physical rocks and weathering case studies

AS geography

example of gabions

tongariro crossing

example of soil nailing

malaysia after the 2022 landslides

example of netting

kaikoura's rockfall canopy

example of grouting

indonesia after the landslides in semarang

example of afforestation

muriwai beach

example of drainage and grading

fox drainage company in auckland

example of an urban heat island

western sydney

example of quarrying/excavation and surface loading

the aberfan disaster in 1966, buried a junior school, killed 144 people, caused by a spoil tip that was started in 1958 and reached 34 metres, three weeks of heavy rain saturated the tip which contained waste material from coal mining

malaysia 2022 landslides

1st of january, 6 landslides in selangor, 16th of december batang kali landslide trapped 91 people at a farmers' campsite and killed 32

factors that contributed to the malaysia 2022 landslides

undercutting of slopes to build roads, removal of vegetation for construction, a heavy monsoon season from may to september, high clay content in slopes, 25% of malaysia being rocks and hills

amelioration in malaysia after the 2022 landslides

soil nailing aka pinning to increase shear strength of soil, straw wattles at the bottom of slopes, coir rolls which cover roots and facilitate plant growth, bamboo fascines which minimises soil movement, afforestation to decrease chemical weathering and overland flow

money stats for the malaysia landslides case study

economic loss of up to 1 billion USD due to landslides between 1973 and 2007, after the 2022 landslides, 540 million ringgit spent on landslide risk mitigation projects, in 2025, 600 million ringgit allocated to tackle flash floods and landslides

examples of humans mismanaging the environment and decreasing slope stability

undercutting, deforestation, quarrying/excavating, surface loading, mining, increasing co2 emissions, having urban heat islands

examples of humans managing the environment and increasing slope stability

terracing, grading, gabions, grouting, afforestation, pinning, netting, soil nailing, coir rolls, straw wattles, bamboo fascines

name the parts of a slope

crest, cliff, talus, pediment

characteristics of the crest a slope

where weathered material falls off a cliff and where soil creep occurs

characteristics of the cliff of a slope

vertical area where bare rock juts out and rock falls occur

characteristics of the talus of a slope

where boulders and rocks from a collapsed cliff collect (these deposits have the same name as the part of the slope)

characteristics of the pediment of a slope

foot of the slope and is covered with sediment known as scree that comes from the talus of a slope

what is regolith?

the layer of unconsolidated soil and rock that covers bedrock (literally means 'rock blanket')

slopes are an open system, what are examples of inputs?

energy from the sun, precipitation, wind, material from weathering

slopes are an open system, what are examples of outputs?

re-radiated heat from the sun (re-emitted from the ground as infrared radiation aka longwave radiation), runoff water, sediment from the regolith

examples of endogenic factors affecting slope stability

rock type and structure: porosity and permeability (larger grain = easily weathered), chemical make up of rocks (contains limestone or chalk or is it quartz?), deepness of regolith (deep regolith means an unstable slope)

examples of exogenic factors affecting slope stability

climate: temperature and rainfall (what type of weathering is happening?), aspect (in nz, northern slopes = warmer, southern slopes = colder and more freeze thaw), vegetation (intercepts water and roots increase shear strength)

what are the types of mass movement?

heaves/creeps, flows, slides/slumps, falls

example of a heave/creep

in the uk, soil creep happens at a rate of 1-3mm per year while in tropical rainforests, the rate can be up to 10mm a year

example of a flow

1985 armero tragedy in columbia, eruption of nevado del ruiz led to a lahar (volcanic mudflow) that killed 25k people

example of a slide/slump

140k landslides caused by cyclone gabrielle in nz (2023), the batang kali landslide in malaysia (2022)

example of a fall

kaikoura in nz (especially on state highway 1 with the rockfall canopy), furnas lake in brazil (jan 2022)

when does slope failure occur?

when there is either a decrease in shear strength, an increase in shear stress, or a combination of both

what is shear strength

the resistance of a slope against shear stress and the material's ability to stay together based on particle friction and cohesion

what is shear stress

the force of gravity that pushes downslope and causes material to slide

smaller scale mass movements (mini mass movements)

rainsplash, surface run-off/overland flow (which causes rilling and sheetwash)

what is rainsplash (3 parts)

detachment: drops of rain cause particles of soil to detach and bounce, transport: they bounce downslope, deposition: material collects at the bottom of the slope

two types of surface run-off/overland flow?

hortonian flow where water doesn't infiltrate into the ground because it cannot absorb it fast enough, and saturation flow where the soil's capacity has been reached preventing further infiltration

what is rilling/rill erosion

rill erosion occurs when water from surface run-off/overland flow forms channels in the ground that concentrates water into narrower flow paths

where does rilling/rill erosion occur?

on steeper slopes

what is sheetwash erosion?

surface debris is removed and productive top soil on the slope is lost

where does sheetwash erosion occur?

on gentler slopes

peltier's diagram (louis peltier, 1950)

the peltier diagram predicts the type of weathering that will occur in a region based on the mean annual rainfall and temperature recorded there

what are the three types of chemical weathering?

