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Glaciers and Glaciers and MeltwaterMeltwater
chapter 3chapter 3
Glacier hydrologyGlacier hydrologyWhy should you care?Why should you care?
Based on a lecture by Dr. J.S. Walder
Practical matters:Practical matters:glaciers in the hydrological glaciers in the hydrological
systemsystem Glacier-fed rivers provide much of the Glacier-fed rivers provide much of the
water supply in some parts of the world.water supply in some parts of the world.
Run-off characteristics (daily and seasonal) Run-off characteristics (daily and seasonal) differ from other types of stream flow.differ from other types of stream flow.
Run-off locally used for hydroelectric Run-off locally used for hydroelectric power generation.power generation.
Flood hazards in alpine areas from Flood hazards in alpine areas from moraine-dammed and ice-dammed lakes.moraine-dammed and ice-dammed lakes.
Glaciated vs. Unglaciated Glaciated vs. Unglaciated BasinsBasins
Minor (?) differences in Minor (?) differences in peakpeak and and totaltotal runoff runoff in snow-dominated basins (not rain-dominated)in snow-dominated basins (not rain-dominated)
Major difference is in Major difference is in timingtiming of runoff of runoff
Characteristics of Glacial QCharacteristics of Glacial Q During ablation season – strong daily During ablation season – strong daily
peakspeaks driven by energy inputsdriven by energy inputs f (cloudiness)f (cloudiness)
Characteristics of Glacial QCharacteristics of Glacial Q Ablation season – strong daily peaksAblation season – strong daily peaks
driven by energy inputsdriven by energy inputs f (cloudiness)f (cloudiness)
Anomalies – driven by internal/external Anomalies – driven by internal/external drainagedrainage (re)organization of flow paths?(re)organization of flow paths? kinematic waves?kinematic waves?
Glaciers and water Sources of water
surface subsurface
Water flow in glaciers open-channel, porous-media (Darcian)
or conduit flow? hydraulic potential storage: lakes and ponds
Supraglacial, englacial, subglacial drainage
Glacial-fluvial features outburst floods proglacial systems
Glaciers and waterGlaciers and water Explanation / discussion of hydraulic
potential in glaciers see text p 99 – 101
Glaciers and water Sources of water
surface subsurface
Water flow in glaciers open-channel, porous-media (Darcian)
or conduit flow? hydraulic potential storage: lakes and ponds (classification)
Supraglacial, englacial, subglacial drainage
Glacial-fluvial features outburst floods proglacial systems
Glacier dammed lakeGlacier dammed lake
Lake basinafter outburst
ice flow
Subglacialoutflow
This lake fills and drains everyyear.
Glaciers and water Sources of water
surface subsurface
Water flow in glaciers open-channel, porous-media (Darcian)
or conduit flow? hydraulic potential storage: lakes and ponds
Supraglacial, englacial, subglacial drainage
Glacial-fluvial features outburst floods proglacial systems
Supraglacial DrainageSupraglacial Drainage Melt occur because Melt occur because
of albedo, air of albedo, air temperaturetemperature
Snowpack becomes Snowpack becomes saturated, refreezes saturated, refreezes oror
Water runs offWater runs off Channel morphologyChannel morphology Flow to margin or Flow to margin or
snoutsnout
Supraglacial DrainageSupraglacial Drainage Melt occurs because Melt occurs because
of albedo, air of albedo, air temperaturetemperature
Snowpack becomes Snowpack becomes saturated, refreezes saturated, refreezes oror
Water runs offWater runs off Channel morphologyChannel morphology Flow to margin or Flow to margin or
snoutsnout Moulins to interior/bedMoulins to interior/bed
Ablation Zone
Englacial DrainageEnglacial Drainage
Positive feedbacks enlarge seeps to streamsPositive feedbacks enlarge seeps to streams Negative feedbacks close themNegative feedbacks close them
• See also http://www.glaciers-online.net/morteratsch/ice_cave_2009/index-en.html
The Subglacial SystemThe Subglacial System
f f (distance) (distance) down-icedown-ice
Water Water increases increases to the to the terminusterminus
Debris Debris decreases decreases below the below the terminusterminus
Subglacial ChannelsSubglacial Channels Eroded into bedrock (e.g., Eroded into bedrock (e.g.,
Antarctica)Antarctica) N (Nye) channelsN (Nye) channels PressurePressure ToolsTools
Subglacial DrainageSubglacial DrainageChannelized (fast) vs distributed Channelized (fast) vs distributed
(slow) flow (slow) flow Arborescent vs nonarborescent pathsArborescent vs nonarborescent paths
Cavity Cavity networknetwork
A cavity network has very different hydraulic properties than anarborescent channel network.
N- or R- channels ?
Insight from Insight from geomorphologygeomorphology
Features exposedon recentlydeglaciatedcarbonate bedrockprovide insightsinto the geometryof a subglacialdrainage network.
ice flow
Annes Hjemmeside
Vatnajökull
Dye tracing
Dye is poured into moulin or borehole.
