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