Modelling of surface to basal hydrology across the Russell Glacier Catchment

Transcription

1 Modelling of surface to basal hydrology across the Russell Glacier Catchment Sam GAP Modelling Workshop, Toronto November 2010

2 Collaborators Alun Hubbard Centre for Glaciology Institute of Geography and Earth Sciences Aberystwyth University, UK Gwenn E. Flowers Department of Earth Sciences Simon Fraser University BC, Canada Christian Schoof Earth and Ocean Sciences University of British Columbia BC, Canada

3 Hydrology Ice dynamics Interactions Effective pressure at the ice-bed interface governs glacier sliding The non-linear relationship between surface meltwater and glacier speedup is not credibly captured by current models This is needed to reduce uncertainties in glacier and ice sheet contributions to sea level Effective pressure also acts at the groundwater exchange

4 Hydrology Ice dynamics Interactions Effective pressure at the ice-bed interface governs glacier sliding The non-linear relationship between surface meltwater and glacier speedup is not credibly captured by current models This is needed to reduce uncertainties in glacier and ice sheet contributions to sea level Effective pressure also acts at the groundwater exchange

5 Hydrology Ice dynamics Interactions Effective pressure at the ice-bed interface governs glacier sliding The non-linear relationship between surface meltwater and glacier speedup is not credibly captured by current models This is needed to reduce uncertainties in glacier and ice sheet contributions to sea level Effective pressure also acts at the groundwater exchange

6 Hydrology Ice dynamics Interactions Effective pressure at the ice-bed interface governs glacier sliding The non-linear relationship between surface meltwater and glacier speedup is not credibly captured by current models This is needed to reduce uncertainties in glacier and ice sheet contributions to sea level Effective pressure also acts at the groundwater exchange

7 Hydrology Ice dynamics Interactions Effective pressure at the ice-bed interface governs glacier sliding The non-linear relationship between surface meltwater and glacier speedup is not credibly captured by current models This is needed to reduce uncertainties in glacier and ice sheet contributions to sea level Effective pressure also acts at the groundwater exchange

8 Ice-flow Model ( et al., JGR, 2010) Higher-order stresses: 1st-order approximation of the Stokes equation (Blatter, 1995; Pattyn, 2002), includes longitudinal stress gradients Flow-band: 2-D flowline model with flow-unit width parameter Lateral Drag: lateral shear stress parameterization, includes sliding at the side walls and glacier basin shape Coulomb friction law: basal sliding rule (Schoof, 2005)

9 Ice-flow Model ( et al., JGR, 2010) Higher-order stresses: 1st-order approximation of the Stokes equation (Blatter, 1995; Pattyn, 2002), includes longitudinal stress gradients Flow-band: 2-D flowline model with flow-unit width parameter Lateral Drag: lateral shear stress parameterization, includes sliding at the side walls and glacier basin shape Coulomb friction law: basal sliding rule (Schoof, 2005)

10 Ice-flow Model ( et al., JGR, 2010) Higher-order stresses: 1st-order approximation of the Stokes equation (Blatter, 1995; Pattyn, 2002), includes longitudinal stress gradients Flow-band: 2-D flowline model with flow-unit width parameter Lateral Drag: lateral shear stress parameterization, includes sliding at the side walls and glacier basin shape Coulomb friction law: basal sliding rule (Schoof, 2005)

11 Ice-flow Model ( et al., JGR, 2010) Higher-order stresses: 1st-order approximation of the Stokes equation (Blatter, 1995; Pattyn, 2002), includes longitudinal stress gradients Flow-band: 2-D flowline model with flow-unit width parameter Lateral Drag: lateral shear stress parameterization, includes sliding at the side walls and glacier basin shape Coulomb friction law: basal sliding rule (Schoof, 2005)

12 Ice-flow Model ( et al., JGR, 2010) Higher-order stresses: 1st-order approximation of the Stokes equation (Blatter, 1995; Pattyn, 2002), includes longitudinal stress gradients Flow-band: 2-D flowline model with flow-unit width parameter Lateral Drag: lateral shear stress parameterization, includes sliding at the side walls and glacier basin shape Coulomb friction law: basal sliding rule (Schoof, 2005)

13 Subglacial Model ( & Flowers, Proc. R. Soc. A, 2010) A mixed subglacial drainage network which includes dynamic switching between drainage components (Flowers, 2008) Distributed - macroporous water sheet - low capacity and efficiency - characteristic of winter Channelized - ice-walled conduits - high capacity and efficiency - characteristic of summer Uplift - When large amounts of water impinge on the glacier bed high water pressures are generated and cause flexure of the overlying ice - This uplift effect is modelled by treating the glacier as a uniform static beam

