Physics of Glaciers: Glacier Hydraulics

Transcription

1 Introduction Theory Examples References Physics of Glaciers: Glacier Hydraulics Mauro A. Werder VAW / ETHZ

2 Introduction Theory Examples References Problems Front matters Me: postdoc at VAW specialising in subglacial hydraulics/hydrology. I ll give this and next lecture. 1

3 Introduction Theory Examples References Problems Front matters Me: postdoc at VAW specialising in subglacial hydraulics/hydrology. I ll give this and next lecture. There is only some script for these two lectures! Take notes. I ll provide the slides but most content will be on blackboard. 1

4 Introduction Theory Examples References Problems Why study glacier hydraulics? Basal sliding of glacier/ice sheets is dependent on basal water pressure: One possible sliding law: u b = Bτb mn r where N = p i p w e.g. Budd et al. (1979) 2

5 Introduction Theory Examples References Problems Why study glacier hydraulics? Glacier lake outburst floods are one of the greatest and most far reaching glaciological hazards: Gornergletscher & lake 3

6 Introduction Theory Examples References Problems Why study glacier hydraulics? Glacier lake outburst floods are one of the greatest and most far reaching glaciological hazards: Gornergletscher & lake Zermatt

7 Introduction Theory Examples References Problems Why study glacier hydraulics? Landscape evolution and sediment transport: Griesgletscher and dam Photo by Ian Delaney 4

8 Introduction Theory Examples References Problems Case study I: A big glacier flood in Iceland 5

9 Introduction Theory Examples References Problems Case study I: A big glacier flood in Iceland 5

10 Introduction Theory Examples References Problems Case study I: A big glacier flood in Iceland Jökulhlaups (glacier lake outburst floods) often occur in Iceland. The most famous one is the outburst of Grimsvötn, a subglacial lake. (e.g. Björnsson, 2003) 6

11 Introduction Theory Examples References Problems Case study I: A big glacier flood in Iceland Floodplain after the big 1996 flood which destroyed the Iceland s ring-road. 7

12 Introduction Theory Examples References Problems Case study I: A big glacier flood in Iceland What would you want to know about this system? 8

13 Introduction Theory Examples References Problems Case study I: A big glacier flood in Iceland What would you want to know about this system? What physics? What measurements? 8

14 Introduction Theory Examples References Problems Case study II: A glacier s daily routine Measurements from the Greenland Ice Sheet (and also alpine glaciers) show that surface velocity can have a diurnal signal. Andrews et al. (2014) 9

15 Introduction Theory Examples References Problems Case study II: A glacier s daily routine Observations: Using data from Andrews et al. (2014) 10

16 Introduction Theory Examples References Problems Case study II: A glacier s daily routine Observations: Surface velocity has a diurnal signal Using data from Andrews et al. (2014) 10

17 Introduction Theory Examples References Problems Case study II: A glacier s daily routine Observations: Surface velocity has a diurnal signal Surface temperature and thus melt has a diurnal signal Using data from Andrews et al. (2014) 10

18 Introduction Theory Examples References Problems Case study II: A glacier s daily routine Observations: Surface velocity has a diurnal signal Surface temperature and thus melt has a diurnal signal What s going on? What should we measure? Using data from Andrews et al. (2014) 10

19 Introduction Theory Examples References Problems Case study II: A glacier s daily routine If increased water input leads to higher water pressure, then (through a sliding law such as u b = Bτ m b N r ) we can expect higher flow speeds. Using data from Andrews et al. (2014) 11

20 Introduction Theory Examples References Problems Case study II: A glacier s daily routine If increased water input leads to higher water pressure, then (through a sliding law such as u b = Bτ m b N r ) we can expect higher flow speeds. Question: What kind of glacier drainage system produces the observed pressure response? Using data from Andrews et al. (2014) 11

21 Introduction Theory Examples References Theory of glacier hydrology & hydraulics 12

22 Introduction Theory Examples References Theory of glacier hydrology & hydraulics 13

23 Introduction Theory Examples References Water flow through a glacier 14

24 Introduction Theory Examples References Water flow through a glacier 15

25 Introduction Theory Examples References Water flow through a glacier Cross-section of ablation area of glacier/ice sheet 16

