glacier hydrology ice -directed drainage isdirigert drenering supraglacial lateral englacial...
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Glacier hydrology Ice -directed drainageIsdirigert drenering
• Supraglacial• Lateral • Englacial• Subglacial
Supraglacial drainage - Kongsvegen, Svalbard
Superimposed ice forming
Department of geosciences
Mother earth is crying
Krabill et al. 2000
Why do the glaciers Why do the glaciers accelerate ?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
Department of geosciences2000 2100
Future runoff from small glaciers Future runoff from small glaciers
and ice capsand ice caps
Summer discharge curves - Bayelva
Four years of daily runoff in Bayelva
0
2
4
6
8
10
12
14
1 9 17 25 33 41 49 57 65 73 81 89 97 105 113 121 129
Days
Dis
char
ge
(m3/
s)
Water through-flow
• Response curves
• Water flow velocity:
v ≥ 0,40 m/s
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-channelcanal
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
Darcy’s flow law
Fluid flow of fluid through a porous media
where κ is permeability and μ viscosity
Subglacial drainage in quiescent stage tunnel system (R-channels) pw low and decrease
with Q
(Hock & Hooke 1993)
Non-deformable bed: High flux hydraulics
Photo: Michael Hambrey
R-channels: Melt enlargement and creep closure in competition
Flowing water generates heatChannel enlargement into the ice
Creep closure due to deformable ice
Seasonal and diurnal geometry evolution
Steady-state:
inverse pressure-discharge relation
arborescent structure
low surface-to-volume ratio
courtesy: U.H. Fischer
Subglacial drainage during surge– linked cavity - pw is high and increase with Q
(Kamb 1987)
(Cavity)
Links
Institute of geosciences
Engabreen
Engabreen – subglacial tunnel system
Bondhusbreen, Folgefonna
Bondhusbreen - Folgefonna
Bondhusbreen
Bondhusbreen - Folgefonna
Department of geosciences
Department of geosciences
Deformation rate h = 160mGlens flow law: ė = A τⁿClosure rate: dr/dt = A (P/n)ⁿ
dr/dt ~ 100-150 mm/dIf P = ρgh = 14 bar, n = 3:
A = 0.36 y-1 bar-1
or 11.4 * 10-15 s-1kPa-3
- twice as high as Peterson
Ice deformation
Ice deformation
Institute of geosciences
Engabreen – subglacial laboratory
Kamb, 1987
Non-deformable bed: Low flux hydraulicsLinked-cavity system
Nigardsbreen still advanced in 2004
Glaciers on deformable and non-deformable beds
Deformable bed Non-deformable bed
Bed displacementSliding, deformation, free-slip
HydraulicsDarcian flow, canals and R-channels
HydraulicsLinked cavities and R-channels
Bed displacementSliding
Landformsstreamlined forms (drumlins)
LandformsRoches moutonnées, U-valleys
pi
pw
Non-deformable bed: Low flux hydraulics
Glacier dammed lakes - Vatnajökull – Iceland
Glacier dammed lake during a surge at Usherbreen, Svalbard
Glacier dammed lake – Glacier dammed lake – BlåmannsisenBlåmannsisen(fra R. Engeset, NVE)
Water level in lake
Discharge from lake
Water level in reservoir
Hubbard glacier surge – glacier dammed fjord
Hubbard glacier surge – glacier dammed fjord
Subglacial lake – Grimsvötn, Vatnajökull, Iceland
Subglacial lakes – stable -unstable
Moraine dammed lake – potential GLOF
Ice directed drainage Some equations:
Ice overburden pressure
Flotation level
Effective pressure
Fluid potential
Potential gradient
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:
s
gh) ( k +
s
)zg ( = ibw
b
Subglacial lakes in Antarctica
Location of observed lakes
Lake Vostok
(from Clarke, 2006)