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201 Cards in this Set
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L10: Fluvial Processes 2:
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What is stream power?
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-Rate of doing work (potential energy /unit lenth channel)
-determines sediment transport |
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What is stream power equation?
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Ω=ρw x g x Q x s
where: Ω = stream power ρw = density of water g = acceleration due to gravity Q = discharge s = channel gradient |
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What is specific stream power?
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Power per unit area of channel bed
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Specific stream power equation?
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ω=Ω/w= pw(w x d x v)s/w=pw x d x s x v= T x v
where: ω = specific stream power Ω = stream power w = channel width ρw = density of water s = channel gradient d = channel depth v = mean velocity τ = channel bed shear stress |
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What are 3 forms of channel erosion?
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a) Corrosion (chemical)
b) Corrasion- Hydralic/abrasive action c) Cavitation-Pressure differentials (jet-flow one side to other, bubble burst cracks) |
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What are 4 forms of bank erosion (inject sediment-system)?
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a) Hydraulic effects
b) landslides c) Slumping d) Frost action |
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What is entrainment and what are two forces the act against eachother to determine if it occurs?
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-Initial movement sediment when once still (mainly alluvial rivers)
ERODE FORCES: a) Gravity down slope b) Fluid drag (shear stress) Resist forces: a) Friction (particles) b) Cohesion (electromechanical) |
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What are 3 approaches to understanding entrainment praticles?
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a) Critical shear stress
b) Critical velocity c) Lift forces |
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What is critical shear stress and what influence does it have on entrainment?
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define: Threshold value: shear stress value get particle moving.
2 forces: Applied and resist For spherical grains on flat bed: Tcr=n x g x (ps-pw) π/6 x D x tanΦ Tcr = critical shear stress n = packing g = gravitational acceleration ps= sediment density pw = water density D = particle diameter Φ = angle of friction Hydraulically rough beds: Shields eqn Tcr=0.06g (ps-pw)D Threshold of motion Tcr=T0 Stricklers eqn: n=0.015D 1/6 50 Note: Done mm not m |
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What is critical velocity and its influence on entrainment?
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Velocity at which particle will be entrained: relationship b/w grain mevement and flow velocity.
-Use hjulstrom diagram help explain it: Before lowest velocity to entrain= sediment is cohesive After: Sediment is too big to move. |
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What are some assumptions of Hjulstrom diagram?
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-Well sorted sediments
-Smooth channels -Steady flow -Uniform packing Usually in natural wont find these things. |
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What is fall velocity in Hjulstrom diagram?
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Particles no longer in motion (were once moving)- velocity stop and deposit.
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What are lift forces and how do they relate to entrainment?
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2 Sources:
-Velocity differs top/bottom grains -Turbulent eddies |
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What are problems with approaches to entrainment?
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a) All based mean conditions: flow variability, intensity turbulence
b) particle shielding: bed relief, particle fabric. |
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What are 3 modes of sediment transport and briefly describe?
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a) Dissolved/solute load :
-Sources:weathering, human substance, atmosphere- dissolved in water. Measure: Total dissolve solids, patial (measure ions), conductivity tests. b) Suspended load/wash load: -Particles not dissolved travel water current. Wash: Subset-particles <0.064mm diameter-differ size. -Max discharge initial stages of flood. Measure: Per litre suspended sediment -Rate curve. c) Bed load: -Traction (roll/slide) or saltation (bounce) -Cricital shear stress occurs -Velocity H20 determies if occurs Measure: Trap, ratio. |
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What is Bagnolds equation, and what is it related to?
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Qsb= (w-w0) 0.15 x d^0.66 x D^0.55
where: Qsb = sediment transport rate per unit channel width ω = stream power per unit width ω0 = threshold stream power d = flow depth D = particle diameter |
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L11: Fluvial Processes 2
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What are 3 main modes of sediment transport?
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Rate do work determined by stream power
a) Solute load: Supply -limited=chemigraph-dissolved particles b) Suspended: Supply limited: Sedigraph-increased turbulence in current-not dissolved c) Bed load: Transport-limited-less as decreased ability stream move these large sized particles. Bouncing, sliding. |
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What are the two main fluid flows?
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a) Newtonian:
-Linear relation between shear stress and deformation -Not as viscous, viscous stess relates to strain rate (deforming of H20 occurs earlier) b) non Newtonian (Bingham Plastic Liquid): -Viscosity high- resists shear deformation fluid. -Yiel stress: stress before deformation. |
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What are 3 other forms of flow in channel and give threshold values-defining them?
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a) Water flows: Up to 4% volume/ 10% weight
b) Hyperconc : Between 4-60% volume/ 10-80% weight c) Debris flow: >60% volume, 80% weight. |
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Give some examples of videos watched where different types of flow were observed?
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1) Mt Rainier: Rock avalancheparticles air and in flow of rock debris-ice melts under pressure
2) Debris flow: lahar Chile: Viscous liquid allows movement of larger particles on surface fluid. 3) St Julien: Debris flow from Alps in contained channel: comes in surges. increased density-able carr big organic matter as alot sediment in fluids. |
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L12: Fluvial Landforms
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What are sediment facies?
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Sediment unit distinguished by its lithologcial , structural, organic features.
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What is a facies model and what are 3 uses?
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-Summarises specific enviros (how think work)- know processes and hence know deposits.
3 ways: a) Observation framework b) predictive tool c) hydrodynamic interpretations. |
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What are the 3 main lithofacie types in fluvial systems?
