Snow / Ice / Climate I Energy and Mass “The Essence of Glaciology” “The Essence of Glaciology” Processes of: Processes of: accumulation – precipitation accumulation – precipitation ablation – melt, sublimation, calving ablation – melt, sublimation, calving wind & avalanche can affect either wind & avalanche can affect either Transformation of snow  firn  ice Transformation of snow  firn  ice takes time – depends on mass, temperature, etc takes time – depends on mass, temperature, etc Balance of acc & abl  energy budget Balance of acc & abl  energy budget

Energy and Mass The annual energy budget of a glacier is the sum of inputs minus the sum of outputs ± changes in storage. The annual energy budget of a glacier is the sum of inputs minus the sum of outputs ± changes in storage. The annual mass budget of a glacier is the specific (at-a-point) budget times the area to which it applies, summed across the entire glacier: The annual mass budget of a glacier is the specific (at-a-point) budget times the area to which it applies, summed across the entire glacier: B n = Σ (1-i) (b ni x A i ) B n = Σ (1-i) (b ni x A i )

Energy Budget INPUTSOUTPUTS INPUTSOUTPUTS Solar (short-wave) radiationReflection [albedo] Solar (short-wave) radiationReflection [albedo] Long-wave radiationLong-wave Long-wave radiationLong-wave Conduction (air)Conduction Conduction (air)Conduction Conduction (ground) Conduction (ground) Convection (air) [sensible]Convection Convection (air) [sensible]Convection Latent heatLatent heat Latent heatLatent heat Condensation, freezing Evaporation, melt Condensation, freezing Evaporation, melt ?? energy from sliding/friction, water flow ? ?? energy from sliding/friction, water flow ?

Energy Balance? Varies with position on a glacier, time of day, season, cloud cover, wind … Varies with position on a glacier, time of day, season, cloud cover, wind … Convection often estimated by difference (assuming balance) Convection often estimated by difference (assuming balance) “Balance” implies no change in storage (temperature) “Balance” implies no change in storage (temperature) Studies are rare because of difficulty. Studies are rare because of difficulty.

Examples of Energy Budgets

Specific Mass Budget – Stratigraphic Most commonly, End Of Summer to EOS Most commonly, End Of Summer to EOS Uses old snow / firn / ice as a marker Uses old snow / firn / ice as a marker

Specific Mass Budget Protocols Stakes = aluminum conduit melted into ice Stakes = aluminum conduit melted into ice Winter balance (b w ) Winter balance (b w ) b w = depth of snow x density (= “water equivalent”) b w = depth of snow x density (= “water equivalent”) Summer balance (b S ) Summer balance (b S ) b s = b n – b w (accumulation area) b s = b n – b w (accumulation area) b s = b w + lost ice times (ablation area) b s = b w + lost ice times (ablation area) Firn line, b n = 0 Firn line, b n = 0 Equilibrium line altitude (ELA), b n = 0 Equilibrium line altitude (ELA), b n = 0

Specific Mass Budget Trends Accumulation often increases slightly with increasing altitude above the ELA. Accumulation often increases slightly with increasing altitude above the ELA, b n = ELA, b n = 0 Ablation increases rapidly with decreasing altitude below the ELA. Ablation increases rapidly with decreasing altitude below the ELA.

Specific Mass Budget with Climate “Accumulation gradient” = Δmass acc /Δelevation = mm H2O /m elevation “Accumulation gradient” = Δmass acc /Δelevation = mm H2O /m elevation “Ablation gradient” = Δmass abl /Δelevation = mm H2O /m elevation “Ablation gradient” = Δmass abl /Δelevation = mm H2O /m elevation “Activity gradient” = ELA “Activity gradient” = ELA Maritime = high activity gradient Maritime = high activity gradient Continental = low A.G. Continental = low A.G.

Specific Mass Budget with Climate “Accumulation gradient” = Δmass acc /Δelevation = mm H2O /m elevation “Accumulation gradient” = Δmass acc /Δelevation = mm H2O /m elevation “Ablation gradient” = Δmass abl /Δelevation = mm H2O /m elevation “Ablation gradient” = Δmass abl /Δelevation = mm H2O /m elevation “Activity gradient” = ELA “Activity gradient” = ELA Maritime = high activity gradient Maritime = high activity gradient Continental = low A.G. Continental = low A.G.

Why is the ablation gradient >> the accumulation gradient? Accumulation = f (precip) Accumulation = f (precip) Ablation = f (melt) Ablation = f (melt) Melt = f (T, albedo) Melt = f (T, albedo) snow ~ 0.9 snow ~ 0.9 ice ~0.5 ice ~0.5 debris ~ 0.2, BUT can also insulate debris ~ 0.2, BUT can also insulate other reasons? other reasons?