14 Subglacial Model ( & Flowers, Proc. R. Soc. A, 2010) A mixed subglacial drainage network which includes dynamic switching between drainage components (Flowers, 2008) Distributed - macroporous water sheet - low capacity and efficiency - characteristic of winter Channelized - ice-walled conduits - high capacity and efficiency - characteristic of summer Uplift - When large amounts of water impinge on the glacier bed high water pressures are generated and cause flexure of the overlying ice - This uplift effect is modelled by treating the glacier as a uniform static beam

15 Subglacial Model ( & Flowers, Proc. R. Soc. A, 2010) A mixed subglacial drainage network which includes dynamic switching between drainage components (Flowers, 2008) Distributed - macroporous water sheet - low capacity and efficiency - characteristic of winter Channelized - ice-walled conduits - high capacity and efficiency - characteristic of summer Uplift - When large amounts of water impinge on the glacier bed high water pressures are generated and cause flexure of the overlying ice - This uplift effect is modelled by treating the glacier as a uniform static beam

16 Subglacial Model ( & Flowers, Proc. R. Soc. A, 2010) A mixed subglacial drainage network which includes dynamic switching between drainage components (Flowers, 2008) Distributed - macroporous water sheet - low capacity and efficiency - characteristic of winter Channelized - ice-walled conduits - high capacity and efficiency - characteristic of summer Uplift - When large amounts of water impinge on the glacier bed high water pressures are generated and cause flexure of the overlying ice - This uplift effect is modelled by treating the glacier as a uniform static beam

17 Subglacial Hydrology Model Image taken from Creyts & Clarke, J. Geophys. Res., 2010

18 Image taken from Flowers, Hydrol. Process., 2008

19 Q N u b Q > Q Q N u b Graph taken from Hewitt & Fowler, Hydrol. Process., 2008

20 A Test Case An idealized mountain glacier

21 Sheet discharge, m 3 s Conduit discharge, m 3 s Time, days Time, days Distance downglacier, km Distance downglacier, km 0

22 Time, days Conduit cross-sectional area, m Distance downglacier, km Subglacial water pressure, flotation fraction 240 Time, days Distance downglacier, km

23 240 Basal speed, m a 1 50 Basal shear stress, k Pa Time, days Time, days Distance downglacier, km Distance downglacier, km

24 Time, days Basal longitudinal stress, k Pa Distance downglacier, km 0 Time, days Vertical uplift, cm Distance downglacier, km

25 Comments Model captures seasonal and diurnal cycles as well as the spring-transition Such features have been well observed in Alpine glacier system (e.g. Haut Glacier d Arolla) Increasing evidence of similar behaviour on Arctic glaciers, including Russell (e.g. Bartholomew, 2010) Suggesting a unified treatment of basal processes across a range of scales

26 Comments Model captures seasonal and diurnal cycles as well as the spring-transition Such features have been well observed in Alpine glacier system (e.g. Haut Glacier d Arolla) Increasing evidence of similar behaviour on Arctic glaciers, including Russell (e.g. Bartholomew, 2010) Suggesting a unified treatment of basal processes across a range of scales

27 Comments Model captures seasonal and diurnal cycles as well as the spring-transition Such features have been well observed in Alpine glacier system (e.g. Haut Glacier d Arolla) Increasing evidence of similar behaviour on Arctic glaciers, including Russell (e.g. Bartholomew, 2010) Suggesting a unified treatment of basal processes across a range of scales

28 Comments Model captures seasonal and diurnal cycles as well as the spring-transition Such features have been well observed in Alpine glacier system (e.g. Haut Glacier d Arolla) Increasing evidence of similar behaviour on Arctic glaciers, including Russell (e.g. Bartholomew, 2010) Suggesting a unified treatment of basal processes across a range of scales

29 Comments Model captures seasonal and diurnal cycles as well as the spring-transition Such features have been well observed in Alpine glacier system (e.g. Haut Glacier d Arolla) Increasing evidence of similar behaviour on Arctic glaciers, including Russell (e.g. Bartholomew, 2010) Suggesting a unified treatment of basal processes across a range of scales

30 Subglacial Floods Supraglacial Lake Drainage Event Das et al. Science, 2008 Supraglacial lake of volume km3 Drains through 980 m of ice in 1.4 h 1.2 m of vertical uplift and 0.8 m of horizontal displacement Rapid response followed by subsidence and deceleration over 24 hrs Supraglacial lake on Belcher Glacier, Devon Island Ice Cap. Photo by A. Garner.

