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)