3. Earth Processes info

Define litosphere and asthenosphere

Lithosphere = part of crust broken into giant tectonic plates

Asthenosphere = weak hot flowing zone at top of mantle

Oceanic vs Continental age

Continental = up to 4.5billions

Oceanic = < 200 million years old

Oceanic vs Continental material and density

Continental = granitic 2.6g/cm3

Oceanic = basaltic 3g/cm3

Oceanic vs Continental thickness

Continental = 70km

Oceanic = 5-10km

All evidence for plate movement

• Apparent jigsaw fit of continents - SA and Africa

• Fossil correlation - Mesosaurus SA and Africa

• Rock and mountain correlation - Zircon dating so same rocks made in same time - Canada/Greenland and North Europe/Scandinavia

• Palaeomagnetic correlation - alignment locks as plate cools showing evidence of seafloor spreading

Theories of plate movement from best to worst

• Slab pull, ridge push + small bit convection currents

• Convection currents

• Expanding earth

• Hydroplate

Explain divergent/constructive oceanic boundary - (faulting type, processes, landforms)

• Normal faulting

• Two oceanic plates move apart driving plate movement by ridge push

• Long ocean ridge forms, shield volcanoes(low silica lava forming)

Explain divergent/constructive continental boundary - (faulting type, processes, landforms)

• Normal faulting

• Thinning of the crust in the middle creates graben(dip), terraces coming out from graben, fault scarps = vertical displacements of rock

• Hot springs

• Mostly shield volcanoes as oceanic magma but sometimes silica from continental makes stratovolcanoes

Explain ocean-ocean convergent/destructive boundary - (faulting type, processes, landforms)

• Reverse faulting

• Island arc and ocean trench, back arc basin, stratovolcanoes

• older, colder oceanic plate subducts

• Accretionary wedge forms between plates

Explain continental-continenral convergent/collision - (faulting type, processes, landforms)

• Reverse faulting

• Fold mountains

• Orogeny = mountain making effect

• Accretion

Explain Oceanic-Continental convergent/destructive - (faulting type, processes, landforms)

• Reverse faulting

• Oceanic plate subducts

• Fold mountains, stratovolcanoes, trench

• Drives process of slab pull

Conservative/transform plate boundary - (faulting type, processes, landforms)

• Shear stress

• Earthquakes

Oceanic hotspot - (faulting type, processes, landforms)

• Island chain/shield volcano

• Moving oceanic plate creates chain of islands over stationary rising magma plume

Continental hotspot -(faulting type, processes, landforms)

• Strato/composite volcanoes

Name all tectonic forces, what they are and where they are

• Confining stress - pressure from above

• Compression - rocks pushed together - convergent

• Tension - rocks pulled apart - divergent

• Shear - rocks pushed past one another - shear

Explain how deformation changes with depth and speed of stress

• Surface = all brittle deformation

• Deep in mantle = all elastic deformation

• Mid depth

  • Slow speeds = all elastic deformation

  • Mid speed = plastic deformation

  • Fast speed = brittle deformation

Name all 7 types of mass movement

• Rock falls

• Debris/mud flows

• Rotational slides

• Slides

• Slumping

• Heaves

• Soil creep

Explain heaves/creeps

• Slow, gradual process

• Individual soil particles are moved down slope by wetting, freezing or heating

• Soil creep can form terraces

Explain flows

• Continuous flows that change shape of regolith

• Regolith size is usually smaller - rocks/mud/fine silts

• Mudflows = fast, wet flows of mud

• Debris flows = fast flowing accumulations of water containing soil and rock fragments

Explain slides

• Landslides of any material/regolith

• Rotational slides(slumps) produce a series of steps/terraces

• Occur when an entire mass of material moves along a slip plane

  • junction between two layers of rock

  • A fault line

• Slide material generally tends to maintain shape

• landslides

  • Loose rock/stones/soil moving down slope as shear stress is greater than shear strength

• Slumps

  • Occur on weaker rocks and have a rotational slide along a slip plane

Explain falls

• Occur on steep slopes

• Often caused by weathering

Condition for mass movement to occur

Shear strength > shear stress

Exogenic vs endogenic factors affecting mass movement

Exogenic

• Precipitation, weathering, human activity, land use change

Endogenic

• Lithology, human activity, pore water pressure, weakening of cohesion, undercutting of slope, organic effect, road building(undercutting), excavation, deforestation, loading from houses