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Hydrology > Refs > Flashcards

Refs Flashcards

1
Q

Zwally et al (2002)

A

glacier velocity is proportional to number of PDDs due to basal melt = lubrication = enhanced basal sliding

  • -> mid winter average = 32.8cm/day
  • -> summers of 1998 and 1999 = 40.1 and 38.1cm/day= coincided with very warm summers
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2
Q

Shepherd et al (2009)

A

‘ice jacking’ can occur if supraglacial MW is drained to ice-bed interface by moulins–> water pressure lowers ENP = jacking so less friction
–> Greenland diurnal variations
–> coincident fluctuations in ice melt, elevation and velocity
–> 4cm a day –> 2 hour lag shown in graph between peak temp +jacking and peak melt for 1km thick ice
plausible time for drainage

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3
Q

glacier velocity is proportional to number of PDDs due to basal melt = lubrication = enhanced basal sliding

A

Zwally et al (2002)

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4
Q

‘ice jacking’ can occur if supraglacial MW is drained to ice-bed interface by moulins–> water pressure lowers ENP = jacking so less friction
–> Greenland diurnal variations
–> coincident fluctuations in ice melt, elevation and velocity
–> 4cm a day –> 2 hour lag shown in graph between peak temp +jacking and peak melt for 1km thick ice
plausible time for drainage

A

Shepherd et al (2009)

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5
Q

Shepherd 2009 and Zwally 2002 (overarching idea)

A

more PDD = faster flow

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6
Q

more PDD = faster flow (2 main proponents)

A

Shepherd 2009 and Zwally 2002

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7
Q

Schoof (2010)

A

(Greenland) transitioning seasonal drainage pathways. Early summer melt will induce acceleration but once critical threshold surpassed (1.4cm/day) = transition from distributed to channelised= more efficient so lower WP= slower

  • -> So ice v responds faster too short term water spikes than long term increased av flow as this causes channelisation
  • -> channelisation occurs due to Röthlisberger (1972) channelisation ideas (wp changes as channels get bigger etc)
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8
Q

transitioning seasonal drainage pathways. Early summer melt will induce acceleration but once critical threshold surpassed (1.4cm/day) = transition from distributed to channelised= more efficient so lower WP= slower
–> So ice v responds faster too short term water spikes than long term increased av flow as this causes channelisation
> channelisation occurs due to Röthlisberger (1972) channelisation ideas (wp changes as channels get bigger etc)

A

Schoof (2010)

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9
Q

Controls on ice V

A

basal sliding, shear stress of underlying deformable sediments and strain (aka internal deformation)

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10
Q

Stress (t) proportional to:

A

ice thickness, slope gradient, density of ice, gravitational constant

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11
Q

strain =

A

follows glenn’s flow law= (stress*temp)^n
deformation occurs once ‘plastic region of deformation’ is surpassed–> higher temp = higher strain = softening of ice–> increases strain for the same stress

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12
Q

what drives water flow

A

hydraulic pressure= elevation head + pressure head

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13
Q

Shreves (1972)

A

theory of englacial conduits = wp in englacial conduit = ice overburden pressure –> steady state

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14
Q

Braithwaite and Olesen

A

PDDs = quality indicator of ablation–> this assumption used by Zwally 2002

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15
Q

PDDs = quality indicator of ablation–> this assumption used by Zwally 2002

A

Braithwaite and Olesen

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16
Q

Thomsen

A

MW flows straight from moulin to the base

17
Q

Iken et al (1983)

A

uplift- glacier lifted 0.6m due to summer WP and V increased 3-6 times

18
Q

uplift- glacier lifted 0.6m due to summer WP and V increased 3-6 times

A

Iken et al (1983)

19
Q

Sundal 2011

A
  • -> transitioning drainage systems once CT 1.4cm/day is passed
  • -> reason for the deceleration of Greenland v despite increased melt
  • -> speed up in second half of melt season = 62% less in warmer years and period of acceleration = 3x shorter
20
Q
  • -> transitioning drainage systems once CT 1.4cm/day is passed
  • -> reason for the deceleration of Greenland v despite increased melt
  • -> speed up in second half of melt season = 62% less in warmer years and period of acceleration = 3x shorter
A

Sundal 2011

21
Q

Price 2008

A
  • ->inward flow propagation of acceleration from 12km closer to margins than Zwally 2002 hyp’d
  • -> ‘ELA-hydrafracture hyp’
  • ->ice is thinner at margins so more prone to hydrofracture= water to base = induced acceleration which propagates upstream
22
Q
  • ->inward flow propagation of acceleration from 12km closer to margins than Zwally 2002 hyp’d
  • -> ‘ELA-hydrafracture hyp’
  • ->ice is thinner at margins so more prone to hydrofracture= water to base = induced acceleration which propagates upstream
A

Price 2008

23
Q

Van de Waal 2008

A

17 year deceleration rate in ice flow along k transect of GrIS during a period of increased melt

24
Q

Palmer 2015

A

GrIS subglacial lake outbursts can induce rapid acceleration
–> short term spikes in water (Schoof, 2010) = faster flow

25
Q

GrIS subglacial lake outbursts can induce rapid acceleration
–> short term spikes in water (Schoof, 2010) = faster flow

A

Palmer 2015

26
Q

Röthlisberger 1972

A

channelised drainage theory

  • -> steady state: channel melt vs creep closure
  • -> melt increases as water influx increases so channel is bigger = lower wp = draws water in = channels created
27
Q

Hallet 1979

A

water films

28
Q

Hart 2019

A

‘stick-slip motion’

  • -> 2 dif styles of glacier motion
  • -> long phases of slow movement interrupted by episodic bursts
  • -> slip = rapid sliding associated with ice quakes + low enp
29
Q

Stearns 2008

A

subglacial floods in east antarctica- byrd glacier

–> 10% increase in v at byrd glacier in 2005-07 coincided with drainage of 2 large subglacial lakes (1.7km^3)

30
Q

subglacial floods in east antarctica- byrd glacier

–> 10% increase in v at byrd glacier in 2005-07 coincided with drainage of 2 large subglacial lakes (1.7km^3)

A

Stearns 2008

31
Q

‘stick-slip motion’

  • -> 2 dif styles of glacier motion
  • -> long phases of slow movement interrupted by episodic bursts
  • -> slip = rapid sliding associated with ice quakes + low enp
A

Hart 2019

32
Q

Alley and Anadakris 1997

A

stagnation of ice stream C in west antarctica due to sticky spots

33
Q

stagnation of ice stream C in west antarctica due to sticky spots

A

Alley and Anadakris 1997

34
Q

Bartholomew 2012

A

diurnal v variability in greenland
v increased at sites 2,3,4 by 50-300m/yr on daily cycles
followed pattern of temp peaks and showed a lag of 2-4hours

35
Q

Das 2008

A

hydrofracture can aid water to base and is synchronous with uplift

Hydrology (2 decks)

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