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a) gravel-dominated deposits
b) Sand dominated c) Silt dominated Related to bed load types |
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What are the 5 channel types within Shumm's classification of alluvial channels?
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Type 1:
-Relative straight, uniform width -Banks cohesive Type 2: -Mixed load straight -Alternate bars Type 3: meandering pattern: a) Suspended load, near unifrom channel width b) Mixed load sinuous, banks wider at bends Type 4: -Intermediate meander and braid -high w/d ratio Type 5: -Bed load braided streams -High bank erodability -Unstable bar/thalweg |
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What parameters is Rust's classification of alluvial channels based on?
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1) Sinuousity:
S= al (length stream segment)/ sl (length stream axis): straight sinuousity value=1. Channel multiplicity: Braid index: Bl= 2 (sum of bl-length bars)/ rl (reach length) Anastomising: multiple channels-cohesive island material. |
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What are 4 different types within Rust's channel classification?
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Low sinuousity (<1.5), single channel: straight
Low sinuous, multiple channel (BP>1)=braided High sinuous (>1.5), straight (BP<1)=meandering High sinuous, multiple=Anastomising |
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What are alluvial fans?
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Landforms: cone like radiates down slope from point of source
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What is stream power equation for whether sediemnt is deposited on fans?
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Ω = pw (H20 density) x g (gravitational acceleration) x Q( discharge) x s (channel gradient)
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What are some examples of depositional processes?
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a) Processes involve H20:
-Sheets -Channel fills -Sieve deposits (leave debris behind) b) debris flow: water and landslide like after dry period=rain c) Fan types: Dominated by fluvial processes and debris flows:mixed behaviour. |
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What are the characteristics of lowland rivers?
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-Braided streams: > or = to 2 channels divided bars/islands.
Characterisitcs: High gradient, widt/depth ratio, Large variations dischargeBed load transport dominates. |
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What are vertical profile models used for?
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-How sediemnt builds up looks over time
-Local depositonal enviro -Longer term depositional history. 6 vertical profile models: Depend system energy: Trollheim type (steepest) and Bijou Creek Type lowest. |
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What are characteristics of braided rivers-steep alluvial fans?
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-Series stacked debris
-Poorly sorte, massive gravel -Silt and sand poor |
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What are characteristics of vertical proglacial outwash stream profile?
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-Massivepoor sorted gravel
-Minor cross strata gravel -< 10 % sand/mud |
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What is morphology of meandering streams?
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-Sinuous, single channel
-Sinuosity >1.5 -Low w/d ratio -2 types: Fine and coarse grain -Mixed /suspension load channels |
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What is helical flow?
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Cells: drive water down and return to H20 flow.
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What are the sedimentology characteristics of meandering streams?
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a) lag deposits: -In channel depsoits
-Mobile floods Pt bars: Basal and supra platform deposits c) landforms: scroll bars and swales. d) overbank deposits: Levee: Natural linear sediment accumulations-flood related. |
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L13: Coastal and Submarine Processes:
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Why do waves occur?
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Occur interfaces different densities
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What are tides, and their causes?
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-Periodic rise/fall seal level-each point x2 tidal cycle/day
Causes: Moon attractive forces/sun/centrifugal rotation force Sun-moon align: Sprin tides (20% >av) neap tides 90 degrees (20% < av) |
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What are 3 kinds tides?
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high lat: diurnal tides (1 x day)
-Equator: 2 x /day: (semi diurnal) -Intermediate: 2x (asymmetrical) |
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What are 3 tidal ranges?
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Microtidal: <2m
Mesotidal: 2-4m Macrotidal:>4m Range increase with width continental shelf |
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What are impacts of tides on coasts?
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Increase vertical range
-Tidal currents |
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Define waves?
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-Principal source coastal energy
-Interact topography-currents |
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How do waves form?
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Wind on H20 surface
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What is difference between sea and swell waves?
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a) Sea: Move direction storm winds-steep, confused pattern.
b) Swell: Regular waves: long wavelength, rounded crest/uniform heights. |
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What is difference between swell generation in low and high lat?
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Low swells: 35 degrees North/sth equator: <3.5m
High lat: 7m |
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What are 4 factors control height/shape wind waves?
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a)Wind speed-proportional
b) Wind duration c) Fetch (wind travel distance) d) Original sea state |
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What are 3 main wave characteristics?
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a) height: Vertical distance crest to trough
b) periof: Time successive crests pass c) wave length: distance between wave crests |
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What is wave frequency and wave speed eqns?
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Frequency: f=1/T
Wave speed (celerity): C=SQRT g (gravity acceleration) x d (depth H20) |
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What is wave energy equation?
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E (Wave enrgy in Jouls/m^2) = 0.124 x p (h20 density) x g (gravity) x H (wave height)^2
Larger waves-higher energy |
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How do waves break?
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-Waves enter shallow water (<0.5 wave height)-transforms:
a) Power same b)Energy/wave height increase c) Steepness increase, same period d) Crests narrower/oversteeepning e) Instability/breaking On steeper beaches wave break occurs further inshore |
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What are the 4 different wave classifications?
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a) spilling: low slopes, steep waves
b) Plunging: Steeper beaches c) collapsing: collapse as break d) Surging: Steep gravel beaches/ low steep. |
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What is reflection?
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Intersection 2 waves (land and seaward): ie: at cliff
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What is diffraction:?
