Geography Topic 3 - Rocks and Weathering

CAIE Topic 3 Rocks and Weathering flashcards

What are the 7 major tectonic plates?

Pacific Plate (largest), North American Plate, South American Plate, Eurasian Plate, African Plate, Australian-Indian Plate, Antarctic Plate

What is the Ring of Fire?

The circum-Pacific belt containing ~75% of world's active volcanoes and ~90% of earthquakes. Results from active subduction around most Pacific margins.

What is the Mid-Ocean Ridge System?

The longest mountain chain on Earth (60,000km) running through all major ocean basins. Represents divergent boundaries where new oceanic crust forms.

What is the Alpine-Himalayan Belt?

Continental collision zone extending from Mediterranean through Middle East to Southeast Asia, representing continental-continental convergence creating world's highest mountain ranges.

What are the characteristics of continental crust?

35-70km thick, old (>1500 million years), light density (2.6 g/cm³), mainly granitic (rich in silica + aluminium)

What are the characteristics of oceanic crust?

6-10km thick, young (<200 million years), dense (3.0 g/cm³), mainly basaltic (rich in silica + magnesium + iron)

What is the lithosphere?

Rigid outer shell (crust + uppermost mantle), ~70km thick, brittle and fractured into plates

What is the asthenosphere?

Weak, semi-molten layer beneath lithosphere that allows plate movement

What percentage of Earth's volume does the mantle make up?

~82% of Earth's volume, largely solid but convects slowly due to internal heat

What was Wegener's Continental Drift theory (1912)?

Proposed all continents were once joined in supercontinent (Pangaea) which broke apart ~250 million years ago. Evidence included fossil and geological matches across continents.

What is sea-floor spreading (Hess, 1960s)?

Convection currents push magma up at mid-ocean ridges, creating new crust that spreads outward

What is paleomagnetism evidence (Vine & Matthews, 1963)?

Alternating bands of reversed and normal magnetism on either side of Mid-Atlantic Ridge proved symmetrical spreading

List 5 key pieces of evidence for plate tectonics

1) Jigsaw fit of South America and Africa 2) Fossils like Mesosaurus in Brazil and SW Africa 3) Matching rock sequences in Scotland and Newfoundland 4) Ancient mountain ranges linking continents 5) Permo-Carboniferous glacial deposits in Brazil and West Africa

What are convection currents?

Heat from radioactive decay in mantle drives rising and sinking currents, pushing plates apart at ridges and recycling them at trenches

What is slab pull?

The dense, cold edge of a subducting plate pulls the rest of the plate downward into the mantle

What is ridge push?

Elevated ridges push plates sideways under gravity as new crust forms

What are hotspots and mantle plumes?

Localised upwellings of magma (e.g. Hawaiian Islands) produce volcanic chains, even away from plate boundaries

What is a divergent boundary?

Zones where tectonic plates move away from each other, allowing asthenosphere material to rise and create new oceanic lithosphere. Called "constructive" because new crust is continuously formed.

Describe the process at divergent boundaries

1) Mantle convection brings hot material upward 2) Thermal expansion causes lithospheric bulging and cracking 3) Decompression melting as asthenosphere rises 4) Basaltic magma erupts through fissures 5) Sea-floor spreading pushes older crust away symmetrically

What is the Mid-Atlantic Ridge spreading rate?

~2-3cm/year (slow-spreading ridge)

What is the East Pacific Rise spreading rate?

~6-18cm/year (fast-spreading ridge)

What landforms are created at divergent boundaries?

Mid-ocean ridges (2-3km above abyssal plains), rift valleys (1-2km deep), transform faults, pillow basalts, hydrothermal vents

What is Iceland's significance?

Unique exposure of mid-ocean ridge above sea level at Mid-Atlantic Ridge

What is a conservative boundary?

Linear zones where two plates slide horizontally past each other along vertical fault planes. "Conservative" because crustal material is neither created nor destroyed.

Describe the process at transform boundaries

1) Plates move in opposite directions along strike-slip fault 2) Friction builds up as surfaces lock together 3) When stress exceeds elastic limit, sudden brittle failure occurs 4) Energy release generates shallow-focus earthquakes (0-20km deep)

What is the San Andreas Fault System?

Pacific Plate moves northwest (~3-4cm/year) relative to North American Plate. Extends 1,200km through California. Right-lateral strike-slip motion.

What major earthquakes occurred on San Andreas Fault?

