Plate Tectonics, Weathering & Slope Processes – AS-Level Review

83 question-and-answer flashcards summarising key AS-level concepts in rocks, weathering, plate tectonics and slope processes.

What are the three major rock groups?

Igneous, sedimentary, and metamorphic rocks.

Give two examples of igneous rocks.

Granite and basalt.

How are sedimentary rocks formed?

By the accumulation, compaction and cementation of sediments.

Which processes create metamorphic rocks?

Alteration of existing rocks by high pressure and/or temperature.

Define mechanical weathering.

Physical breakdown of rock without chemical change (e.g., freeze-thaw, abrasion).

Define chemical weathering.

Decomposition of rock through chemical reactions such as hydrolysis or oxidation.

Define biological weathering.

Breakdown of rock by living organisms (e.g., root growth, lichen).

List four factors that influence the rate of weathering.

Climate, rock type, topography, and vegetation.

What is exfoliation?

Peeling of outer rock layers due to temperature fluctuations or pressure release.

Describe granular disintegration.

Break-up of rock into individual mineral grains, often under thermal stress.

What is plate tectonics?

Theory describing movement of rigid lithospheric plates over the asthenosphere.

What drives plate motion?

Convection currents generated by heat from Earth’s interior.

Name the three basic plate boundaries.

Divergent, convergent, and transform boundaries.

Give one surface feature created at divergent boundaries.

Mid-ocean ridge (or continental rift valley).

What happens at a subduction zone?

One plate is forced beneath another, generating trenches, volcanic arcs and earthquakes.

Which boundary type produces the San Andreas Fault?

Transform plate boundary.

State two pieces of evidence for seafloor spreading.

Symmetrical magnetic stripes and increasing age of ocean crust away from ridges.

Why do continents appear to ‘fit’ together?

They were once joined (continental drift) before plate movement separated them.

Differentiate oceanic and continental plates in terms of thickness and density.

Oceanic plates are thinner and denser; continental plates are thicker and less dense.

What is seafloor spreading?

Creation of new oceanic crust at mid-ocean ridges as magma rises and solidifies.

Name the deepest known trench.

Mariana Trench.

Define a volcanic island arc.

Chain of volcanic islands formed above a subduction zone.

Which fold is upward-arching?

Anticline.

What causes fold mountain building?

Compression during the convergence/collision of lithospheric plates.

Give two examples of fold mountain ranges.

Himalayas and Andes (or Rockies).

Describe the freeze-thaw process.

Water enters cracks, freezes and expands, widening the rock and causing fragmentation.

What is thermal expansion weathering?

Rock expansion and contraction due to temperature change, leading to cracking.

Explain abrasion.

Rock surfaces are worn by particles carried by wind, water or ice.

What is dilatation (pressure release)?

Expansion and fracturing of rock after overburden removal lowers confining pressure.

Outline salt crystal growth.

Evaporation of saline water leaves salt crystals that exert pressure in pores and cracks.

How do plant roots weather rock?

Roots grow into joints, expand, and pry rock apart (root wedging).

Define hydrolysis in weathering.

Chemical reaction between water and minerals (e.g., feldspar to clay).

What is oxidation weathering?

Reaction of oxygen with minerals (often iron-rich) forming oxides and weakening rock.

Describe carbonation.

Carbonic acid reacts with calcium carbonate, dissolving limestone and forming karst.

State two climatic conditions that maximize chemical weathering.

Warm temperatures and high humidity.

What does a Peltier diagram illustrate?

Relationship among temperature, humidity, and chemical weathering rate; highlights optimum zone.

List four slope processes.

Weathering, erosion, deposition, and mass movement.

Define mass movement.

Downslope movement of soil or rock under gravity, independent of running water.

Differentiate slides and flows.

Slides move largely intact along a plane; flows behave like viscous fluid with internal deformation.

What is creep (in mass movement)?

Very slow, imperceptible downslope movement of soil or regolith.

Name three triggers for landslides.

Heavy rainfall, earthquakes, and human excavation (or slope loading).

Explain sheetwash.

Thin, unchannelled flow of water over a slope transporting fine sediment.

How do rills form?

Concentration of sheetwash into small channels that incise V-shaped grooves.

Define rainsplash.

Impact of raindrops dislodging soil particles, initiating erosion.

What is surface runoff?

Excess water flowing over land when rainfall exceeds infiltration capacity.

List two human activities that decrease slope stability.

Deforestation and construction on steep slopes (others: mining, over-extraction of groundwater).

Give two measures that increase slope stability.

Reforestation and installation of drainage systems (others: soil reinforcement, grading).

What is pinning in slope management?

Insertion of anchors or nails into a slope to hold rock/soil in place.

Describe netting as a slope stabilisation method.

Mesh fixed over a slope to catch falling debris or rocks.

How does afforestation aid slope stability?

Root systems increase soil cohesion and canopy intercepts rainfall, reducing erosion.

Why can poorly designed drainage fail?

It may not sufficiently lower pore-water pressure, leaving the slope saturated and unstable.

Identify one limitation to landslide prevention.