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Bend waves around obstacle
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What is refraction?
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Bend wave rays.
-Wave celerity (speed) decrease with depth -Bend to zone slowest transport -Converge/spread energy -Waves rarely parallel to beach. |
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What are storm surges and how caused?
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-Short term increases sea level: decrease atmosphere pressure)
Consequences: Floods, inland wave penetration |
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What are seiches?
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-h20 oscillations in closed/semi enclosed basin: change wind direct and pressure-Impulse waves (seismic/major mass movements)
-Seismic: <6.5 and shallow: Pacific Rim |
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What are tsunamis?
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Impulse waves: seismic or major mass moveemtn:
<6.5 seismic, shallow: Pacific Rim |
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What are 3 types ocean currents?
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-Ocean currents: Driven density differences H20
Tidal currents: Ebb/flow tides Rip Current: Develop breakers highst-circulation/wash breaker zones. |
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L14: Glacier Dynamics #1:
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Where are glaciers mainly located now and where were they in Pleistocene (lst glacial period-18000 yrs ago)
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Now: Antarctica/Greenland, other 4% igh latitudes and altitudes:
Comparison: Arctic ocean free of ice today Pleistocene: big sheet took up NW U.S. and Russia and Greenland. North America: 2 large areas- 2 separate centres: Greenland and Hudson bay Canada (>3km thick) |
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What are some areas where major difference in ice coverage was observed from present and Pleistocene comparisons, and where was major change noticed?
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-Antarctica-low difference
Areas with lots change: Greenland and Rocky mountains Major change ice mass northern hemisphere- glaciation relies land masses (high latitiude areas) : lack room sthern hemisphere. |
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What are two impacts of glacials on ocean/land?
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a) Glacioeustasy: H20 volumes - 97% oceans now, 3 % other.
Pleistocene: H20 taken from oceans for glacier storage: sea levels depressed 100-135m, at max: 100-160m. b) Glacioisostasy: -Hydrostatic balance: load/unload -Ice on land causes depression, but once unlodade: rebound=post glacial uplift (residual glacio isostaic recovery-long time after) Max rebound centre as ie was thickest there |
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What controls the glacial erosion?
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a) properties of ice (hardness /debris in it)
b) Ice velocity/ temp (faster over landscape-increase erosion) c) Time (longer causes more erosion) d) Local geology (rock mass strength)-rock resistance |
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What are the two types of glacier classifications?
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a) Morphological classification:
-Constrained by topography (valley) -Unconstrained by topography (ice domes/sheets/caps-terrestrial ice) b) Thermal classification: Temp controls ice behaviour At bed, controls: -Rate deformation (warmer increases) - Velocity/type motion -Glacial erosion/rate-processes |
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What are different parts of glacier mass balance?
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-Accumulation
-Ablation -Movement down glacier -Equilibrium line |
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Further describe the 2 parts and areas within the thermal classification?
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Ice itself:
a) Warm ice: -Warm enough=heat (geothermal)-raise temp to pressure melt point- changes accord to thickness -1 degree celsius/140 bars pressure b) Cold ice: -Below pressure melt point (lack melt H20) -Accumulate fern low temps (high latitude/altitude) -Surface cool winter WHOLE GLACIER: a) Temperate glaciers: -Englacial within glaciers temp at pressure melt point -High erosion/evacuation (lots transport) rates b) Sub-polar glaciers (mix a and b): -Surface temp 0 degrees summer -Parts bed below /above pmp -high erosion c) Polar glaciers: -Strong negative englacial tmeps -No englacial matl H20 -Dry based (no subglacial erosion) |
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What is the mass balance of a glacier?
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Balance between accumulation and ablation.
Accumulation: -Anow -Rain -Regelation (refreeze) ice -Superimposed ice Ablation (output): -Surface melt -Evaporation -Deflation (blow away) -Avalanching -Calving -Baal and englacial melt -Sublime If annual balance is negative after summer and winter balances totaled: decrease mass- thin or retreat If mass positive: increase mass: thicken or advance. (ie: input greater than output) Changes positon of equilibrium line : further back if advance, but firn line moves down. |
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How do we calculte the equilibrium mass balance?
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As (accumulation zone) x Sn (Snow-melted equivalent)= AEL( Area equilibrium line section) x V (mean annual velocity)= Ai (Ablation zone area) x IN *Ice liquid
ie: Input= flow transfer (area equilibrium line) x velocity through section= output glacier |
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Where is the equilibrium line on temperate and ploar glaciers?
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Temperate: Edge previous winter snowline after end summer: firn line
Polar glaciers: Boundary between glacial ice of ablation zone and superimposed ice. |
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L15: Glacier Dynamics #2:
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Define stress (examples) and strain?
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Stress: Force per unit area
a) Compressional (squeeze together) b) Tnesional (Pull apart) c) Tangential (past one another) Strain: Deform- from stress: -Change shape +/or volume -Elongated/shorten (stress direction dictated) -Deform-change volume=dilation |
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What is the strain rate?
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Speed material deforms from applied stess: speed of response.
Low strain rates: Ice-slow deform/response high cumulative strains: Ice particle glacier-travel through will have flattened after long period constant stress. |
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What are common deformations in glaciers?>
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a) Pure shear: stretch
b) Simple shear-layers slipe |
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Why is ice a visco-plastic solid?