carbonation, hydrolysis, hydration

example and explanation of carbonation

waitomo caves in nz (rocks that contain calcium carbonate in them such as limestone or chalk are broken down by acid rain created when co2 and water form a weak carbonic acid. carbonic acid in the rain reacts with calcium carbonate in the rocks to create calcium bicarbonate which is soluble and gets washed away by rain)

example and explanation of hydrolysis

skull rock at joshua tree national park in california (rocks containing a mineral called feldspar such as granite react with acid rain and create kaolin clay, potassium hydroxyl and silicic acid. the latter two are washed away leaving kaolin to create a smooth surface on rocks)

example and explanation of hydration

river floors and seabeds all over the world (anhydrite and gypsum are minerals commonly found in mudstones and shales all over the world. these minerals absorb water and the volume of the rocks can expand up to 1600%. this causes the rocks to crack and breakdown as pressure grows)

what are the five types of mechanical weathering?

freeze thaw, exfoliation (onion-skin weathering), salt crystallisation, dilatation (pressure release), vegetation root action (biological weathering)

example and explanation of freeze thaw

snowdonia in wales (water gets into the cracks of rocks and expands by 10% when it freezes causing the cracks to widen. when the ice melts, more water is able to infiltrate into the crack so that when it freezes again, the cracks widen even more and eventually the rocks break)

example and explanation of exfoliation (onion-skin weathering)

sugar loaf mountain in rio de janeiro or the sonoran desert in california (occurs in places with there is a large diurnal temperature range. during the day, rocks warm up but the outer layers are hotter and expand more than the inner layers. when temperatures drop at night, the outer layers cool and contract while the inner layers still retain some heat. the constant pressure and pressure release causes layers of rock to detach)

example and explanation of salt crystallisation

the dead sea in jordan (salt water gets into the joints of rocks and once the water evaporates, the sodium can expand up to 300% when temperatures are between 26-28 degrees celsius. this exerts pressure on rocks and the joints disintegrate. porous rocks are most susceptible)

example and explanation of dilatation (pressure release)

cairngorms in scotland (as overlying rocks are removed by erosion, underlying rocks expand due to pressure release. this causes cracking and sheets of rock break off)

example and explanation of vegetation root action (biological weathering)

rainforests on yakushima island in japan (roots exert pressure on rocks causing them to weaken or disintegrate. they can also penetrate rocks, creating cracks and breaking them. decaying vegetation releases organic compounds that react with rocks and are an example of chemical weathering)

van't hoff's law

states that the rate of chemical weathering increases 2-3 times for every 10 degree celsius increase in temperature

example and explanation of karst scenery

the burren in county clare in western ireland and the waitomo caves in nz and the south china karst which is a unesco world heritage site (landscape that is created when limestone weathers. can be a pavement with clints and grikes, an underground cave system, or above ground cliffs)

factors affecting the type and rate of weathering that occurs

climate, rock type, rock structure, vegetation, relief, aspect

how climate affects the type and rate of weathering

as seen in peltier's diagram and van't hoff's law, the amount of rain and the temperature in a region determines the type of weathering that will occur. in warmer and wetter areas, chemical weathering is more likely to occur while in colder and dry areas, mechanical weathering is more likely to occur

how rock type affects the type and rate of weathering

the chemical make up of a rock can affect the type and rate of weathering that it experiences. rocks like limestone or chalk that contain calcium carbonate will experience carbonation while rocks like granite that contain feldspar will experience hydrolysis and rocks like mudstones and shales that contain anhydrite or gypsum will experience hydration. rocks like quartz are chemically resistant and cannot be weathered chemically

how rock structure affects the type and rate of weathering

the permeability and porosity of rocks can affect the type and rate of weathering that occurs. large grain rocks are more susceptible to weathering as they have a large void space and high permeability (porous and permeable) however, very fine grain rocks may also weather quickly due to increased surface area

how vegetation affects the type and rate of weathering

the roots of plants exert pressure to rock joints and can widen cracks. furthermore, organic compounds released from plants can help break rocks down and increase chemical weathering

how relief affects the type and rate of weathering

steeper slopes increase rates of physical weathering as rocks fall away to expose new rocks easily. however, chemical weathering requires rain to be stationary and steeper slopes encourage overland flow meaning chemical weathering rates are slowed

how aspect affects the type and rate of weathering

the direction a slope faces affects the type and rate of weathering it will experience. in the southern hemisphere, northern slopes are warmer than southern slopes as insolation hits them directly. this means southern slopes experience more freeze thaw while the warmer northern slopes may experience weathering such as exfoliation instead

example of a divergent (constructive) plate boundary where two continental plates diverge

east african rift valley, between the african plate, somali plate, and arabian plate that creates a y-shaped rift system

example of a divergent (constructive) plate boundary where two oceanic plates diverge

mid-atlantic ridge in iceland, seafloor spreading occurs between the eurasian plate and the north american plate

example of a convergent (destructive) plate boundary where an oceanic and continental plate converge SUBDUCTION

the andes in south america, the nazca oceanic plate subducts under the south american continental plate to create a mountain range

example of a convergent (destructive) plate boundary where two oceanic plates converge SUBDUCTION

mariana trench and the japanese island arcs, where the pacific plate and philippine sea plates converge to create a trench and the same two plates subduct under the eurasian and north american plates to form an arc of volcanic islands

example of a convergent (destructive) plate boundary where two continental plates converge COLLISION

the himalayas in nepal, the indian and eurasian plates converge at a collision bounday and form fold mountains

example of a conservative (passive) plate boundary

the san andreas fault in california, the north american and pacific plates move in the same direction creating a transform fault

lithosphere

part of the crust and the mantle and is broken into plates that move due to convection currents

asthenosphere

part of the mantle, underneath the lithosphere, and is where convection currents flow