Complex geology makes failures hard to predict (others: climate change, limited funds).

What is heave in mass movement?

Upward or outward movement of soil due to freeze-thaw or wetting-drying cycles.

Contrast debris flow and mudflow.

Debris flow has coarser material; mudflow is dominated by fine sediment and water.

Which mass-movement stage directly precedes sliding?

Failure stage (after pre-failure).

What are throughflows?

Lateral movement of water within the soil, emerging lower on the slope.

State two effects of ocean ridges.

Creation of new crust and seafloor spreading (also volcanic activity, hydrothermal vents).

List three characteristic features of ocean trenches.

Extreme depth, steep sides, and narrow width.

Why are volcanic island arcs earthquake-prone?

They lie above subduction zones where slab movement generates seismic activity.

Name two mineral resources associated with seafloor spreading.

Copper and zinc (also polymetallic sulphides).

How does oxidation appear visually on rocks?

Formation of reddish or brown iron-oxide coating (rust).

What is hydration weathering?

Incorporation of water molecules into mineral structure causing expansion and weakening.

Give an example mineral formed by hydration.

Gypsum from hydration of anhydrite.

Which weathering process dominates deserts?

Mechanical (thermal expansion, salt crystal growth) due to arid climate.

Define slope angle’s role in erosion.

Steeper slopes increase gravitational force, accelerating erosion and mass movement risk.

What is a Benioff zone?

Inclined zone of earthquake foci along a subducting plate.

How do magnetic stripes support plate tectonics?

Symmetric patterns record geomagnetic reversals as crust forms at ridges and moves away.

Identify two main products of subduction.

Deep-sea trenches and volcanic arcs (plus earthquakes, metamorphism).

Why are transform boundaries generally volcano-free?

No significant mantle melting because plates slide laterally without subduction or spreading.

Explain the term ‘continental rift’.

Divergent boundary where a continent is splitting, forming rift valleys (e.g., East African Rift).

What are talus slopes?

Accumulations of rock fragments at the base of cliffs, often produced by freeze-thaw.

State one economic benefit of fold mountains.

Mineral deposits such as copper or gold become accessible through uplift.

Which two variables form a Peltier diagram’s axes?

Temperature (x-axis) and humidity (y-axis).

How does wind contribute to mechanical weathering?

Carries sand that abrades rock surfaces (aeolian abrasion).

Define ‘jointing’ in rocks.

Natural fractures that can widen during pressure release or weathering.

What effect does vegetation have on sheetwash?

Canopy intercepts rainfall and roots increase infiltration, reducing sheetwash volume.

Give an example of partially effective slope stabilisation.

Rock netting may stop small falls but not prevent deep-seated slides.

Why can climate change raise landslide risk?

Increases frequency/intensity of heavy rainfall and alters freeze-thaw patterns.

What is creep evidence on gentle slopes?

Tilted fence posts or bent tree trunks downslope.

Which plate underlies most of the Pacific Ocean?

Pacific Plate.

What distinguishes the Mid-Atlantic Ridge?

Divergent boundary between North American and Eurasian (and African) plates.

Describe mudflow composition.

High water content carrying fine sediments, flowing like wet cement.

State the three stages of fold mountain formation.

Convergence, compression & folding, uplift into mountain range.

Which chemical weathering process dominates limestone regions?

Carbonation.

How does slope benching work?

Creates step-like terraces, reducing slope angle and interrupting downslope movement.

Name two key contours on a Peltier diagram.

Lines of equal chemical weathering rate (isoweathering lines).

Why does joint spacing affect freeze-thaw?

Wider joints hold more water, amplifying frost wedging effects.

What is a monocline?

Single gentle fold where rock layers dip in one direction then level out.

Define ‘runoff threshold’.

Rainfall intensity or duration above which infiltration is exceeded and surface flow begins.

How can over-extraction of groundwater destabilise slopes?

Lowers pore-water pressure equilibrium, causing subsidence or soil contraction.

Which rock mineral is most susceptible to oxidation?

Iron-rich minerals like pyrite or magnetite.

What is the optimum climatic zone for chemical weathering?

Warm (≈20-30 °C) and humid conditions.

Explain geotextiles.

Synthetic fabrics placed in soil to reinforce and filter, enhancing slope stability.

How does sheet erosion differ from rill erosion?

Sheet erosion is unchannelled, uniform removal; rill erosion is channelled removal along small grooves.

Why are landslides common after heavy rain?

Water increases weight and pore-pressure, reducing shear strength of slope materials.

List two partially effective landslide controls and their weaknesses.

Grading may not stabilise deep failures; netting may catch debris but not stop slide initiation.

What is ‘through-flow line’ evidence on hillslopes?

Soil pipes or seepage lines where subsurface water exits, often marked by vegetation change.

Define ‘karst’.

Landscape formed by dissolution of carbonate rocks, featuring sinkholes, caves and disappearing streams.

Which mass movement term describes rapid rock detachment from cliffs?

Rockfall.

How do convection currents form in the mantle?

Heat from core causes hot, less-dense mantle to rise and cool, sinking as it becomes denser.