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-Particles respond accord to stress
-Creep behaviour Fractures: Creep too slow allow change shape: braks- crevasses-brittle in thin areas, |
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What are crevasses caused by and why wont they be created in some scenarios?
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-Tensile stress, shallow (creep increase with depth)
-Temperate glaciers (close pressure melt point) : rare have >30m =crevasse as ice creeps faster than keep open. |
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What is single crystal analysis of ice found?
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-Elastic recovery -stress=small, irrversible deform if exceeds critical value (plastic deformation)
-Deformation occurs: critical point: elastic limit (cant recover) -Ice has low elastic limit-cruystal strucutre: between viscous and plastic. |
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What is polycrystalline strucutre of ice?
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-Random crystal orientation: less deformable (snowfall)
-Deformation rate along deform planes easier but lack these polycrystalline, meaning decreased ability for gliding crystals. However improved with constant stress-puts back in line. |
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How do crystals deform>?
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1) Dislocations within crystals
2) Move crystals relative to eachother: -crystal growth or decrease with strain -Migrate crystal boundaries -Recrystalisation: matirx-new. |
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What is Glens Law and what does it relate to?
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Relates solely to creep behaviour-glaciers.
e (Strain rate)= A (constant ice hardness) x T (Shear stress) ^n (empirical exponent: av=3) Increase shaear stress:doubled, exponential increasr strain rate. -Ice hardness depends on: -Tmep: increase temp =increase deform -Crystal size: increase=harder -Imurities: increase solutes=softer/ base land. |
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What is temperature and stress dependence of creep relationships ( thresholds)?
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-Warmer ice deforms faster:
-60 degrees to -10 degrees: 2ndary creep -o degrees to -10 degrees: grain boundary melt/regelation Deforms: depend shear stress-increased ice thick/constriction of flow increases this. |
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What is the positive feedbcak associated with Glens Flow law?
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-Exponenetial increase ice mobility: Thermal: Deform ice=generate friction/melt: increase deform ability as increase liquid.
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What is basal sliding?
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It is added to creep-allows for further movement of glacier: needs unfrozen bed-layers water to slide.
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What does basal sliding depend on?
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a) H20 film
Hwo interconnected cavities |
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What are controls on sliding?
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a) Adhesion (below 0 degrees or pmp grips ice
b)Bed form roughness: Bed isnt smooth: need mechanism help get over- regelation sliding: resistance up above object, increased pressure and melts-water layer formed=slides over. Refreezes on downstream side. c) Enhanced creep: High stress upstream: increase strain rates (warm/cold ice): downstream=cod. |
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What are 3 models that describe sliding?>
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Boulomb model: Frictional proportional to normal pressue: unrealistic as assumes rigidity
b) hallet model: -Ice deforms around particles -Constant force not equal to norma load. Detemrined by:' -Buoyancy: ratio particle and ice density) -Velocity toward bed: melt at bed-increase friction. c) Sandpaper model: Close contact between particles: cant deform around them: ice matrix cements. -Appropriate to debris conc>50%. |
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What is stick-slip motion in sliding?
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-Accelerates and stops (ice flow)
-Intense surface melt increases sliding ability. |
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Concerning subglacial sediment deformation, what is the effective bed?
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-Forward motion is 0 as bed is moving forward at same rate as ice above.
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What occurs when basal sliding occurs on subglacial sediment deposits ?
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-Shear stress (ice) > shear strength of sediment=material fails (Coulomb eqn)-forward ice penetrates layer: shear strength > shear stress (ice penetrates substrate)
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What is pervasive deformation?
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Ice through soft sediment-need liquid H20 to occur.
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What do glacier processes mean for geology?
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a) Old models ice sliding applied to Pleistocene era: re-evaluation
b) Forward movement-sediment grinds-erosion efficient mechanism c) Good transprot d) Till units (depositis): discontinuous e) Predict large scale erosion and deposits. |
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L16: Glacial landforms:
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What are 3 glacial erosion processes?
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a) Abrasion
b) Crush /fracture c) Meltwater erosion. |
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What does abrasional erosion depend upon?
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Depends on:
-Relative hardness of ice/rock below (moh's hardness scale: ice=1.5, quartz=7) -Material within ice -abrades bed -Hardness material in ice Other factors: -Ability move ice off bed: pore pressure )decreases abrasion as reduces contact) -Ice thickness -Angular shape: sharper -Removal debris. |
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What does efficiency of abrasion depend upon?
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-Bed properties (resistance) and concentration/hardness material within ice.
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What are 2 types of channel?
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-R- channel (roof open- unstable)
-N-channel (extends to glacial substrate-stable) |
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What does quarrying/plucking (cracking-ice expands in it and causes it to be plucked out and into ice flow) depends on/requirements?
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Depends upon:
-Underlying rock properties: Joints exploited, pressure release, ice wedge (freeze/refreeze) Requires: Shear force of ice loosened particles > shear strength. |
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How does rock pluck in glacier systems>
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- Decrease support: shatters
-Pressure release: freezng -Drainage decrease ormal stress/friction and accelerated basal sliding- shear stress. |
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What is meltwater erosion?
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-H20 channels, conduits, sheet flows: transport H20 causes erosion.
-Rothlisberger (r) and Nye (n) Channels |
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What is the link between erosion and thermal regime?
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a) Cold glaciers:
-Frozen at bed: low subglacial erosion-low debris/abrasion. Larger quarrying. b) Wet-based: -H20 (melt)-liquid: increase debris/abrasion/frost wedging. |
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How is the sediment entrained in glacier?