26 Introduction Theory Examples References Subglacial drainage system Water flow through a glacier 17

27 Introduction Theory Examples References Englacial drainage system Water flow through a glacier 18

28 Introduction Theory Examples References Subglacial drainage We will focus on subglacial drainage 19

29 Introduction Theory Examples References Subglacial drainage Drainage system type: Distributed/inefficent/slow Channelized/efficient/fast linked cavities canals patchy sheet R-channels Linked cavities: Walder (1986); Kamb (1987) Canals: Walder and Fowler (1994) Patchy: Creyts and Schoof (2009) R-Channels: Röthlisberger (1972); Nye (1976) Spring and Hutter (1982) R-channels + l.-cavities (conduits): Kessler and Anderson (2004); Schoof (2010) 19

30 Introduction Theory Examples References Subglacial drainage Drainage system type: Distributed/inefficent/slow Channelized/efficient/fast linked cavities canals patchy sheet R-channels Linked cavities: Walder (1986); Kamb (1987) Canals: Walder and Fowler (1994) Patchy: Creyts and Schoof (2009) R-Channels: Röthlisberger (1972); Nye (1976) Spring and Hutter (1982) R-channels + l.-cavities (conduits): Kessler and Anderson (2004); Schoof (2010) 19

31 Introduction Theory Examples References Modelling subglacial hydraulics 20

32 Introduction Theory Examples References Hydraulic potential routing Routing the water according to overburden hydraulic potential: Fischer et al. (2005) 21

33 Introduction Theory Examples References Hydraulic potential routing Fischer et al. (2005) 22

34 Introduction Theory Examples References more slides to come... 23

35 Introduction Theory Examples References Additional recommended papers: Jökulhlaup simulations: Clarke (2003) Recent review paper on modelling: Flowers (2015) Closure of cylindrical bore-hole (or channel): Nye (1953) Summer school course in Copenhagen with exercise (the jökulhlaup example): References I Bibliography: Andrews, L. C., Catania, G. A., Hoffman, M. J., Gulley, J. D., Luthi, M. P., Ryser, C., Hawley, R. L., and Neumann, T. A. (2014). Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet. Nature, 514(7520): Björnsson, H. (2003). Subglacial lakes and jökulhlaups in Iceland. Global and Planetary Change, 35(3-4): Budd, W. F., Keage, P. L., and Blundy, N. A. (1979). Empirical studies of ice sliding. Journal of Glaciology, 23(89): Clarke, G. K. C. (2003). Hydraulics of subglacial outburst floods: new insights from the Spring-Hutter formulation. Journal of Glaciology, 49(165): Creyts, T. T. and Schoof, C. G. (2009). Drainage through subglacial water sheets. Journal of Geophysical Research, 114(F4):F doi: /2008jf Fischer, U. H., Braun, A., Bauder, A., and Flowers, G. E. (2005). Changes in geometry and subglacial drainage derived from digital elevation models: Unteraargletscher, Switzerland, Annals of Glaciology, 40: Flowers, G. E. (2015). Modelling water flow under glaciers and ice sheets. Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences, 471(2176). 24

36 Introduction Theory Examples References References II Kamb, B. (1987). Glacier surge mechanism based on linked cavity configuration of the basal water conduit system. Journal of Geophysical Research, 92(B9): Kessler, M. A. and Anderson, R. S. (2004). Testing a numerical glacial hydrological model using spring speed-up events and outburst floods. Geophysical Research Letters, 31(18):L Nye, J. F. (1953). The flow law of ice from measurements in glacier tunnels, laboratory experiments and the Jungfraufirn borehole experiment. Proceedings of the Royal Society of London, Ser. A, 219(1193): Nye, J. F. (1976). Water flow in glaciers: jökulhlaups, tunnels and veins. Journal of Glaciology, 17(76): Röthlisberger, H. (1972). Water pressure in intra- and subglacial channels. Journal of Glaciology, 11(62): Schoof, C. (2010). Ice-sheet acceleration driven by melt supply variability. Nature, 468(7325): Spring, U. and Hutter, K. (1982). Conduit flow of a fluid through its solid phase and its application to intraglacial channel flow. International Journal of Engineering Sciences, 20: Walder, J. S. (1986). Hydraulics of subglacial cavities. Journal of Glaciology, 32(112): Walder, J. S. and Fowler, A. (1994). Channelized subglacial drainage over a deformable bed. Journal of Glaciology, 40(134):