Glacier hydrology - Portland State University · Glacier Hydrology Why should you care? Water Flow...
Transcript of Glacier hydrology - Portland State University · Glacier Hydrology Why should you care? Water Flow...
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Glacier Hydrology Why should you care?
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Water Flow
Climate
Local Meteorology
Surface Mass And
Energy Exchange
Net Mass Balance
Dynamic Response
Changes In
Geometry Effect on Landscape
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PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM
1. Glacier-fed rivers provide much of the water supply in some parts of the world.
Antisana Mountain, Equador Dean Jacobsen
Kaser et al., 2010
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PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM
2a. Run-off characteristics (daily and seasonal) differ from other types of stream flow.
spring
mid- summer
Annes Hjemmeside Behrens, 1982
Vatnajökull
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PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM
spring
2b. Contribution to regional runoff
Klawatti Glacier Thunder Creek Basin
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PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM
3. Run-off locally used for hydroelectric power generation.
• Switzerland • Norway
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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
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PRACTICAL MATTERS: GLACIERS IN THE HYDROLOGICAL SYSTEM
4. Flood hazards in alpine areas from moraine-dammed and ice-dammed lakes.
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What can we learn from observation?
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In the accumulation zone
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Ablation Zone
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Ablation Zone
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Annes Hjemmeside Vatnajökull
In front of the glacier
Emmons Glacier John Scurlock
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Subglacial Conduit
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Hydrologic Cross Section of a Temperate Glacier
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Firn water table……in addition to percoulation
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Firn water table
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Englacial Passageways
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Englacial Passageways
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How do we learn about water
flow through glaciers?
• Field studies of active glaciers
• Theoretical analysis
• Inferences from geomorphology
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Field study of active glaciers
• Mass balance
• Stream monitoring (incl. hydrochemistry)
• Dye tracing
• Borehole-based studies
• Radio-echo sounding
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Mass Balance
SURFACE
INTERFLOW
BASEFLOW
Meltwater
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Stream Monitoring – including hydrochemistry
Subglacial Water
Englacial
Water
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Dye tracing
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Dye
conce
ntr
atio
n
Hours since injection
June 17
June 19
June 20
July 4
Character of the dye return curve commonly changes as the melt season progresses.
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Boreholes
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Fracture and Borehole
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Site 3
5
10
15
20
25
30
35
2-Aug 4-Aug 6-Aug 8-Aug 10-Aug 12-Aug 14-Aug
De
pth
(m
)
Water Level Variations
311 39
0
5
10
15
20
25
20-Jul 24-Jul 28-Jul 1-Aug
Date in 2002
De
pth
Be
low
Su
rfa
ce
(m
)
0
5
10
15
20
25
311 32
Water Level Variations
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3 Reflector
38m
Drainage
Feature
BH 311
Borehole
NE strike
~4 cm
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Theoretical framework for glacier
hydrology
• Field observations provide some constraints
• Thermodynamics, mechanics of materials
provide additional constraints
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Cross section through glacier
Water is
conveyed
from glacier
surface to bed
and then
discharged
from the
glacier.
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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.
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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.
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Steady state R channel
Q2<Q1
pw
specified
Q1
flow
In steady state, flow should become concentrated
into large channels, which are at lower pressure.
𝑑𝑝
𝑑𝑥 =
𝐶 (𝑝𝑖 – 𝑝𝑤 )24/11
𝑄2/11 w
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Arborescent R- channels
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Insight from geomorphology
Features exposed
on recently
deglaciated
carbonate bedrock
provide insights
into geometry
of subglacial
drainage network.
ICE FLOW
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GLACIER DE FERPECLE, VALAIS, SWITZERLAND Robert Bingham
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Blackfoot Glacier
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Cavity network
A cavity network has very
different hydraulic
properties than an
arborescent channel
network.
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Cavity hydraulics
Cavity formation is
controlled by,
• sliding speed
• bed roughness
• water pressure
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Cavity-network hydraulics
pw
specified Q1
flow
Q2<Q1
𝑑𝑝𝑤𝑑𝑥
= 𝐶 𝑄2(𝑝𝑖 − 𝑝𝑤)
ℎ133
𝑢
In steady state, flow should become concentrated
into larger cavities, which are at higher pressure.
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Arborescent nonarborescent R- channels Cavities
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𝑑𝑝
𝑑𝑥 =
𝐶 (𝑝𝑖 – 𝑝𝑤 )24/11
𝑄2/11 w
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Role of till at the bed Suppose bed is primarily sediment (till)….
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Till canal—physics
Ice and sediment
tend to flow in to
fill channel. Water
flow enlarges
conduit by melting
and also transports
sediment.
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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
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Summary of Glacier Hydrology
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Water and glacier sliding
Dependence of
speed on water
pressure has
changed
over time at a single
glacier.
Unteraargletscher,
Switzerland
flota
tion
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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?
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Fig. 4. (Top left) ICESat 91-day tracks across newly discovered Subglacial Lake Engelhardt on
northwestern WIS.
H A Fricker et al. Science 2007;315:1544-1548
Antarctica
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Joughin
NASA
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Zwally
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END
Jason Gulley