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Processes:
a) regelation (melt H20 at bed-refreeze-particles attach) b) Large scale refreeze-thin films c) thrusting (faulting- elevate from bed) |
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What are the 3 transport pathways within a glacier?
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a) Subglacial: near bottom: basal zone- dirty.
b) Englacial: Within ice (low concentration) c) Supraglacial: Top of ice |
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What are controls on glacial erosion?
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-Ice cover
-thermal regime -Debris concentration -Characteristics of substrate (resist) -Exposure time to glacial erosion -Pre-exist topography |
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What are glacial forms associated with unconfined flow?
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a) ice sheets/caps: erosion wet based
Positive relief forms: whalebacks etc. Negative relief forms: Grooves etc. |
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Forms associated with confined flow-valleys?
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Negative relief forms: Glacial troughs (systems these)
Cirques, aretes, horns, nunatuks. |
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What are 3 layers of depositional processes?
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a) sediemnts
b) landforms c) Landscapes. |
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What are 2 classifications of glaical sediemnts?
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Genetic:
-Origin sediments: (till-unsorted deposited from ice) -Several varieties (depend process)-melt out till: melted deposits. Glaciofluvial: Alluvial material=deposited melt h20: sorted. Lake sediments (ice rafter: boulder within, melts and sinks bottom) -aeolian sediment,. Descriptive: Diamect: poor sorted sediment. |
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L17: Aeolian processes and landforms:
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What processes does wind undertake?
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erosion, deposition and transportation
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What is winds viscosity like compared to water and how does this change its transport ability?
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lower than water, lower ability to move and transport particles, Mostly transports dust, some sand (desert), rarely fine gravel.
H20: 1000kgm-3 vs air =1.22 kgm-3 |
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What are some wind transported landfroms?
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-Deserts (landform)
Non-desert: Loess cap Dunedin |
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Why is air easier to get flowing and what is difference between air and water transport particles?
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-Ability water flow alot easier (less energy get going)
- Particles in air settled (as cant move them) whilst still moving and entrained in water at lower velocity. |
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What is turbulence determined by?
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-Atmospheric stability: stable=low, heat ground=turbulnece, flow air over obstacles
-Morphology of surface: landforms/vegtation (structures) -Effective wind: boundary layer related roughness (forest rough to smoother in bare surfaces) |
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What is the boundary layer?
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Roughness element: 0 wind speed: average for forests just below the highest trees canopy
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What is entrainemnt and what are conditions required for it to occur?
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-Particle mvement
-Turbulent lift + shear stress> normal stress + friction. |
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What is the difference between the fluid and impact threshold for particles (range from silt small ones to coarse sand)?
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Fluid threshold: Wind speed required to entrain if particles stationary.
Impact threshold: Less energy to entrain or move as kinetic energy from other moving particles starts off motion (hence lower graph) |
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What are the controls on movement of aeolian moved particles?
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-Cohesion
-Mass (increase energy) |
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What are some landforms created by sand dependeing on particle size?
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Loess< Dunes< Lag deposits
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What are some erosion processes and how can erosion be reduced by formation of particles in landscape?
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Deflation: Loose material blown away
-Entrain: blow finer, leave coarser lags (shields finer deposits). Residual materials= Gibber Plain Aussie.-desert pavement. |
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How does abrasion occur?
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-Saltating particles hit
-Wear from traction -Occurs within: break down to smaller sizes, or abrasion by hitting rock and wear down Dependent on tools: ice/ sand |
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What are controls on abrasion?
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a) Rock/tool hardness (relative)
b) Wind velocity/duration |
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Describe the 3 main types of sand transprotation?
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a) traction :
-Roll/slide (too large saltate) b)Saltation: -Impact threshold applies - Too big for suspension c) Suspension: -Aussie dust loess -Fine, long distance |
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What causes and what is process that leads to depositon of particles via wind?
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-Velocity and or turbulence decrease (fall velocity)
-Supension-saltation-traction -Depositon=Loess Oamaru |
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What is a desert pavement and how does it prevent erosion of particles beneath?
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-Over time, small particles become moved, leaving larger pebbles etc behind: these shield the finer particles beneath-leave desert pavement that lacks any movement by the wind.
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What are Yardangs (aeolian formed structure)?
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-Structurally controlled deflation hollows
-Abrade weak material, leave strong. -Increase deflation. |
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What are sand seas (ergs)?
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-Dune dominated landscapes
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How do we define the difference between dunes and ripples?
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Dunes:
1-30m high, 10-500m wavelengths Ripples: 0.1-5cm high, 0.02-2m wave length. |
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What are some dune shapes?
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a) Barchan
b) parabolic c) Akle (fish scale) |
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What are loess sheets?
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-Cool to cold deserts
-Silt size particles glacial outwash -Sources: Continental shelf and Sthern Alps |
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What is role of coastal dunes?
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-Coastal process role
-Dune to beach interactions -Sediment store -Coastal aggrade or erode. |
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L18: Volcanic processes and landforms:
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.....................................
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Define volcanic processes?
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-Moveemnt molten and or solid rock: undergo slow deform to earth surface.
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What is difference between extrusive and intrusive volcanic activity?
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Extrusive: Magmaeruption: lava/ fragmented material explosion-landfroms formed and changed.
