Refs Flashcards
Zwally et al (2002)
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
Shepherd et al (2009)
‘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
glacier velocity is proportional to number of PDDs due to basal melt = lubrication = enhanced basal sliding
Zwally et al (2002)
‘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
Shepherd et al (2009)
Shepherd 2009 and Zwally 2002 (overarching idea)
more PDD = faster flow
more PDD = faster flow (2 main proponents)
Shepherd 2009 and Zwally 2002
Schoof (2010)
(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)
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)
Schoof (2010)
Controls on ice V
basal sliding, shear stress of underlying deformable sediments and strain (aka internal deformation)
Stress (t) proportional to:
ice thickness, slope gradient, density of ice, gravitational constant
strain =
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
what drives water flow
hydraulic pressure= elevation head + pressure head
Shreves (1972)
theory of englacial conduits = wp in englacial conduit = ice overburden pressure –> steady state
Braithwaite and Olesen
PDDs = quality indicator of ablation–> this assumption used by Zwally 2002
PDDs = quality indicator of ablation–> this assumption used by Zwally 2002
Braithwaite and Olesen
Thomsen
MW flows straight from moulin to the base
Iken et al (1983)
uplift- glacier lifted 0.6m due to summer WP and V increased 3-6 times
uplift- glacier lifted 0.6m due to summer WP and V increased 3-6 times
Iken et al (1983)
Sundal 2011
- -> 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
- -> 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
Sundal 2011
Price 2008
- ->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
- ->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
Price 2008
Van de Waal 2008
17 year deceleration rate in ice flow along k transect of GrIS during a period of increased melt
Palmer 2015
GrIS subglacial lake outbursts can induce rapid acceleration
–> short term spikes in water (Schoof, 2010) = faster flow
GrIS subglacial lake outbursts can induce rapid acceleration
–> short term spikes in water (Schoof, 2010) = faster flow
Palmer 2015
Röthlisberger 1972
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
Hallet 1979
water films
Hart 2019
‘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
Stearns 2008
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)
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)
Stearns 2008
‘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
Hart 2019
Alley and Anadakris 1997
stagnation of ice stream C in west antarctica due to sticky spots
stagnation of ice stream C in west antarctica due to sticky spots
Alley and Anadakris 1997
Bartholomew 2012
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
Das 2008
hydrofracture can aid water to base and is synchronous with uplift