1906 San Francisco (M7.9), 1989 Loma Prieta (M6.9)

What landforms are created at transform boundaries?

Linear rift valleys, pressure ridges, offset drainage patterns, sag ponds, shutter ridges, beheaded streams

What is a convergent boundary?

Zones where plates move toward each other, resulting in subduction or collision. Called "destructive" because oceanic lithosphere is consumed.

What happens at ocean-continental convergence?

Dense oceanic plate (~3.0 g/cm³) subducts beneath lighter continental plate (~2.6 g/cm³) at 30-70° angle forming Benioff-Wadati zone of earthquake activity

What is the Andes Mountains example?

Nazca Plate subducts beneath South American Plate at ~7-8cm/year. Peru-Chile Trench (8,000m deep), Andean Volcanic Arc with 49 peaks >6,000m

What happens at ocean-ocean convergence?

Older, denser oceanic plate subducts beneath younger oceanic plate, creating volcanic island arc 150-200km from trench

What is the Lesser Antilles example?

Atlantic oceanic lithosphere subducts beneath Caribbean Plate. Puerto Rico Trench (8,600m deep), volcanic islands from Grenada to Virgin Islands

What happens at continental-continental convergence?

Neither continental plate can subduct due to low density. Collision results in intense compression, folding, and crustal thickening (may exceed 70km)

What is the Himalayas example?

Indian Plate collides with Eurasian Plate (~70 million years ago). Ongoing convergence at ~5cm/year. Mount Everest (8,849m), crustal thickness >70km

What is subduction?

Process whereby one tectonic plate descends beneath another into Earth's mantle, typically when dense oceanic lithosphere encounters less dense continental lithosphere

What drives subduction?

Slab pull (gravitational force), ridge push (gravitational sliding), mantle convection, trench suction

What is the Benioff-Wadati Zone?

Inclined plane of earthquake hypocenters extending to ~680km depth, defining subducting slab geometry

What is the oceanic crust structure from top to bottom?

1) Sedimentary layer 2) Pillow basalts 3) Sheeted dikes 4) Gabbro layer

How do fold mountains form at continental collision?

1) Tethyan closure through oceanic subduction 2) Soft collision of continental margins 3) Hard collision creating main ranges 4) Ongoing convergence causing active uplift

What are the structural features of the Himalayas?

Main Himalayan Thrust, crystalline nappes (overturned rock sheets), duplex structures (repeated thrust faults), syntaxial bending

How do the Andes form differently from Himalayas?

Subduction-related: accretionary tectonics, batholith emplacement, back-arc thrusting, volcanic arc formation. Structure: coastal ranges, central volcanic arc, eastern cordillera, Altiplano plateau

What are the characteristics of mid-ocean ridges?

Linear mountain chains (60,000km total), 2-3km above abyssal plains, 1,000-4,000km width, segmented by transform faults every 30-100km

What's the difference between slow and fast-spreading ridges?

Slow (

What are ocean trenches?

Deepest ocean parts (6,000-11,000m), formed by flexural downward bending of oceanic lithosphere at subduction zones. Asymmetrical profile, linear geometry

What is the Mariana Trench?

Maximum depth: Challenger Deep (10,994m) - deepest known point. Philippine Sea Plate subducts beneath Pacific Plate

What is the Peru-Chile Trench?

Length: 5,900km, maximum depth >8,000m, Nazca Plate subduction at ~7cm/year

How do volcanic island arcs form?

1) Slab dehydration releases water 2) Mantle wedge flux melting (H₂O reduces solidus temperature) 3) Andesitic melts rise through overlying plate 4) Repeated eruptions build volcanic edifices above sea level

What is the typical arc structure?

Fore-arc (non-volcanic, 100-200km from trench), volcanic front (line of active volcanoes), back-arc (may have extension/spreading), volcanoes 50-100km apart

What is weathering?

The decomposition and disintegration of rocks in situ (in their original position). Creates irreversible changes: volume/density changes, grain size modification, surface area increases, permeability changes, strength reduction.

What are the three types of weathering?

Physical (mechanical), chemical, and biological weathering

What is physical weathering?

Mechanical breakdown of rocks into smaller fragments without changing their chemical composition. Original rock material remains chemically unchanged but physically fragmented.

What is freeze-thaw weathering?

Water enters rock cracks, freezes at 0°C expanding by ~10%, exerting enormous pressure (max 2,100 kg/cm² at -22°C, average 14 kg/cm²) on surrounding rock walls

What are optimal conditions for freeze-thaw?