Intrusive: Move rock in earth: uplift. |
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What are volcanoes and what are vents inside them/ where are they all distributed?
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-Extrusive form volcanic activity=ash/lava.
Vents: Gas build up- lava/gas escape. CLUSTERED: 60% of active volcanoes clustered on Pcific Rim. |
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What is difference between acidic and ultrbasic volcanoes (igneous rock)?
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Acidic : > 66% silica
Ultrabasic : <45% silica Determines explosivity |
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What is lava?
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Magma: cools and degases to decrease pressure= lava.
-Viscosity affects behaviour (temp/compositon) |
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What are pyroclasts and tephra?
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Pyroclasts: Shattered rock (explosive volcanism): ash<4mm
Pyroclastic flow: eurpt: lots gas/ash: Taupo. Tephra: Air fall deposits in soil (mixed sizes) |
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What are some water sources with volcanism and what can interaction between two create?
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Magma=4% H20
H20 mixed with volcanoes =meteoric CAUSE: -Hydrothermal activity: erupting superheated geyser. -Mass movements: volcanic debris and H20=lahar (high speed , long distance, thick depostis) |
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What are fissures and cones?
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Fissure: Widespread (mid ocean ridges) filled lava
Cones: Central vents/ pipes (successive lava flows): shield volcanoes-Mauna Loa underwater. |
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What are the different volcano types?
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a) Caldera: Exploded central area: 0.1-1m yrs eruptive activity. (lyttleton)
b) Cinder/ scoria cone: Fragmented material (30 to 40 degrees) =Rangitoto: 1-10 yrs eruptive activity c) Stratovolcanoes/ composite cones: - Most common -Mix lava flows/pyroclasts -Concave slopes Layers sediemtns, pipe conduit in middle may collapse. d) Calderas: Collapsed structures-summit large volcanoes. -Drain magma chambers/ roof collapse |
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What are Maars and domes?
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a) Maars:
Shallow craters < 1km diameter -Formed: explode gas charged magma (ACIDIC) b) Domes: Viscous magma. |
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What are some eruption types? Morphological controls of?
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-Volcano size
-Volcano shape -Material produced -Material distribution eg: energy released by eruption average= 10^12-10^15J , Mt St Helens: 10^17J. |
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What are Summerfields 8 styles of eruption classifications based on?
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a) Energy density
b) Magma type c) Effusive activity d) Explosive activity e) Structures formed. |
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Give some examples of volcanic eruption types and how differ?
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Icelandic: Basic, low viscosity, weak explosuion: broad lava cones (More flow typ, thick effusive,low energy)
Volcanism type: Acidic, viscous, moderate explosion, ash cones/ explosive craters Krakatouan: Acidic, viscous, no effusive -cataclysmic erupti |
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What is pyroclastic flows and what are some exmaples of their deposit structures?
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-North Island: Block flows, ash flows
-High velcoity gas flows- tephra, gas carried several kms to atmosphere -Laminar/turbulent flow DEPOSITS: a) Surge deposit (dust) b) Pyroclastic c) Air fall ash |
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What are igneous intrustions?
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-Penetrations mobile molten rock to host rock: sills formed etc
Impacts surface landforms: erosion, diff rock mass strength, draiange. |
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L19: tectonic geomorphology:
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....................................
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What are 2 main views of what geomorphology is?
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a) Analysis landforms : exogenic> endogenic (tectonic etc): landforms still provide endogenic indications,
b) Morhology earth surface +slope/scale accord problem. |
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What is tectonic geomorphology?
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-Mix tectoni process and topography vs surface process tear down. (short-exogenic instrumental record) vs longer term (endogenic)
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What are tectonic processes/types?
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-Earths crust motion: lateral/vertical move
a) Extension b) compression c) Uplift (mass waste) d) Subside (downwards ) Uplift force vs erosion potential |
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What is difference betwee rock uplift and surface uplift?
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Rock Uplift (UR): change vertical position respect to datum (SL-sea level)
2 parts to it: UR= UT( Tectonic uplift) + UI (Isostatic) Surface uplift (US): change elevation land respect to datum (SL): US = UR-E (Exhumation) |
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What is exhumation
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Strip overlying rock material
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What is difference if nor erosion vs erosion occurs?
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Erosion: Rock uplift > surface uplift
No erode: Rock uplift=surface uplift. |
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What is response of rock uplift after erosion?
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Isostatic compensation: Raise rock -net lowering however.
I |
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What is the isostatic compensation equation?
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UI= pc(crust density) / pm (mantle density)
US= E ((pc/pm)-1)) For every 100m exhumation, 82m surface uplift -assume no tectonic uplift involved. |
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What are the implications of isostatic compensation?
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- Uplift ceases non tectonic uplift (no material to erode)
Sustained: -Crustal thickens under mtns --Root sustains elevated topography after cease uplift -Postorgoenic erosion |
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What is isostasy infuenced by?
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-Size of load
-Strength of crust. |
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What is flexural rigidity?
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- Rebound / subsidence large areas (size of load and strength crust determines).
-Flexural upwarp away from load, flexural downwarp- below load. Types: Orogenic loading Glacial loading Sediment loading (offshore sediemnt uplift land ) |
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What is different between spatial scales of flexural rigidtiy and erosion?
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Flexural rigidity: Large scale: 10's to 100's km
Erosion: Localised: < 1km individual valley |
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What occurs when isostatic compensation and erosion combine for mtn range?
