Glacier Hydrology. Why should you care?

Transcription

1 Glacier Hydrology Why should you care?

2 Climate Local Meteorology Surface Mass And Energy Exchange Net Mass Balance Dynamic Response Effect on Landscape Changes In Geometry Water Flow

3 PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM 1. Glacier-fed rivers provide much of the water supply in some parts of the world. Kaser et al., 2010 Antisana Mountain, Equador Dean Jacobsen

4 PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM 2a. Run-off characteristics (daily and seasonal) differ from other types of stream flow. mid- summer Vatnajökull Annes Hjemmeside Behrens, 1982 spring

5 PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM 2b. Contribution to regional runoff Klawatti Glacier Thunder Creek Basin spring

6 PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM 3. Run-off locally used for hydroelectric power generation. Switzerland Norway

7 PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM 4. Flood hazards in alpine areas from moraine-dammed and ice-dammed lakes. Hidden Lake, Kennicott Glacier Austin Post Thayer Glacier, North Sister, Oregon John Scurlock

8 PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM 4. Flood hazards in alpine areas from moraine-dammed and ice-dammed lakes.

9 What can we learn from observation?

10 In the accumulation zone

11 Ablation Zone

12 Ablation Zone

13 In front of the glacier Emmons Glacier John Scurlock Vatnajökull Annes Hjemmeside

14 Subglacial Conduit

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16 Hydrologic Cross Section of a Temperate Glacier

17 Firn water table in addition to percoulation

18 Firn water table

19 Englacial Passageways

20 Englacial Passageways

21 How do we learn about water flow through glaciers? Field studies of active glaciers Theoretical analysis Inferences from geomorphology

22 Field study of active glaciers Mass balance Stream monitoring (incl. hydrochemistry) Dye tracing Borehole-based studies Radio-echo sounding

23 Mass Balance Meltwater SURFACE INTERFLOW BASEFLOW

24 Stream Monitoring including hydrochemistry Englacial Water Subglacial Water

25 Dye tracing

26 Dye concentration Character of the dye return curve commonly changes as the melt season progresses. June 20 July 4 June 19 June 17 Hours since injection

27 Boreholes

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30 Fracture and Borehole

31 Depth Below Surface (m) Depth (m) Water Level Variations Site 3 2-Aug 4-Aug 6-Aug 8-Aug 10-Aug 12-Aug 14-Aug Water Level Variations Jul 24-Jul 28-Jul 1-Aug Date in

32 Reflector BH 3311 Borehole NE strike 38m ~4 cm Drainage Feature

33 Theoretical framework for glacier hydrology Field observations provide some constraints Thermodynamics, mechanics of materials provide additional constraints

34 Water is conveyed from glacier surface to bed and then discharged from the glacier. Cross section through glacier

35 Channel enclosed by ice (R channels) Channels in ice are self-formed and reflect a balance between melting of the walls (by energy dissipated in the flowing water) and creep of ice into the channel.

36 Channel enclosed by ice (R channels) Rate of change of channel cross-sectional area reflects difference between melting and creep closure. Water flow is impeded by friction. Energy dissipated by friction goes into melting. Water temperature stays at the pressure melting point.

37 Steady state R channel dpw = C (p i p w ) 24/11 dx Q 2/11 p w specified flow Q 1 Q 2 <Q 1 In steady state, flow should become concentrated into large channels, which are at lower pressure.

38 Arborescent R- channels

39 Insight from geomorphology Features exposed on recently deglaciated carbonate bedrock provide insights into geometry of subglacial drainage network. ICE FLOW

40 GLACIER DE FERPECLE, VALAIS, SWITZERLAND Robert Bingham

41 Blackfoot Glacier

42 Cavity network A cavity network has very different hydraulic properties than an arborescent channel network.

43 Cavity hydraulics Cavity formation is controlled by, sliding speed bed roughness water pressure

44 Cavity-network hydraulics dp w dx = C Q2 (p i p w ) h 13 3 u p w specified flow Q 2 <Q 1 Q 1 In steady state, flow should become concentrated into larger cavities, which are at higher pressure.

45 Arborescent nonarborescent R- channels Cavities

46 dpw = C (p i p w ) 24/11 dx Q 2/11

47 Role of till at the bed Suppose bed is primarily sediment (till).

48 Ice and sediment tend to flow in to fill channel. Water flow enlarges conduit by melting and also transports sediment. Till canal physics

49 Seasonal Drainage system evolution Basal drainage system tend to collapse during winter Early in melt season cavity dominate Rapid increase in water flux to bed destabilizes linked cavity network and promotes R channel formation

50 Summary of Glacier Hydrology

51 flotation Water and glacier sliding Dependence of speed on water pressure has changed over time at a single glacier. Unteraargletscher, Switzerland

52 Hydrology of ice sheets Most of the interior of large ice sheets frozen to the bed. At least locally temperate ice near margins. Basal water plays important role in rapid movement of ice streams. Glacial geology as a way to infer conditions beneath ice sheets?

53 Antarctica Fig. 4. (Top left) ICESat 91-day tracks across newly discovered Subglacial Lake Engelhardt on northwestern WIS. H A Fricker et al. Science 2007;315:

54 Joughin NASA

55 Zwally

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57 END Jason Gulley