snow / ice / climate i energy and mass “the essence of glaciology” “the essence of...

Snow / Ice / Climate ISnow / Ice / Climate IEnergy and MassEnergy and Mass

““The Essence of Glaciology”The Essence of Glaciology” Processes of:Processes of:

accumulation – precipitationaccumulation – precipitation ablation – melt, sublimation, calvingablation – melt, sublimation, calving

wind & avalanche can affect eitherwind & avalanche can affect either

Transformation of snow Transformation of snow firn firn ice ice takes time – depends on mass, temperature, takes time – depends on mass, temperature,

etcetc Balance of acc & abl Balance of acc & abl energy budget energy budget

Energy and MassEnergy and Mass The annual The annual energy budgetenergy budget of a of a

glacier is the sum of inputs minus the glacier is the sum of inputs minus the sum of outputs ± changes in storage.sum of outputs ± changes in storage.

The annual The annual mass budgetmass budget of a glacier of a glacier is the is the specificspecific (at-a-point) budget (at-a-point) budget times the area to which it applies, times the area to which it applies, summed across the entire glacier:summed across the entire glacier:

BBnn = = ΣΣ(1-i) (1-i) (b(bnini x A x Aii))

Energy BudgetEnergy Budget

INPUTSINPUTS OUTPUTSOUTPUTS Solar (short-wave) radiationSolar (short-wave) radiation Reflection [albedo]Reflection [albedo] Long-wave radiationLong-wave radiation Long-waveLong-wave Conduction (air)Conduction (air) ConductionConduction Conduction (ground)Conduction (ground) Convection (air) [sensible]Convection (air) [sensible] ConvectionConvection Latent heatLatent heat Latent heatLatent heat

Condensation, freezingCondensation, freezing Evaporation, melt Evaporation, melt ?? energy from sliding/friction, water flow ??? energy from sliding/friction, water flow ?

Energy Balance?Energy Balance?

Varies with position on a glacier, time Varies with position on a glacier, time of day, season, cloud cover, wind …of day, season, cloud cover, wind …

Convection often estimated by Convection often estimated by difference (assuming balance)difference (assuming balance)

““Balance” implies no change in Balance” implies no change in storage (temperature)storage (temperature)

Studies are rare because of difficulty.Studies are rare because of difficulty.

Examples of Energy Examples of Energy BudgetsBudgets

SpecificSpecific Mass Budget – Mass Budget – StratigraphicStratigraphic

Most commonly, End Of Summer to EOSMost commonly, End Of Summer to EOS Uses old snow / firn / ice as a markerUses old snow / firn / ice as a marker

Specific Mass Budget Specific Mass Budget ProtocolsProtocols

Stakes = aluminum conduit melted into iceStakes = aluminum conduit melted into ice Winter balance (bWinter balance (bww))

bbww = depth of snow x density (= “water = depth of snow x density (= “water equivalent”)equivalent”)

Summer balance (bSummer balance (bSS)) bbss = b = bn n – b– bww (accumulation area) (accumulation area) bbss = b = bww + lost ice times 0.917 (ablation area) + lost ice times 0.917 (ablation area)

Firn line, bFirn line, bnn = 0 = 0 Equilibrium line altitude (ELA), bEquilibrium line altitude (ELA), bnn = 0 = 0

Specific Mass Budget Specific Mass Budget TrendsTrends

Accumulation often Accumulation often increases slightly increases slightly with increasing with increasing altitude above the altitude above the ELA.ELA.

@ ELA, b@ ELA, bnn = 0 = 0 Ablation increases Ablation increases

rapidly with rapidly with decreasing altitude decreasing altitude below the ELA.below the ELA. (+)(-)

Mass Exchange (m H2O)

Summer budget (bs)

Netbudget

(bn)

Winterbudget

(bw)

Specific Mass Budget with Specific Mass Budget with ClimateClimate

““Accumulation gradient” Accumulation gradient” = = ΔΔmassmassaccacc//ΔΔelevationelevation= mm= mmH2OH2O/m/melevationelevation

““Ablation gradient”Ablation gradient”= = ΔΔmassmassabl abl //ΔΔelevationelevation= mm= mmH2OH2O/m/melevationelevation

““Activity gradient”Activity gradient”= gradient @ ELA= gradient @ ELA

Maritime = high Maritime = high activity gradientactivity gradient

Continental = low A.G.Continental = low A.G.

Specific Mass Budget with Specific Mass Budget with ClimateClimate

““Accumulation gradient” Accumulation gradient” = = ΔΔmassmassaccacc//ΔΔelevationelevation= mm= mmH2OH2O/m/melevationelevation

““Ablation gradient”Ablation gradient”= = ΔΔmassmassabl abl //ΔΔelevationelevation= mm= mmH2OH2O/m/melevationelevation

““Activity gradient”Activity gradient”= gradient @ ELA= gradient @ ELA

Maritime = high Maritime = high activity gradientactivity gradient

Continental = low A.G.Continental = low A.G.

Why is the ablation gradient >>Why is the ablation gradient >>the accumulation gradient?the accumulation gradient?

Accumulation = Accumulation = f (precip)f (precip)

Ablation = f (melt)Ablation = f (melt) Melt = f (T, albedo)Melt = f (T, albedo)

snow ~ 0.9snow ~ 0.9 ice ~0.5ice ~0.5 debris ~ 0.2, BUT debris ~ 0.2, BUT

can also insulatecan also insulate

other reasons?other reasons?

Specific Mass Budget with Specific Mass Budget with TimeTime

Remarkably Remarkably consistent!consistent!