Frequent temperature fluctuations around freezing point, abundant moisture, pre-existing rock weaknesses, periglacial and alpine environments

What landforms does freeze-thaw create?

Scree slopes, talus, blockfields, tors

What is salt crystal growth weathering?

Two mechanisms: 1) Thermal expansion of sodium sulphate/carbonate by 300% at 26-28°C 2) Crystallisation pressure as salt crystals form and grow in rock pores during evaporation

What are optimal conditions for salt crystallisation?

Hot desert regions with high diurnal temperature ranges, low rainfall/high evaporation, rocks with high porosity/permeability (chalk decomposes fastest), coastal areas with salt spray

What is heating and cooling weathering?

Large diurnal temperature ranges cause rocks to expand when heated and contract when cooled, creating internal stresses. Desert temperatures exceed 40°C daytime, near freezing nighttime.

What did Griggs (1936) prove about thermal weathering?

Demonstrated that moisture is essential - temperature change alone is insufficient for breakdown

What is pressure release (dilatation)?

Removal of overlying rock layers by erosion allows underlying rocks to expand and fracture parallel to surface. Creates horizontal pseudo-bedding planes and vertical joints.

What landforms does pressure release create?

Sheeting joints, exfoliation domes (Half Dome, Yosemite)

How does vegetation root action work as physical weathering?

Plant roots growing in rock cracks exert wedging pressure as they expand, gradually widening existing fractures. Tree root systems particularly effective on larger scale.

What is chemical weathering?

Decomposition of rocks through chemical reactions, creating altered rock substances with different mineral compositions. Water is key medium as reactant and transport agent.

Where is chemical weathering most effective?

Subsurface environments where percolating water gains organic acids. Most active above water table before solutions become saturated.

What is carbonation-solution?

Chemical reaction: CO₂ + H₂O ⇔ H₂CO₃ (carbonic acid), then CaCO₃ + H₂CO₃ → Ca(HCO₃)₂ (soluble calcium bicarbonate). Affects limestone and chalk.

What landforms does carbonation create?

Limestone pavements (Yorkshire Dales), caves (Carlsbad Caverns), dolines, underground drainage systems

What is hydrolysis?

Chemical breakdown of feldspar-rich rocks through reaction with acidic water: 2KAlSi₃O₈ + 2H₂O → Al₂Si₂O₅(OH)₄ + K₂O + 4SiO₂ (orthoclase feldspar → kaolinite + potassium hydroxyl + silicic acid)

What is the economic importance of hydrolysis?

Kaolinite (china clay) production for ceramics industry (Cornwall china clay industry)

What examples show hydrolysis weathering?

Dartmoor granite weathering creating tors, tropical granite weathering profiles (Hong Kong), Brazilian granite saprolite formation

What is hydration weathering?

Certain minerals absorb water molecules, causing expansion and structural changes. Anhydrite → Gypsum: 0.5% expansion. Clay mineral hydration: up to 1600% volume increase.

What is Van't Hoff's Law?

Chemical weathering rate increases 2-3 times for every 10°C temperature increase (up to 60°C maximum)

What does the Peltier Diagram show?

Relationship between mean annual temperature, precipitation, and dominant weathering processes across different climatic zones

Describe weathering in glacial/periglacial climates

Dominant: freeze-thaw weathering. Below 0°C with frequent fluctuations. Rates: Narvik 0.001 mm/year, Spitzbergen 0.02-0.2 mm/year, Alaska 0.04 mm/year

Describe weathering in temperate climates

Both mechanical and chemical weathering occur equally. Moderate organic content, biological activity. Rates: Askrigg 0.5-1.6 mm/year, Austria 0.015-0.04 mm/year

Describe weathering in arid/semi-arid climates

Evaporation exceeds precipitation. Dominant: mechanical weathering, salt weathering, granular disintegration. Rates: Egypt 0.0001-2.0 mm/year, Australia 0.6-1.0 mm/year

Describe weathering in humid tropical climates

High rainfall, high temperatures. Deep weathering extending tens of meters. Iron and aluminum oxides predominate. Rate: Florida 0.005 mm/year (but intensive chemical breakdown)

What is Goldich's Weathering Sequence?

Ranks mineral stability from least to most resistant: Least stable (high-temperature formation): olivine, pyroxene, calcium plagioclase. Most stable (low-temperature): orthoclase feldspar, muscovite, quartz

How do rock resistance values compare?

