground is cracked by the movement
What is weathering
The wearing down or breaking of rocks while they are in place.
What is physical weathering
Weathering that affects rocks and rock formations
What is freeze-thaw
- Weathering due to freezing temperatures
- Water gets into cracks of rocks, freezes and expands
- Repeated action puts pressure onto rock eventually causing it to shatter and break off
What is pressure release (dilation)
- a type of weathering caused when rocks that are under a great amount of pressure no longer have to bear a heavy load causing expansion and fracturing
- when there is removal of weight, underlying rocks expand when pressure is released, thus causing fractures to form on rock surface
- e.g when rocks from beneath earths surface under tremendous pressure, and when load above is eroded away, pressure s removed and rock expands
What is vegetation root action
- when vegetation grows (plants/trees) their roots too grow so need more space
- growing roots exert pressure onto the surrounding rock, eventually causing rocks to break apart
What is chemical weathering
The breaking dawn of rocks caused by chemical reactions
What are 4 components of chemical weathering
- hydrolysis
- hydration
- carbonation
- oxidation
What is hydrolysis weathering
The breaking down of rock when it reacts with water. Rocks can break down when they are soluble in water e.g chalk.
What is hydration
Occurs when water is absorbed into a substance causing a new substance to form. Hydration causes rocks to expand in size and volume when can make them susceptible to other forms of weathering.
What is carbonation
When co2 is dissolved in water (carbonic acid) reacts with rocks and breaks them down.
Factors affecting weathering
- climate
- rock type and structure
- vegetation
- relief
How does climate affect weathering
- temperature and precipitation
- some climates accelerate certain types of weathering whereas others make it impossible to occur
- alpine climates: temperatures fluctuate more rapidly than in polar environments, freeze-thaw is more severe
- salt crystal growth favours dry climates, allowing water to evaporate to leave salt crystals
How does rock type and structure affect weathering
- dictates the rate at which weathering will occur and what type will take place
- some rocks (water soluble) more vulnerable to chemical erosion so weathered at a quicker rate
- permeable rock types have pores which can leave so are vulnerable to many types of weathering as more energy is required to break down the rock
- rocks with natural weakness areas (layered sedimentary rocks) are also vulnerable to weathering
How does vegetation affect weathering
- type and amount
- root action weathering will be at a much higher rate in areas with high vegetation especially large trees
How does relief affect weathering
- rate and type
- areas of gentle relief likely subjected to standing water and water which infiltrates into the ground
- steep relief more common for precipitation to fall as overland flow
What is the Peltier Diagram
illustrates the relationship between temperature and rainfall and the different weathering types that prevail.
What are the 3 processes that can occur on slopes and affect them
- erosion & weathering: change landscape
- movement of water and sediment down a slope
- mass movement of material: takes place in variety of forms
What is water and sediment movement
Due to the effect of gravity on slopes, water and sediment moves downhill
What is mass movement
the large scale movement of materials on a hill slope caused when the stress exerted exceeds the internal strength of the hill slope, causing instability
What direction will mass movement always be
downhill due to force of gravity
Internal strength of slope materials (weakest to strongest)
- non-cohesive materials: coarse grains like sand
- cohesive materials: silts and clays
- rock: sandstone, slate
What are 4 types of mass movements
- heaves
- flows
- slides
- falls
Characteristics of heaves
- occur on slopes made from cohesive and non-cohesive materials
- frost heave and soil creep are examples
- slowest and most prevalent form of mass movement
Process of heaves
- occur when soil particles are pushed and due to force of gravity move downwards
- on slopes made from cohesive materials, can cause soil to ripple, creating steps - terracettes
- particles fall downwards under influence of gravity
- when occurs on slop it can create lines of stones - stone stripes
Characteristics of flows
- occur on slopes made from cohesive materials (slit/clay)
- mudflows are an example
- faster than heaves but slower than falls and slides
Formation of a flow
- controlled by moisture within the slope
- when soil becomes oversaturated the cohesive bonds within the soil break causing soil to move downhill like a viscous liquid
- often occur under heavy rainfall conditions especially rainfall that falls within short periods of time (leads to less infiltration and percolation into groundwater stores)
Characteristics of falls
- occur on slopes made from rocks
- happen very suddenly: dramatic effects
- due to strong internal strength of rocks the slopes can be very steep
- e.g rockfall
How are rockfalls triggered
- freeze-thaw processes
- seismic waves
- gravitational stress
Characteristics of slides
- landslide is an example
- rockslides are a type of landslide that occur on slopes made from rocks
- occur along faults in rock
How are landslides triggered
- seismic waves
- gravitational stress
- this movement is large scare, causing a great deal of material to be moved in a short space of time
How do humans have an impact on slope stability
- stability may decrease due to human activities
- humans may reinforce slope stability as increased slope stability reduces hazard to environment and human life
What are examples of human activities can cause a decrease in slope stability
- mining
- construction
- tourism
- agriculture
- forestry
How does mining decrease slope stability
- its frequent
- removes support from the slope either underlying or lateral support
- brings a large amount of waste which is left on the slope so adds stress resulting in mass movement processes
How does construction decrease slope stability
- stress on a hill slope: weight of housing/dams
- slopes may be undercut in order to build
- groundwater is affected due to sewage systems, drainage systems, water demand
- water erosion can affect internal strength of a slope: hydraulic engineering can cause surrounding slope to become saturated if not properly managed (mudslides & other mass movements
How does tourism affect slope stability
- alpine slopes: skiing
- creates stress on hill slopes
- erosion of slope increases due to trampling of vegetation, skis heavy machinery walking which damages and compacts the soil
- in alpine areas where seasonal melting is common, dramatic increase of water can trigger mass movement processes (mudslides) where slope has been degraded
How does agriculture decrease stability of slopes
- soil can be compacted through heavy machinery and animals leaving slopes vulnerable to soil erosion, water flows and reduced vegetation cover
- reduction of vegetation cover due to overgrazing and trampling causes degradation of soil, vegetation is vital to soils structure so landlsuides are a hazard
- increased rates of soil erosion due to less vegetation: hill slopes left exposed to elements when vegetation is removed causing erosion and weathering processed to take place
How does forestry decrease stability of slopes
- soil strength is enhanced by roots of trees so strength of hill slope is compromised
- deforestation decreases interception so more water flows over hill slope and infiltrates as well as less water being taken up by trees roots increasing saturation of soil
- clearcutting leaves slope vulnerable especially to wind
- forest roads are constructed for use of transporting timber interrupting natural flow of water as well as creating channels for run-off being highly erosive
What strategies increase the stability of slopes
- afforestation
- netting
- pinning
- grading
How does afforestation increase stability of slopes
- roots from trees increase soils internal strength so slope can take more stress before falling
- more trees reduce saturation of soil both from interception and taking up water from roots
- reduces the trigger of high soil saturation levels and decreases erosion caused by water
How does netting increase slope stability
- can be placed over a slope
- contains any falling of debris or rock beneath it
- prevents falls as there is little room for anything to fall
How can pinning increase slope stability
- soil nailing is where steel rods are drilled into the soil allowing more weight to be carried
- rock bolting is where bolts are drilled into rock slopes in a specific pattern transferring the load from the weaker exterior to the stronger interior of the slope
How does grading increase slope stability
- the process of reshaping the surface of a slope to a specified slope
- completed using heavy machinery (excavators and graders)
- purpose to to provide a more uniform topography