Shape = Shape = f f

(climate)(climate) Position = Position = f f

(weather)(weather)

Snow / Ice / Climate IISnow / Ice / Climate IISnowlines – Space and TimeSnowlines – Space and Time

Snowlines and their many definitionsSnowlines and their many definitions Estimating bEstimating bnn = 0 = 0

Contemporary controls on snowlinesContemporary controls on snowlines local climate / weather and topographylocal climate / weather and topography

Spatial variabilitySpatial variability Temporal variabilityTemporal variability Pleistocene snowlines and climatesPleistocene snowlines and climates

Snowlines I – Cirque FloorsSnowlines I – Cirque Floors

Permanent snowfields? No – glaciers!Permanent snowfields? No – glaciers! Cirque floor elevationsCirque floor elevations

Maximum erosion at minimum sizeMaximum erosion at minimum size Problems = size, timingProblems = size, timing

Snowlines II – Lateral Snowlines II – Lateral MorainesMoraines

Highest laterals = initiation of depositionHighest laterals = initiation of deposition[discuss more with “glacier flow” ?][discuss more with “glacier flow” ?] Problem = postglacial slope erosion/removalProblem = postglacial slope erosion/removal

Snowlines III –Snowlines III –Glaciation ThresholdGlaciation Threshold

True True “snowline”“snowline”

Problems = Problems = manymany Area?Area? Topography?Topography? Summits > Summits >

glacier glacier elevationselevations

Snowlines IV – THARSnowlines IV – THAR

Toe-headwall altitude ratioToe-headwall altitude ratio Requires reconstructionRequires reconstruction Assumes known “correct” ratio – 40%?Assumes known “correct” ratio – 40%?

Snowlines V – AARSnowlines V – AAR Accumulation Accumulation

area ratioarea ratio Requires Requires

complete complete reconstructionreconstruction

Assumes Assumes correct correct ratio .55–.60–.6ratio .55–.60–.65 ?5 ?

[topo map method][topo map method]

Snowline ComparisonsSnowline Comparisons

Meierding Meierding (1982)(1982) CO Front RangeCO Front Range tried many tried many

ratiosratios

Locke (1990)Locke (1990) MontanaMontana small glacierssmall glaciers s.d. ~ 350 ms.d. ~ 350 m

CF (n=12)CF (n=12) 3161 m3161 m

LM (45)LM (45) 31883188

GT (13)GT (13) 33883388

THAR (24)THAR (24) 3161 3161 (40%)(40%)

AAR (24)AAR (24) 3163 3163 (65%)(65%)CF CF

(n=400)(n=400)2347 m2347 m

LM (321)LM (321) 21212121

THAR THAR (330)(330)

2355 2355 (40%)(40%)

AAR (264)AAR (264) 2353 2353 (65%)(65%)

ELA = ELA = representative?representative?

Many studies say Many studies say so!so! e.g., Sutherland e.g., Sutherland

(1984)(1984) ELA balance ELA balance

represents represents averageaverage winter balance for winter balance for entire glacierentire glacier

Measure once – use a Measure once – use a lot!lot!

Glacial Glacial ClimatesClimates

Glaciers exist Glaciers exist only in a only in a narrow range narrow range of climatesof climates = f(winter = f(winter

ppt and ppt and summer T)summer T)

= f(P, T, and = f(P, T, and continentalitcontinentalityy

Glacial Glacial ClimatesClimates

Controls on Snowlines I – Controls on Snowlines I – LatitudeLatitude

Latitude Latitude ≈ temperature (treeline)≈ temperature (treeline) highest near equatorhighest near equator

Latitude ≠ precipitation (snowlines)Latitude ≠ precipitation (snowlines) saddle near equatorsaddle near equator

Weak gradients (<1 m/km)Weak gradients (<1 m/km)

Controls II – Controls II – ContinentaliContinentali

tyty Lowest near Lowest near

moisture moisture sourcesource

Higher inlandHigher inland Strong Strong

gradientsgradients up to 10 up to 10

m/kmm/km

No Hem No Hem GlaciersGlaciers

Latitude?Latitude? ContinentaliContinentali

tyty Ocean Ocean

currentscurrents Local Local

precipitatioprecipitationn

Temporal ResolutionTemporal Resolution

Glaciers respond at annual to decadal Glaciers respond at annual to decadal scalesscales

Temporal InconsistencyTemporal Inconsistency

Not all glaciers respond similarlyNot all glaciers respond similarly Not even glaciers in the same region!Not even glaciers in the same region!

Temporal InconsistencyTemporal Inconsistency

Not all glaciers respond similarlyNot all glaciers respond similarly Not even glaciers in the same region!Not even glaciers in the same region!

PleistocenePleistoceneSnowlinesSnowlines

II

SierraSierraNevadaNevada Note effects ofNote effects of

subtropical high &subtropical high &rain shadowrain shadow

Wahrhaftig and Birman, 1965

Pleistocene Pleistocene Snowlines Snowlines

IIII US WestUS West

(Porter et (Porter et al. 1983)al. 1983)

Effects of:Effects of: SubT HighSubT High WesterliesWesterlies Storm Storm

trackstracks OrographyOrography

Pleistocene Pleistocene Snowlines Snowlines

IIII

Montana Montana Climate & Climate & GlaciersGlaciers

GlaciersGlaciers Inferred air Inferred air

mass mass movementmovement

ResidualsResiduals Inferred Inferred

causescauses

MT/ID MT/ID PaleoclimatPaleoclimat

ee Complex Complex

pattern!pattern! More More

detailed detailed than modern than modern weather weather stations stations andand SNOTEL SNOTEL sites!sites!

Spatial Spatial ResolutionResolution

Humlum (1985)Humlum (1985) West GreenlandWest Greenland Local data are Local data are

consistentconsistent Needs no Needs no

smoothingsmoothing High resolution!High resolution!