Marble: 100 kg/cm², Granite: 70 kg/cm², Limestone: 35 kg/cm², Sandstone: 7-14 kg/cm². Note: Freeze-thaw can exert 2100 kg/cm² - exceeds all rock resistance!

How does rock structure affect weathering?

Joint patterns control water movement (most critical factor), folding/faulting create weakness zones, bedding planes provide preferential weathering surfaces

How does grain size affect weathering?

Coarse-grained rocks (granite): high void space and permeability accelerate weathering. Fine-grained rocks: greater surface area but lower permeability.

What are porosity and permeability relationships?

Rate of disintegration closely related to porosity and permeability - explains why sandstone weathers faster than granite despite lower porosity.

How does vegetation affect weathering?

Chemical effects: organic acid secretion, CO₂ production (up to 10x atmospheric levels), humus acidity. Physical effects: root wedging, moisture retention. Can both accelerate (chemical) and reduce (physical protection) weathering.

How does relief affect weathering?

Gentle slopes (

How does aspect affect weathering?

North-facing slopes: cooler, more moisture, enhanced freeze-thaw. South-facing slopes: warmer, greater evaporation, thermal weathering. Critical around 0°C for freeze-thaw effectiveness.

How does altitude affect weathering?

Higher elevations: lower temperatures favor physical weathering, increased freeze-thaw. Lower elevations: warmer conditions enhance chemical weathering. Temperature lapse rate: 6.5°C per 1000m

Describe temperate weathering profile

Surface: mixed mechanical/chemical weathering. A horizon: organic matter, moderate leaching. B horizon: clay accumulation, iron oxides. C horizon: partially weathered parent material. Depth: 1-5 meters typical.

Describe tropical weathering profile

Deep weathering: tens of meters depth (up to 100m). Intensive chemical breakdown: complete mineral alteration to clays. Laterite formation: iron/aluminum oxide concentration. Characteristic minerals: kaolinite, gibbsite, hematite.

Describe arid weathering profile

Shallow weathering: limited by water (<1m typically). Salt accumulation: high evaporation concentrates minerals. Mechanical dominance: thermal expansion, salt crystallisation. Caliche formation: calcium carbonate precipitation. Desert pavement: lag deposits.

What is a slope?

Any inclined surface or hillslope, including level surfaces of 0°. Can be sub-aerial, sub-marine, aggradational, degradational, or transportational.

How does climate affect slope form?

Humid areas: rounded slopes due to chemical weathering, soil creep, fluvial transport. Arid regions: jagged/straight slopes due to mechanical weathering and sheetwash.

What are mass movements?

Any large-scale movement of Earth's surface not accompanied by moving agents like rivers, glaciers, or waves. Include slow movements (soil creep) to rapid (avalanches).

How are mass movements classified by speed?

Extremely slow (0.1mm/year) to extremely rapid (360km/hr): extremely slow, very slow, slow, moderate, rapid, very rapid, extremely rapid

How are mass movements classified by type?

Three primary categories: flows, slides, and heave - each with distinct characteristics and mechanisms

What controls slope failure?

Relationship between shear strength (internal resistance) and shear stress (forces pulling mass downslope). Failure occurs when: 1) Shear strength reduces OR 2) Shear stress increases

What is the safety factor?

Relative strength/resistance of slope compared with forces trying to move it. Involves gravity (slide vs stick components), pore pressure (water forcing particles apart)

What factors increase shear stress?

Removal of lateral support (undercutting), removal of underlying support, loading of slope (water, vegetation, debris), lateral pressure (water in cracks, freezing, swelling), transient stresses (earthquakes, wind)

What factors reduce shear strength?

Weathering effects (disintegration, hydration, dissolution), changes in pore-water pressure (saturation, softening), structural changes (fissures, remoulding), organic effects (burrowing, root decay)

What forces oppose downslope movement?

Friction (varies with weight and angle), cohesive forces (bind particles - clay has high cohesion but reduces with water), pivoting (debris embedded in slope), vegetation (root binding)

What is heave (soil creep)?

Slow, small-scale process occurring mostly in winter. Particles pushed to surface through wetting (75% of movement), heating, or freezing. Move perpendicular to surface, fall under gravity = net downslope movement.

What are soil creep rates by climate?

Temperate: 1-3mm/year. Tropical rainforest: up to 10mm/year. Periglacial: up to 300mm/year. In humid temperate areas, can be 10x more important than slope wash.