1. Glacier hydrology Ice -directed drainage Isdirigert drenering
Supraglacial
Lateral
Englacial
Subglacial

2. Supraglacial drainage - Kongsvegen, Svalbard

9. Superimposed ice forming

10. Mother earth
is crying

11. Why do the glaciers accelerate ?
Increased basal sliding:
1. More surface meltwater lubricate the bed
2. Less backpressure – calving and bottom melting under the floating ice
3. Sea water temperature and circulation
Krabill et al. 2000

12. Future runoff from small glaciers and ice caps
2000
2100

14. Summer discharge curves - Bayelva

15. Water through-flow
Response curves
Water flow velocity:
v ≥ 0,40 m/s

16. Deformable bed: Darcian flow, canals and R-channels
Thin sediment layers can not transport large fluxes of water
the drainage capacity will be exceeded by the water supply
water will start flowing along the ice-till interface
R-channel
canal
For small surface slopes (<0.1)
water will drain in canals of high water pressure eroded into the sediments
For large surface slopes (>0.1)
water will drain in R-channels eroded into the ice
Darcian flow: Follow the hydraulic gradient within the till
Well sorted (grains of approximately all one size) materials have higher porosity than similarly sized poorly sorted materials (where smaller particles fill the gaps between larger particles).
Consolidation takes place when a normal force is applied to the till.
But since the till is water saturated, and water is incompressible, two outcomes are possible:
First; if the water is free to drain, then fine. The soil will consolidate and the porosity decrease.
Secondly, if the water is unable to drain or the conductivity is to small, the pore water pressure will increase. Increasing the pore water pressure means weakening the soil. I will explain more about this in a minute.
A dilatant material is one in which viscosity increases with the rate of shear (also termed shear thickening).
Finally, if now the ice on top of the till increases its speed, the saturated till can start shearing. Due to its inhomogeneity, the soil will increase its volume –> increasing its pore volume -> decreasing its pore pressure or increase its water volume. If the pore water pressure is reduced, the soil increases its yield strength, whereas if the water volume increases the soil becomes weaker than it was before shear deformation commenced
Dilatancy - The mean of measured porosity for sediments underlying active Whillans and Bindschadler ice streams in West Antarctica lies in the range 0.40≤ n≤ 0.48 (Kamb 2001); such high values imply that these sediments are dilated.
Because soils compress more readily than they decompress, there is a strong tendency for soils to reduce their pore volume when they are subjected to cycles of loading and unloading. Dilatancy is the only subglacial mechanical process that can greatly increase porosity and, in doing so, erase the memory of loading history that is encoded in the overconsolidation poc of the sediment.
The different drainage systems influence the way glaciers move over their bed.
We will now see how variable effective pressures changes the surface velocity of glaciers

17. Darcy’s flow law Fluid flow of fluid through a porous media
where κ is permeability and μ viscosity

18. Subglacial drainage in quiescent stage tunnel system (R-channels) pw low and decrease with Q
(Hock & Hooke 1993)

19. Non-deformable bed: High flux hydraulics
R-channels: Melt enlargement and creep closure in competition
Flowing water generates heat
Channel enlargement into the ice
Creep closure due to deformable ice
Seasonal and diurnal geometry evolution
Photo: Michael Hambrey
courtesy: U.H. Fischer
Steady-state:
inverse pressure-discharge relation
arborescent structure
low surface-to-volume ratio

20. Subglacial drainage during surge– linked cavity - pw is high and increase with Q
Links
(Kamb 1987)

21. Engabreen

22. Engabreen – subglacial tunnel system

23. Bondhusbreen, Folgefonna

24. Bondhusbreen - Folgefonna

27. Deformation rate h = 160m
Glens flow law: ė = A τⁿ Closure rate: dr/dt = A (P/n)ⁿ dr/dt ~ mm/d If P = ρgh = 14 bar, n = 3: A = 0.36 y-1 bar-1 or 11.4 * s-1kPa-3 - twice as high as Peterson

28. Ice deformation

29. Ice deformation

30. Engabreen – subglacial laboratory

31. Non-deformable bed: Low flux hydraulics Linked-cavity system
Since the two systems discussed here
Kamb, 1987

32. Nigardsbreen still advanced in 2004

33. Glaciers on deformable and non-deformable beds
Hydraulics
Darcian flow, canals and R-channels
Hydraulics
Linked cavities and R-channels
So, now we have come to the core of this talk.
I will focus on the processes that take place underneath glaciers that are underlain by deformable beds consisting of soft sediments, and contrast these with the processes that works underneath glaciers that are underlain by non-deformable beds as bedrock.
A deformable bed consists of till. Till is a non-sorted material typical for glaciers.
A non-deformable bed has no sediments between the basal ice and the bed.
Both valley glaciers and ice sheets can rest on both kind of beds.
Ice streams and surging glaciers have so far only been found on deformable beds.
Bed displacement
Sliding, deformation, free-slip
Bed displacement
Sliding
Landforms
streamlined forms (drumlins)
Landforms
Roches moutonnées, U-valleys

34. Non-deformable bed: Low flux hydraulicspi pw

35. Glacier dammed lakes - Vatnajökull – Iceland

36. Glacier dammed lake during a surge at Usherbreen, Svalbard

38. Glacier dammed lake – Blåmannsisen (fra R. Engeset, NVE)

42. Water level in lake
Discharge from lake
Water level in reservoir

44. Hubbard glacier surge – glacier dammed fjord

45. Hubbard glacier surge – glacier dammed fjord

46. Subglacial lake – Grimsvötn, Vatnajökull, Iceland

47. Subglacial lakes – stable -unstable

48. Moraine dammed lake – potential GLOF

49. Ice directed drainage Some equations: Ice overburden pressure
Flotation level
Effective pressure
Fluid potential
Potential gradient

50. Water pressure potential
In one point: Φb= ρw g Zb+ Pw
where Pw is the subglacial water pressure Pw= k ρi g hi
where hi = Zs – Zb and k є [0, 1]
Driving force – the potential difference:

52. Subglacial lakes in Antarctica

53. Location of observed lakes

57. Lake Vostok

60. (from Clarke, 2006)