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GEO1213: Earth System Science: Our Changing Planet > Geosphere > Flashcards

Geosphere Flashcards

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1
Q

Overall, what are landscapes formed by?

A

Running water, fluvial processes of erosion and deposition in non-freezing circumstances

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2
Q

Give the 3 types of models of landscape evolution

A
  1. Numerical - computers, simulation
  2. Experimental - physically building a mock-landscape
  3. Conceptual - drawings/sketches/diagrams stemming from an initial theory
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3
Q

Give an example of an early conceptual model

A

Davis, W.M (1900) ‘Cycle of Erosion’

  • Landscapes that ‘aged’, young (rapid uplift, incisions and down cutting, steep, jagged) to mature (flat, few hills)
  • Sketched by Summerfield (1991) (take note of the altitude/time axes and the annotations; altitude, max relief, peneplain…)
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4
Q

Define potential energy, base level and peneplanation

A

Potential energy - to do work (erode), determined by land surface height above a ref. level

Base level - level to which landscape erodes (sea?)

Peneplanation - decline in surface elevation/gradient/relief over time as it erodes

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5
Q

What did Davis’ model not account for, and how was it modified (any competitors?)

A

Renewed uplift - landscape rejuvenation
Climate - landscape evolution dependent on its intensity/changes
Geology - rock structure/lithologies influencing drainage patterns

Competitors - Penck (waxing/waning developmentl more gradual mountains) & King (against a final, fully flat landscape)

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6
Q

Explain 2 types of uplift.

A

Orogenic = by horizontal compression and folding of Earth’s crust - produces mountains with the deepest roots due to lightweight yet v. thick crusts (subduction); fast rate of 4-10mm/yr e.g. Andes

Epeirogenic = by vertical elevation of large blocks of crust - produces plateau-like landforms, slower rates of 0.1mm/yr and 0.015mm/yr e.g. Colorado/Decan plateau

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7
Q

What percentage of the height lost due to erosion is regained by isostatic adjustment of crust?

A

80-85% (1/5)

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8
Q

Surdace uplift = ?

A

rock mass uplift - exhumation

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9
Q

What is denudation? Give 3 mechanisms of this. What are they dependent on?

A

The decline in surface relief, elevation and gradient as a result of moving water eroding surface:

  1. Physical e.g. frost-thaw, sand, abrasion
  2. Chemical e.g. dissolution, rock-type
  3. Biological e.g. roots (release of org. acids)

Dependent on TEMPERATURE and MOISTURE

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10
Q

What are the percentages for the different types of load?

A

Dissolved (solution) - 20%
Suspended (sand, clay) - 70%
Bed (sand, gravel) - 10%

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11
Q

Give 4 types of re-depisted landforms

A
  1. Colluvium (foot slope)
  2. Alluvium (floodplains)
  3. Deltas/estuaries (inter-tidal)
  4. Fans (basin floor)
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12
Q

Give 5 controls on denudation

A
  1. Basin relief - both fall
  2. Climate & vegetation - no rainfall, no erosion (lowest dundation at 800mm/yr)
  3. Lithologies, tectonics, storms
  4. River incision rate - rate increases as incision increases
  5. Glaciers - deepen valleys, u-shaped, material removal may promote uplift
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13
Q

What is the main control on mountain height.

A

Glacial erosion - mountain surface area concentrated at snowline (Egholm et al. 2009); climate&latitude control height to which uplift can drive mountains

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14
Q

What is Global Sediment Yield?

A

~25-28x10topowerof9 t/yr = far greater than global mean denudation for surface lowering and isostatic recovery
Largest areas of sediment yield = Bengal Fan and New Guinea Fan (lots o’ carbon)

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15
Q

Outline features of the base level

A

The sea level, frequently changes by

  1. Eustatic controls; sea water/ice volume, thermal expansion (higher oceans 40M yrs ago)
  2. Isostatic adjustments; surface loading/unloading
  3. Tectonic controls; on ocean basin volume
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16
Q

How is mass conservation applied to the landscape? What is the formula for ‘change in land surface elevation’?

A

Mass cannot be created/destroyed; means there is more/less sediment arriving than leaving, sediment always moving

Amount of uplift + balance between sediment supply and removal

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17
Q

Equations and units for ‘Height change due to erosion (m)’ and ‘annual change in bed height due to sediment movement (m/yr)’

A

Volume removed (m3) / surface area (m2)

Qs(in) - Qs(out) / river bed area

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18
Q

When are landscapes in equilibrium? GIve 3 types (different scales).

A
  1. Dynamic - long 10(4), cyclic, slow
  2. Steady-state - 10(2), graded, century scale, NO net change in elevation, periodical rise/fall
  3. Static - 10(1), no change at all, a rare occurrence
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19
Q

What are the 2 main ways to reach equilibrium? Give a feedback loop for equilibrium based on a steady climate.

A
  1. Long-term evolution; uplift = erosion
  2. Shot-term evolution; sediment in = sediment out

Precipitation -> erosion -> relief -> precipitation etc.