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Uplift occurs:
-Base level rivers dissect land -Isostatic compensation, erode river valleys (Causes deeper vallleys) - Crustal root thins- mean elevation/ peak elevation decreases. |
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What is landscape response to tectonics?
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-Base level change (SL)
-Rivers/streams -Hillslopes -Shaking (increase mtns) |
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What occurs within rivers and streams to make them change landscape?
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- Spatial variation uplift (steep vs flat)
-Knickpoints: propogate upstream. -External controls: Uplift/subsidence, sea level fall/rise. Base fall: incise fluvial system - channels erode (steepen river slopes-basin outlet) Opposite increase base level: streams run ocean (aggrade) |
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What are 2 different slope types and their response to tectonic uplift?
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a) Subthreshold slopes: -Soil mantled, low to moderate gradients, slope increasewith increased uplift.
b) Threshold slope: > 30 to 40 degrees, soil strip (transport limited) -Cant keep steepening - landslides instead uplift: eg: Lake Canary (near Hokitika) |
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What are some tectonic settings/ types tectonic boundaries?
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a) Extensional margins
b) Compressional margins -Transform margins (Strike-slip) |
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What is an extensional margin?
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-Zones crustal divergence
-Causes upwelling magma. Landforms: -Escarpments, -Rift valleys -Volcanoes -Gently slope streams - |
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What is a compressional margin?
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-Collisional plate boundaries: orogenesis.
-Linear belts uplift=cause other processes: eg: Himilayas Characterstics: -High rates crust deform/ uplift/incision -Steep slopes, landslides -Dee gorges -Lots sediemnt -Suture zones Continental lithosphere (Himilayas), Andes: Ocean and continental, oceanic : Bismark Arc. |
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What is the Pacific- Aussie boundary an example of and explain?
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-Transrom margin (strike-slip):
-extension (transtensional) -Compression (transpression)-fault parallel mtns -Mostly transform: both parts convergence -Pure transform rare: transpressional. Features: Offset streams, linear streams, sag ponds. FEATURES: -Pacific under Aussie to North, normal in middle, Pacific over Aussie in South. -Reverse subduction zone |
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How are the Southern Alps a steady state mountain range?
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Uplift=c11mma-1
Erode=c11mma-1 -Uplift generates high topography, west circulations (cant increase as ppt too high). |
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L20: Geomorphology and climate:
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..................
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What is climate?
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Long term weather condition average (temporal and spatial scales)
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What are the 2 scales and subsets within each for climate?
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Temporal:
a) Tectonic: Climate zone change= continent /ocean arrangement, CO2 conc b)Intermediate scale: 1000's yrs, seasonal distribution solar radiation c) Smalll: yrs to decades: aerosols (volcanic eruptions) SPATIAL SCALES: a) Large: Climate zones- hot vs polar (ppt) b) Small: Sunlight adjacent slopes Temperature, ppt, wind, humidity |
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What are 2 different landforms that can tell climate records from>?
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1) Moraines:
-Last glacial max (22000 yBP)= 5 degrees av lower than now -Equilibrium line moves down glacier: thicken/advance -Dating: Be10 isotope Problem: erosion terrestiral record 2) Lacustrine and marine records: -Continuous -Short range (lacustrine: v close landscape vs moraine: larger time, further from land) Problems: How events embedded sediemnts, records=dated eg: Sth Westland Lakes, N.Z. |
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What was fond concenring climate records in the South Westland Lakes of Moeraki and Paringa?
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Paringa: Dating: recently- use Cesium 137-based cesium put atmosphere nuclear testing: 50's to 60's
Moeraki: Larger lake (captures Lake Moeraki) RECORDS: (Graph) -Lighter part core= landslide finer grained Greyqake -Magnetic susceptibility (measure soil magnetic mineral conc)- decrease with more Greywacke -Pulse sediemnt -Red pulse: earthquake turbidite (lots rock) |
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What were some other ways of dating material /events in lake Moeraki area?
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a) Leaf macrofossil (14C)-model age
b) Rain gauge : 1956-2009: record= 439.4mm-correspond to landslide- lots rain before and after- sediemtn input to system 1300 yr return period. c) Aerial photos: 1946-1984: Change river landscape- see where landslide came in and caused braiding, forest destruction, widening river etc. Whereas another one- disconnected from lake wouldnt be shown in lake record. d) Seismic cycle deposition: Mass movement (lots sediemnt stirred), stacks sediement due landslide, back to normal =dark lines and orgnaic material. |
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What are ice cores and how are they used to decipher climatic changes over time?
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-continuous record (snow accumulation)
a)Isotopes of H20 (Deuterium, and 18O -stable palaeo temp proxy) b) Atmosphere gases: CO2-driver atmosphere temp, CH4, SO2-volcanic activity ice below density- air bubbles record after 1000 yrs) |
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What do the ice record indicators show ?
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S18O: Higher values=warmer: long periods glacial, short interglacial
CO2: Correlates with temp: higher-higher CO2) -Sulfate: pin pint erupt. Constraints: 6-800000 yrs In quarternary ( Pleistocene :2mBP to 10000BP) and Holocene (10000yrsBP to now) |
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What were the 2 cycles once in Quarternary period?
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Early part (2m.a. to 800000):
-Short, symmetrical cool periods -40 000 yr periodicity Later (post 800 000): -Cycles longer (100 000 yrs) -Asymmetric: slow cool rapid warm -Sawtooth pattern eg: Last interglacial: (120 0000y.a.) slow cool to last glacial max (22 000 y.a.) then Holocene last 10 000yyrs. |
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Why has there been a change in pattern of interglacial etc periods?