Average properties of the drainage system can be inferred from dye return curves.
Boreholes
Dye
con
cent
rati
on
Hours since injection
June 17
June 19
June 20
July 4
Character of the dyereturn curve commonly changes as the melt seasonprogresses.
Subglacial Conduit
Subglacial ChannelsSubglacial Channels
EskersEskers
Copyright © Daryl Dagesse 2002
Eskers IIEskers II Impermeable Impermeable
bedbed Lane’s Lane’s
Balance?Balance? Gravity + Gravity +
hydrostatic hydrostatic pressurepressure
Typically flow Typically flow down-icedown-ice
Eskers IIEskers II Impermeable Impermeable
bedbed Lane’s Lane’s
Balance?Balance? Gravity + Gravity +
hydrostatic hydrostatic pressurepressure
Typically flow Typically flow down-icedown-ice
Glaciers and water Sources of water
surface subsurface
Water flow in glaciers open-channel, porous-media (Darcian)
or conduit flow? hydraulic potential storage: lakes and ponds
Supraglacial, englacial, subglacial drainage
Glacial-fluvial features outburst floods proglacial systems
Vatnajökull October 1, 1996
Magnús Tumi Guðmundsson
Science Institute, University of Iceland
Vatnajökull October 3, 1996
Magnús Tumi Guðmundsson
Science Institute, University of Iceland
Jökulhlaup, 5 November 1996
Magnús Tumi GuðmundssonFinnur Pálsson
Science Institute, University of Iceland
380 m long bridge across Gýgja has disappeared
Magnús Tumi GuðmundssonFinnur Pálsson
Science Institute, University of Iceland
Lake MissoulaLake Missoula The largest The largest
of many of many ice-ice-dammed dammed lakes in lakes in MontanaMontana
Lake MissoulaLake Missoula The largest The largest
of many of many ice-ice-dammed dammed lakes in lakes in MontanaMontana
Ice dam Ice dam dynamicsdynamics
Lake MissoulaLake Missoula The largest The largest
of many ice-of many ice-dammed dammed lakes in lakes in MontanaMontana
Ice dam Ice dam dynamicsdynamics
ReconstructReconstructed ed dischargesdischarges
Glaciers and Glaciers and Meltwater IIMeltwater II
Outwash Streams and Outwash Streams and SedimentSediment
Sources of sediment and debrisSources of sediment and debris
Kames: Kames: Terraces/Moulins/DeltasTerraces/Moulins/Deltas
““Ice-contact Ice-contact glacio-fluvial”glacio-fluvial”
Normal Normal faultingfaulting
Proximal OutwashProximal Outwash
Proximal OutwashProximal Outwash
Outwash SedimentologyOutwash Sedimentology
FaciesFacies DistributiDistributi
onon
Outwash SedimentologyOutwash Sedimentology
FaciesFacies DistributiDistributi
onon DownstreDownstre
am am evolutionevolution
Outwash Outwash SedimentologSedimentolog
yy FaciesFacies DistributionDistribution DownstreaDownstrea
m evolutionm evolution
Copyright © Jeff Munro 2002
Pitted OutwashPitted Outwash
Outwash TerracesOutwash Terraces MorphologyMorphology
TheoreticalTheoretical ActualActual
Rock Creek, MontanaRock Creek, Montana
Ritter Ritter (1972)(1972) EvolutionEvolution Q/LoadQ/Load
Reheis Reheis (1987)(1987) SequenceSequence
Rock Creek, MontanaRock Creek, Montana
Ritter Ritter (1972)(1972) EvolutionEvolution Q/LoadQ/Load
Reheis Reheis (1987)(1987) SequenceSequence
from Reheis (1987)
Downstream SequencesDownstream Sequences How far downstream can an outwash How far downstream can an outwash
terrace persist?terrace persist?
Shoshone River terracesShoshone River terraces All surfaces fit quadratic modelsAll surfaces fit quadratic models Younger (last glacial) converges across Younger (last glacial) converges across
85 km85 km Older (Illinoisan?) is Older (Illinoisan?) is
asymptotic/”parallel”.asymptotic/”parallel”.
Shoshone Shoshone summarysummary
Last glacial terracesLast glacial terraces are finite/convergeare finite/converge require >14,000 yrrequire >14,000 yr Are still progradingAre still prograding
Older terracesOlder terraces ““parallel” the riverparallel” the river denudation anddenudation and
isostasy?isostasy? What about more complex river What about more complex river
systems?systems?
Modernanabranching
Wisconsinan
Illinoisan
Yellowstone River terracesYellowstone River terraces Last glacial = finite, older = river-parallel?Last glacial = finite, older = river-parallel? Show evidence of local sediment supplyShow evidence of local sediment supply Anomalous reaches require other data Anomalous reaches require other data
(provenance, age) to decipher(provenance, age) to decipher
Shreve’s Shreve’s ModelModel
LandscapeLandscape ModelModel
1 bar1 bar 0.5 bar0.5 bar 0.25 bar0.25 bar