Lecture 2 - water in glaciers

Question 1

Bjornsson (1992)

Answer 1

Jokulhaups in Iceland

• daring regularly from 6 subG areas in Iceland
• occur when lake reaches a critical level, could predict when they’re about to occur
• sudden drainage: leads to unstable growth of subG water conduits

flowing water not confined to a tunnel, spread out beneath the G - later gradually collects back in conduits

large floods - ice dam is broken and water flows over it
smaller floods - drains through subG tunnels, so have longer duration

Question 2

Bjornsson (1992) jokulhaulps origin and effects

Answer 2

3 origins:

• subG lakes at geothermal areas (heats and melts the G bed and melt becomes trapped in a lake at the bed, seal brakes and lake drains)
• meltwater drained during volcanic eruptions (hyper concentrated fluid-sediment mixtures)
• marginal ice dammed lakes (more frequent but smaller volume than in the past, due to thinning of ice dams)

effects
- transport and deposition of sediments over outwash planes

Question 3

Holmlund (1988)

Answer 3

Moulins, Sweden

Moulins require: crevasses and a supply of meltwater, to form
- therefore needs to be in places with high extending strain rate (to form crevasses)

crevasses may cross cut streams

crevasses may be deep enough that they reach depths where the glacier is at the PMP

moraine trains - where new moulins form up glacier - new crevasses intersect the meltwater stream

water lower albedo than snow

Question 4

Holmlund (1988) formation of moulins

Answer 4

as crevasse deepens, may intersect enG channel - water can then drain through this

heat from MW helps to keep the connection open and hence formation of a moulin

englacial channel enlarges rapidly by melting - utilising mechanic energy released by the descending water

stepped moulins my form but vertical more common

complicated network of channels below moulins

Question 5

Gulley and Benn (2009)

Answer 5

conduits

recharge points are concentrated at a few discrete processes

efficient enG drainage systems traverse great thicknesses of impermeable cold ice

water flow through conduits melts the walls by viscous heat dissipation: large conduits have greater discharge and dissipate more heat per unit wall area

in debris filled crevasse traces, water enlarges a passage, then positive feedback between discharge and passage size eventually creates a conduit

presence of water in crevasses, alters force balance, presses out on walls and counters the overburden pressure

Question 6

Zwalley et al (2002)

Answer 6

ice sheet motion: ice deformation, basal sliding, or deformation in the till layer

floating glacier tongues/ice shelves - respond quickly to changes in basal heat fluxes and melting

meltwater at base of ice sheet = rapid mechanism for lubricating flow

ice base at PMP - wet base maintained throughout a year

summer acceleration - increase in water pressure at the bedrock interface water can lead to decoupling of the ice from the bed

Question 7

Zwalley et al (2002) surface melting

Answer 7

ice acceleration when surface melting; coupling between surface melting and ice sheet flow
- mechanism for rapid, large scale, dynamic response to ice sheets to climate warming

inter annual variations in ice thickness correlated with variations in surface melting intensity

greenland ablation zone - surface MW runs along surface and collects in surface lakes of flows directly into moulins

Question 8

Sorg et al (2012)

Answer 8

G run off is crucial for water allocation, there have been shifts in seasonal run off maxima

Tien Shan Gs provide important water source for population, increase temps since 1970’s, max snow cover thickness has decreased

G shrinkage is less severe in continental inner ranges than in more humid outer ranges

G’s crucial role in Central Asias hydrological regime, will continue to lose mass in the coming decades

Question 9

Nienow (1998)

Answer 9

Haut glacier d’Arolla seasonal changes in subG drainage system morphology, shown by dye tracing

removal of snow –> dramatic increase in volume run off

induced transient high water pressures within the distributed drainage system causing evolution into rapidly channelized system, developed to have higher velocities with fewer links

surges may be linked to changes in the morphology of subG drainage systems

distributed (multi-thread configuration) –> more efficient, extensive channel system (less threads) which can drain the bulk of supraG derived MW

drainage pathways may shrink and become blocked off using the winter: must reform each melt season

Question 10

Menzies (2002)

Answer 10

(hydrology?) causes channel bed erosion, scour and the development of complex drainage networks within all G environments

G water originates from melting = basal, friction, geothermal heat, air temp, passage of MW over the top

MW discrete segregated hydraulic systems or a few large systems that interconnects with subG environments

Question 11

Fountain and Walder (1998)

Answer 11

porous, permeable firn temporarily stores water

water flux depends on surface melt and rainfall - volume of water stored by G varies diurnally and seasonally

enG conduits = where melt enlargement from energy dissipated from the flowing water can balance the inward creed of ice

outburst floods common for Gs

surging Gs store large volumes of water, surge terminations associated with the release of large volumes of water

crevasses - most important avenue on temperature Gs because there are more of them than moulins