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Hypothesis 1: Decrease CO2, concurrent cool planet
Hypothesis 2: Glacial geomorph threshold: early ice sheets rested weathered material (soil= low basal resistance) , mid latitude ice sheets, then stripped away regolith anf exposed crystalline bedrock (high basal resistance-decreased respinse): thin flat ice sheets. |
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What is and how does orbtial forcing fit in with change quaternary cycles?
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-Shape earths orbit around sun: seasonal distribution solar radiation.
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What are the Milankovitch cycles?
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a) eccentricity (change earth orbit- 100 000 periodicity-correspond glacial/intergalcial
b) Olbiquity (41 000 period) - titl earths rotation axis c) processeion equinoxes (22k periodicity) -wobble earths rotation axis. |
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Why is it hard state overall reason for change cycles?
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-Earth system is complicated than set variables (feedback loops etc)
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Why are plaeotemperature events abrupt and globally synchronous?
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-Rapid reorganisation ocean currents leads to change pattersn heat distribution ( High solar radiation equator-redistribute to polar regions) : drive atmospheric and ocean circulation.
Thermohaline circulation system-salt and temp H20: Cooled, salty, deep current travels south upt to East side world, picks up warmer water eqautor , drives back to west side . eg: Younger Dryas event : Decreased transprot of tropical H20 -Nth Atlantic-rapid cooling. |
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L21: Landscape evolution:
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............................
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How do we find long term landscape evolution?
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-Try apply recent exogenic (small scale/time-space) to long term (assume stationarity)
-Reconstruct processes/history of past using techno etc models! |
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What are 5 controlling factors in landscape evolution?
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a) Tectonics (earth deform)
b) Climate (ppt/temp) c) Topography (increase=increase potentioal and therefore kinetic energy) d) Geology e) biology |
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Explain tectonics influence on landscape evolution?
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-Surface uplift (rate change landscape elevation: perturbation cascase energy )
reaction time: time start response perturbation Relaxation time: System adjust to change (time) eg: Stream: a) low stream power/ increase sediemtn =aggrade b) high stream power/ decrease sediemnt =degrade Perturbation, period no reaction, stream bed lifts, incision after another pertrbation. |
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Explain climatic effect on landscape evolution?
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-Determines surface processes: ppt
-Indirect: vege -Impacts style/pace landscape evolution |
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What is topography influence on landscape evolution?
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Releif: (highest/lowest points)
-Affects change pace -Orientation- wind (Sthern Alps-ppt) Steep slopes=mass move Subdued=fluvial, decrease rate change. |
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What is geology's influence on landscape evolution?
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-Structure rock- strength
Fracturing: degree tectonic deform- increase relief- less effect of geology as releif determines erosion etc more. |
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What is biology's role in landscape evolution?
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-Vege cover: acts through :
-Hydrology -Erosion potential (protect) -root protection -Change landscpe devt depeng chang e cover land: C.C. or anthropogenic. NZ. : remvoe pines=increase erosion when trunks fall out. |
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Models: Simlified: Conceptual?
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-Descriptive/qualitative
-Organise time devt 2 frameworks: a) transient response to landscapes= Models: describe change conditions-climate etc=changes trigger time dependent response. b) Dynamic equilibrium-condition variability over time -av condition. Steady state landforms (Sthern Alps) |
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What is the key ideas behind W.M. Davis and Geog cycle of erosion: Transient model/ what are problems with it?
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Model:
a) low relief, rol hills UPLIFT b) Incised valleys, low relief uplands c) High releif, steep slopes EROSIONAL DECAY d) Medium releif, moderate slopes Ends peneplian: erosion surface without releif. PROBLEM: No climatic role |
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What is John Hack and dynamic equlibrum?
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-Erosion, transport, deposit alter land (overall landscape characters=same)
-Tectonic uplift increase, flattening, drops, slow isostatic compensation. -Dynamic equilibirum: gross form relief mtn system sustained. Tectonic uplift: Rates rock uplift> erosion rates: surface increase/relief devt. |
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What are physical models, and what are problems with them?
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-Scale (hardware) model
-Process manipulated: result observed/measure: Problems=scaling, simplify reality eg: Stream table exercise |
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What are mathematical models? Give some approaches?
|
Scale: a) Small=slope process
b) Linked processes in landscape Problem: Hard integrate complexities 2 appraoches: a) process models b) transprot laws |
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What are process models (math models)?
|
Force balances represent thresholds:
a) simple: Factor safety eqn (mass move) b) elaborate: Simulate rain and where it goes using GIS. |
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What are transprot laws within math models?
|
-Eqns define relationship governing variables and sediment move. Laws=characterise system behaviour.
-Solved characteristic froms (slopes) , processes. qs (rate sediemnt transport)= D (rate constant) x S^n (slope-1 linear diffusion, <1 non-inear). |
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What are 4 main landscape types?
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a) Steady state: Tectonic uplift=erosion ( mass balnce): sthern Alps
-Solved characteristic forms (slpes) for sporcesses (soil creep) b) Collisional orogens: Mass mtn range increase until erosion limits grow c) transient: Knickpoints: propogates different rates/streams (accord stream power) d) Relict: Produced former climate (glaciated)-disequilibrium. |