Specific Mass Budget with Time Remarkably consistent! Remarkably consistent! Shape = f (climate) Shape = f (climate) Position = f (weather) Position = f (weather)

Snow / Ice / Climate II Snowlines – Space and Time Snowlines and their many definitions Snowlines and their many definitions Estimating b n = 0 Estimating b n = 0 Contemporary controls on snowlines Contemporary controls on snowlines local climate / weather and topography local climate / weather and topography Spatial variability Spatial variability Temporal variability Temporal variability Pleistocene snowlines and climates Pleistocene snowlines and climates

Snowlines I – Cirque Floors Permanent snowfields? No – glaciers! Permanent snowfields? No – glaciers! Cirque floor elevations Cirque floor elevations Maximum erosion at minimum size Maximum erosion at minimum size Problems = size, timing Problems = size, timing

Snowlines II – Lateral Moraines Highest laterals = initiation of deposition [discuss more with “glacier flow” ?] Highest laterals = initiation of deposition [discuss more with “glacier flow” ?] Problem = postglacial slope erosion/removal Problem = postglacial slope erosion/removal

Snowlines III – Glaciation Threshold True “snowline” True “snowline” Problems = many Problems = many Area? Area? Topography? Topography? Summits > glacier elevations Summits > glacier elevations

Snowlines IV – THAR Toe-headwall altitude ratio Toe-headwall altitude ratio Requires reconstruction Requires reconstruction Assumes known “correct” ratio – 40%? Assumes known “correct” ratio – 40%?

Snowlines V – AAR Accumulation area ratio Accumulation area ratio Requires complete reconstruction Requires complete reconstruction Assumes correct ratio.55–.60–.65 ? Assumes correct ratio.55–.60–.65 ? [topo map method] [topo map method]

Snowline Comparisons Meierding (1982) Meierding (1982) CO Front Range CO Front Range tried many ratios tried many ratios Locke (1990) Locke (1990) Montana Montana small glaciers small glaciers s.d. ~ 350 m s.d. ~ 350 m CF (n=12) 3161 m LM (45) 3188 GT (13) 3388 THAR (24) 3161 (40%) AAR (24) 3163 (65%) CF (n=400) 2347 m LM (321) 2121 THAR (330) 2355 (40%) AAR (264) 2353 (65%)

ELA = representative? Many studies say so! Many studies say so! e.g., Sutherland (1984) e.g., Sutherland (1984) ELA balance represents average winter balance for entire glacier ELA balance represents average winter balance for entire glacier Measure once – use a lot! Measure once – use a lot!

Glacial Climates Glaciers exist only in a narrow range of climates Glaciers exist only in a narrow range of climates = f(winter ppt and summer T) = f(winter ppt and summer T) = f(P, T, and continentality = f(P, T, and continentality

Glacial Climates

Controls on Snowlines I – Latitude Latitude ≈ temperature (treeline) Latitude ≈ temperature (treeline) highest near equator highest near equator Latitude ≠ precipitation (snowlines) Latitude ≠ precipitation (snowlines) saddle near equator saddle near equator Weak gradients (<1 m/km) Weak gradients (<1 m/km)

Controls II – Continentality Lowest near moisture source Lowest near moisture source Higher inland Higher inland Strong gradients Strong gradients up to 10 m/km up to 10 m/km

No Hem Glaciers Latitude? Latitude? Continentality Continentality Ocean currents Ocean currents Local precipitation Local precipitation

Temporal Resolution Glaciers respond at annual to decadal scales Glaciers respond at annual to decadal scales

Temporal Inconsistency Not all glaciers respond similarly Not all glaciers respond similarly Not even glaciers in the same region! Not even glaciers in the same region!

Temporal Inconsistency Not all glaciers respond similarly Not all glaciers respond similarly Not even glaciers in the same region! Not even glaciers in the same region!

Pleistocene Snowlines I Sierra Nevada Sierra Nevada Note effects of subtropical high & rain shadow Note effects of subtropical high & rain shadow Wahrhaftig and Birman, 1965

Pleistocene Snowlines II US West (Porter et al. 1983) US West (Porter et al. 1983) Effects of: Effects of: SubT High SubT High Westerlies Westerlies Storm tracks Storm tracks Orography Orography

Pleistocene Snowlines II

Montana Climate & Glaciers Glaciers Glaciers Inferred air mass movement Inferred air mass movement Residuals Residuals Inferred causes Inferred causes

MT/ID Paleoclimate Complex pattern! Complex pattern! More detailed than modern weather stations and SNOTEL sites! More detailed than modern weather stations and SNOTEL sites!

Spatial Resolution Humlum (1985) Humlum (1985) West Greenland West Greenland Local data are consistent Local data are consistent Needs no smoothing Needs no smoothing High resolution! High resolution!