31

32 ( a) 24 Time, hr Q s m 3 s (b ) Time, hr Q c m 3 s 1 > (c) Time, hr P w s P w/pi s > Time, hr Distance downglacier, km (d ) 24 (g) Time, hr Distance downglacier, km S τ b m 2 k Pa Distance downglacier, km Time, hr D istance downglacier, km ( e) ω 24 (h ) Time, hr Distance d ownglacier, km σ xx m k Pa D istance downglacier, km ( f ) Time, hr ( i) Time, hr Distance d ownglacier, km D istance downglacier, km u b σ x y m a 1 k Pa Distance d ownglacier, km 100

33 Comments Pre-existing channel network needed to dissipate flood response as quickly as observed Regular seasonal melt as well as lake tapping events condition subglacial system Model limitations - multi-directional flow of flood water Other processes - horizontal turbulent hydraulic fracture for basal crack propagation (Tsai & Rice, JGR, 2010) Supraglacial lake drainage events a regular occurrence within the Russell Glacier Catchment

34 Comments Pre-existing channel network needed to dissipate flood response as quickly as observed Regular seasonal melt as well as lake tapping events condition subglacial system Model limitations - multi-directional flow of flood water Other processes - horizontal turbulent hydraulic fracture for basal crack propagation (Tsai & Rice, JGR, 2010) Supraglacial lake drainage events a regular occurrence within the Russell Glacier Catchment

35 Comments Pre-existing channel network needed to dissipate flood response as quickly as observed Regular seasonal melt as well as lake tapping events condition subglacial system Model limitations - multi-directional flow of flood water Other processes - horizontal turbulent hydraulic fracture for basal crack propagation (Tsai & Rice, JGR, 2010) Supraglacial lake drainage events a regular occurrence within the Russell Glacier Catchment

36 Comments Pre-existing channel network needed to dissipate flood response as quickly as observed Regular seasonal melt as well as lake tapping events condition subglacial system Model limitations - multi-directional flow of flood water Other processes - horizontal turbulent hydraulic fracture for basal crack propagation (Tsai & Rice, JGR, 2010) Supraglacial lake drainage events a regular occurrence within the Russell Glacier Catchment

37 Comments Pre-existing channel network needed to dissipate flood response as quickly as observed Regular seasonal melt as well as lake tapping events condition subglacial system Model limitations - multi-directional flow of flood water Other processes - horizontal turbulent hydraulic fracture for basal crack propagation (Tsai & Rice, JGR, 2010) Supraglacial lake drainage events a regular occurrence within the Russell Glacier Catchment

38 Comments Pre-existing channel network needed to dissipate flood response as quickly as observed Regular seasonal melt as well as lake tapping events condition subglacial system Model limitations - multi-directional flow of flood water Other processes - horizontal turbulent hydraulic fracture for basal crack propagation (Tsai & Rice, JGR, 2010) Supraglacial lake drainage events a regular occurrence within the Russell Glacier Catchment

39 Russell Glacier Catchment Modelling Numerical Model - Ice Dynamics - Basal Sliding - Subglacial Hydrology - Other Hydrology Components

40 Ice Dynamics Model (Pattyn, 2008) A 3-D transient higher-order/full-stokes ice-flow model Image taken from Frank Pattyn s homepage

41 Basal Sliding ( ) u 1/n b τ b = C u b + N n N, Λ = λ maxa Λ m max The hydrology will be coupled to the ice mechanics by use of a Coulomb friction law (Schoof, 2005) This is a pressure dependent sliding rule utilizing the spatial and temporal variations in basal water pressure from the hydrology model Overcomes problem of standard sliding laws that allow arbitrarily large basal shear stresses regardless of effective pressure Implemented as a non-linear Robin-type boundary condition which cannot be solved independently but forms part of the solution to the ice-flow problem

42 Basal Sliding ( ) u 1/n b τ b = C u b + N n N, Λ = λ maxa Λ m max The hydrology will be coupled to the ice mechanics by use of a Coulomb friction law (Schoof, 2005) This is a pressure dependent sliding rule utilizing the spatial and temporal variations in basal water pressure from the hydrology model Overcomes problem of standard sliding laws that allow arbitrarily large basal shear stresses regardless of effective pressure Implemented as a non-linear Robin-type boundary condition which cannot be solved independently but forms part of the solution to the ice-flow problem

43 Basal Sliding ( ) u 1/n b τ b = C u b + N n N, Λ = λ maxa Λ m max The hydrology will be coupled to the ice mechanics by use of a Coulomb friction law (Schoof, 2005) This is a pressure dependent sliding rule utilizing the spatial and temporal variations in basal water pressure from the hydrology model Overcomes problem of standard sliding laws that allow arbitrarily large basal shear stresses regardless of effective pressure Implemented as a non-linear Robin-type boundary condition which cannot be solved independently but forms part of the solution to the ice-flow problem