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20
Q

What is qw, S and qs in terms of power laws?

A

qw; water flow rate = depth x velocity (m2s-1)
S; downstream slope of river bed
qs; sediment transport rate (m2s-1)

21
Q

What are the 2 main sediment transport processes that use these power laws?

A

Diffusive - sediment movement due to surface gradient

Advective - due to water-driven processes

22
Q

What is the crucial feedback between landform and process? (Gilbert GK, 19th C.)

A

River form/shape -> water distribution -> sediment transport -> affects form etc.

23
Q

How do topographic changes caused negative feedbacks (dampening effect)?

A
  1. Sediment transport rate proportional to slope/water-driven processes
  2. Slowing of erosion results in supply/removal imbalance, so surface lowers
24
Q

Hillslope profiles

A

Good examples of equlibrium being reached:

  • Uplift = erosion
  • qs increases downslope, where diffusive processes dominate
  • Eventually, qw dominates, so S again increases
  • Rates of sediment transport strongly dependent on slope, strong neg. feedbacks, tendency towards stable, equlibrium forms
25
Q

Define drainage basin, river flow/bank full discharge and river capture.

A

Drainage basin = an area of land that all drains to the same outlet; defined by topography, mountain ranges

River flow/bank full discharge = amount of water passes by time unit through section of river, measured in cumecs (m3s-1); bankfull is discharge that fills a stable alluvial channel to elevation of active floodplain

Discharge (Q) = Width (W) x depth (h) x Velocity (V)

River capture = LT evolution of river, headwater erosion, re-routing, leading to DB area change e.g. Indus

26
Q

Drainage basin splitting drivers?

A

Uplift and denudation (using models e.g. Bonnet 2008)

27
Q

Outline the role of erosion/deposition, tansport capacity and sediment delivery ratio in basin hydrology/sediment transport.

A

Erosion/deposition - ability of water to erode/transport depends on competence of flow and size of sediment (Hjulstorm Curve!)

Transport capacity - measure of total amount of sediment that flowing water can carry, sharp curve (critical threshold between trans & vel.)

Sediment delivery ratio - fraction of sediment eroded from slopes that reaches drainage basin outlet = sediment output / eroded from slope (tends to decline downstream, wider valleys, more deposition…)

28
Q

Explain the source-to-sink concept.

A

Sediment moving, like jerky conveyor belt, storage periods

  1. Small-scale sediment stores; temporary, eventually incise e.g. braided islands, glaciations
  2. Large-scale; preserved, e.g. HUGE Amazonian stores, deltas, alluvial fans, shelves (12.5Mkm2 Bengal)
29
Q

What us sediment accomodation space?

A

Space available to store sediment, rarely in mountains
Affected by:
1. Sea level rise; inundation = larger capacity = aggradation
2. Tectonic uplift; steepening = increased GPE = increased fluvial incision/erosion = more sediment downstream

30
Q

What is the river long profile and how is it controlled?

A

Curves (often concave) showing the change in height of river bed moving downstream from headwaters to sea.
Controlled by:
1. Discharge (increase downstream)
2. Sediment load (increases at slower rate bc storage)
3. Sediment size (decreases bc finer particles)

31
Q

Give 3 main types of river morphology and what controls their river patterns?

A
  1. Straight; rarely natural, oscillation, uneven…
  2. Meandering; exaggerated oscillations, depostion/vegetation on one side (think of thalwegs!)
  3. Braided; lots of movement but high sediment supplies and lack of vegetation

Controlled by:
Slope & discharge - braided on steeper slope than meandering with same discharge (steeper slope forms when river needs it!)
Bank strength - limits widening by erosion (lateral sediment supply), roots/veg?

32
Q

Outline the Lane Diagram

A

Shows relationship between sediment size and stream slope, how these result in aggradation or degradation

  • Steep slope = more water = degradation
  • Large sediment size = coarse and heavy = aggradation
33
Q

How is sea level change controlled and describe the coastal zone.

A

Controlled by eustatic (ice, thermal expansion) and isostatic (adjustment, loading/unloading) changes

Distribution of coastal zones affected by sea levels

  • Sub-aerial = 20,000 yrs ago flooded
  • Continental shelves, shallower waters 100-200m depth
  • Coastal plain with waves/beaches further in (recent)
  • Morphodynamics; feedback systems = external environmental condition -> processes -> sediment transport -> morphology -> stratigraphy?
  • Sediment budgets vary based on type of coast (estuarine or deltaic)
34
Q

What is the role of waves, tides and the tidal range?

A

Waves - wind/seismic activity, deep water wave height determined by wind speed, frictional drag (L/2) etc. (recall A level wave knowledge!)

Tides - attraction of sun & moon, neap (weak, 90) and spring tides (strong parallel)

Tidal range - highest to lowest water level, controlled by bathymetry, shelf width, determine extent of intertidal zone

35
Q

How are erosional and depositional coasts different? What controls deposition?

A

Erosional - high energy, low sediment input; controlled by wave environment, lithology, morphology, tidal action, climate etc.