44 Basal Sliding ( ) u 1/n b τ b = C u b + N n N, Λ = λ maxa Λ m max The hydrology will be coupled to the ice mechanics by use of a Coulomb friction law (Schoof, 2005) This is a pressure dependent sliding rule utilizing the spatial and temporal variations in basal water pressure from the hydrology model Overcomes problem of standard sliding laws that allow arbitrarily large basal shear stresses regardless of effective pressure Implemented as a non-linear Robin-type boundary condition which cannot be solved independently but forms part of the solution to the ice-flow problem

45 Subglacial Model (Schoof, Nature, 2010) - A unified treatment of linked cavities and channels - 2-D planform network of conduits - Switching between drainage components within a spatially extended drainage catchment S ij t S Q = c 3 S α Ψ 1/2 Ψ N = P i P w Ψ = ρ w g b = c 1 Q ij Ψ ij + u b h c 2 N n ij S ij s Pw s u b h c 1, c 2, c 3, α conduit cross-sectional area water discharge effective pressure hydraulic gradient basal sliding speed bedrock bump constants

46 Images taken from Schoof, Nature, 2010

47 Other Hydrology Components Supraglacial hydrology Englacial storage and transport Groundwater flow Image taken from Flowers, Hydrol. Process., 2008

48 Data - Surface and Bed Topography (DEM) - Automatic Weather Station (AWS) data used to obtain spatial and temporal melt variability - Surface Velocities - from kgps and remotely-sensed observations - Basal reflectance - indicators of stick-slip zones - Seismics - to ascertain bed properties - Observations of englacial storage and surface-to-bed transition times - Supraglacial lake/moulin locations, volumes and drainage times

49 Research Objectives Glacier catchment response to variable inputs of melt (seasonal, diurnal and lake tapping events) Influence of englacial storage and surface-to-bed transition times How does ice-flow and subglacial processes interact to produce temporal and spatial patterns in basal decoupling Dynamic response to basal boundary layer stress distribution Compare 2009 and 2010 melt seasons Russell glacier catchment under future climate projections

50 Research Objectives Glacier catchment response to variable inputs of melt (seasonal, diurnal and lake tapping events) Influence of englacial storage and surface-to-bed transition times How does ice-flow and subglacial processes interact to produce temporal and spatial patterns in basal decoupling Dynamic response to basal boundary layer stress distribution Compare 2009 and 2010 melt seasons Russell glacier catchment under future climate projections

51 Research Objectives Glacier catchment response to variable inputs of melt (seasonal, diurnal and lake tapping events) Influence of englacial storage and surface-to-bed transition times How does ice-flow and subglacial processes interact to produce temporal and spatial patterns in basal decoupling Dynamic response to basal boundary layer stress distribution Compare 2009 and 2010 melt seasons Russell glacier catchment under future climate projections

52 Research Objectives Glacier catchment response to variable inputs of melt (seasonal, diurnal and lake tapping events) Influence of englacial storage and surface-to-bed transition times How does ice-flow and subglacial processes interact to produce temporal and spatial patterns in basal decoupling Dynamic response to basal boundary layer stress distribution Compare 2009 and 2010 melt seasons Russell glacier catchment under future climate projections

53 Research Objectives Glacier catchment response to variable inputs of melt (seasonal, diurnal and lake tapping events) Influence of englacial storage and surface-to-bed transition times How does ice-flow and subglacial processes interact to produce temporal and spatial patterns in basal decoupling Dynamic response to basal boundary layer stress distribution Compare 2009 and 2010 melt seasons Russell glacier catchment under future climate projections

54 Research Objectives Glacier catchment response to variable inputs of melt (seasonal, diurnal and lake tapping events) Influence of englacial storage and surface-to-bed transition times How does ice-flow and subglacial processes interact to produce temporal and spatial patterns in basal decoupling Dynamic response to basal boundary layer stress distribution Compare 2009 and 2010 melt seasons Russell glacier catchment under future climate projections

55 Research Objectives Glacier catchment response to variable inputs of melt (seasonal, diurnal and lake tapping events) Influence of englacial storage and surface-to-bed transition times How does ice-flow and subglacial processes interact to produce temporal and spatial patterns in basal decoupling Dynamic response to basal boundary layer stress distribution Compare 2009 and 2010 melt seasons Russell glacier catchment under future climate projections

56 Questions?