Depositional (controlled by sediment size, water energy and salinity) - low energy, high sediment; gradient depends on sediment size, beaches

36
Q

What are the controls on sediment supply and dispersal at coasts?

A

Supply - catchment characteristics (relief, size, lithology, tectonics), climate, soil, vegetation, humans

Dispersal - river flow, sediment load/amount/size, strength of tidal currents, buoyancy of river water, waves

37
Q

Outline types of deltas and their dominant processes.

A

Fluvial - river dominated, elongation e.g. Mississippi
Wave - wave dom, cuspate, cutting/calving
Tidal - tide dom, estuarine

Estuaries to deltas over time with increasing progradation, decreasing transgression

38
Q

What are the human impacts relating to the coastal zone?

A
  • Changes in sediment delivery to ocean e.g. soil erosion, dams
  • Loss of sediment supply = reduction in aggradation, increased vulnerability to flooding and rising sea levels
  • Long-term subsidence from tectonics
  • Delta subsidence e.g. Mississippi delta sedimentation declined by 1.7mm/yr in c. 100 yrs
    By 2050:
  • Loss of land for 1m relative sea level rise
  • Millions of ppl on deltas affected e.g. Bangladesh,
    Mekong
  • Increased population pressures; subsurface abstaction of oil, water, gas etc.
39
Q

Outline the role of vegetation (x6)

A
  1. Slope stability
  2. Hydrology
  3. Soil quality
  4. Sediment trapping
  5. Atmospheric composition
  6. Surface roughness
40
Q

Give 4 controls of rainfall.

A
  1. Atmospheric circulation; convection cells
  2. Continental isolation; areas further from ocean, less rainfall
  3. Rain shadow effects; orographic, less rainfall on slope behind peak
  4. Ocean circulation; some coastal areas receive below average rainfall, cold ocean currents (less moisture in air) e.g Humboldt current to S. America

Deserts/drylands = 25-50cm rain/yr

41
Q

How is sediment transported by aeolian processes?

A

Suspension - finest particles, long distance
Saltation - coarser particles, bounce/hop, slower
Creep - large e.g. pebbles, sliding, slowest

42
Q

Give 5 dryland landforms.

A
  1. Desert pavements/rags - loose, fine particles eroded, hard pavement left, erosion limited by coarsening
  2. Ventifacts - eroded rocks sticking out, produced by abrasion by wind
  3. Yardangs - wind abraded ridges oriented with prevailing wind
  4. Inselbergs - isolated mountains of more resistant rock, slowly rounded e.g. Ayers Rock, Australia
  5. Sand seas/Ergs - large sand dunes comprising large regions, induced by changes in wind speeds due to barriers between climate zones
43
Q

What are the 4 types of sand dunes? What are they controlled by?

A

Sand supply, wind regime and vegetation:
1. Barchans - crescentic, ‘horns’ facing away from prevailing wind; sand supply LIMITED, wind is STRONG

  1. Transverse - wavy ridges when barchans merge, perpendicular to winds; sand rich, strong winds
  2. Parabolic - also crescentic, upwind pointing horns, coastal areas, abundant sand and wind plus vegetation
  3. Longitudinal - ‘seif’, long straight ridges parallel to prevailing winds, sand supply moderate/low, strong steady winds
44
Q

How does vegetation affect the hydrological cycle and therefore affect rivers? What are arroyos and Ephemeral Rivers (influenced by veg)? Why was Mars studied in this context?

A

Veg reduces channel width, forces thalweg regions to link

  1. Colonisation, bars at high flow
  2. Prevents sig. floodplain flow
  3. Slows bank erosion

Human activity is altering vegetation e.g. compaction, agricultural, deforestation…

Ephemeral Rivers - lack of veg, thin, impermeable soils, rapid runoff = braided

Arroyos - deep channels, semi-arid, incision, driven changes in veg.

Mars: no vegetation, are there specific landforms associated with veg?

45
Q

Define catastrophism, uniformitarianism and gradualism. What dominates today’s approach?

A

Catastrophism - many landforms are a product of extreme events
Uniformitarianism - ‘the present is the key to the past’
Gradualism - ‘the Earth has evolved slowly over a very long period of time’

Today’s approach is more inclined towards uniformitarianism? At least, it has moved away from catstrophism…

46
Q

Significance of megafloods, earthquakes and volcanic events?

A

Frequency-magnitude concept - which events do most geomorphic work?
Small or large events causing the most change to a landscape?
Megafloods e.g. Missoula (1.10(6) m3/s)
Earthquakes e.g. Chi-Chi, Taiwan, 1999
Volcanic events e.g. Mt St Helens, 1980

47
Q

How do climate cycles and glacial cycles affect landscapes?

A

Ice volume, sea level, isostatic response and local precipitation and vegetation…

48
Q

What are hydrological processes driven by?

A

Changes in climate & veg

49
Q

Significance of river terraces and knick points?

A

Evidence of incision, changing erosion etc.

GEO1213: Earth System Science: Our Changing Planet (4 decks)

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