GEOMORPHOLOGY EXAM #3
Formation of Glaciers
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Transformation of snow into glacial ice
Density;
SNOW = 0.07 – 0.18 g/cc
FIRN(Neve) = 0.4 – 0.8 g/cc (Pellets)
GLACIAL ICE = 0.8 – 0.9 g/cc
Firn / Ice Boundary = change to glacial ice (50 m – 160 meters deep)
Fabric
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‘Pressure Melting Point’ – melting point decreases with increased pressure.
Types;
THERMAL
‘Temperate’(Warm Based) – ice at or near pressure melting point through its thickness.
-At pressure melting point through entire thickness.
-Upper few meters frozen during winter months
-‘Wet Glaciers’ – melt water at the base and throughout the entire glacier.
‘Polar’(Cold Based) – ice is entirely below pressure melting temperature.
-Plastic flow slow, No basal sliding
-Only Ablation is calving, wind erosion, and sublimation
-Velocity slow (few meters a year)
-Meltwater and Basal sliding are absent (no bedrock erosion, no outwash plains)
‘Subpolar’ – frozen to their substrate, surface melting occurs in Summer.
-intermediate between temperate and polar glaciers
-have characteristics of both Polar & Temperate Glaciers
DYNAMIC – Active vs. Stagnant
‘Active’ – High Rates of Movement
‘Passive’ – Low Rates of Movement
‘Dead’ – No Movement, inactive, dormant
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Glacier movement rates greater near Upper Center of glacier
Thickness, Temperature, Slope, and Basal Water Pressure affect Velocity
Max Velocities happen at the Firn Line (equilibrium line)
Accumulation / Ablation Zones
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‘Plastic Flow’ – low levels of stress cause the ice to flow as plastic, ice spreading out near
margin.
-‘Infinite Yield Stress’ – will flow at only 1 bar of stress, once elastic is reached.
Types;
Interganular Shifting – rotation & sliding between x’ls
Intraganular Shifting – basal plane gliding (deck of cards, parallel/perpendicular)
Recrystallization – melting and refreezing down-ice
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‘Basal Sliding’ – greatest in Temperate Glaciers, thin glaciers with high slopes.
Relatively small % of total movement, Often a stick-slip jerky motion. Greatest % of
rocks at the bed, creates crescentric gouges, chatter marks, striations, ect.
MORPHOLOGICAL – often related to topographic influence.
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Alpine
‘small cirque glaciers’ – limited to area near firn line
more frequent on N & E facing slopes in the NH
‘valley glaciers’ – flow beyond their cirques
Piedmont
‘valley glaciers’ that extend into valley floor below
broad radiating lobes
Ice Sheet / Ice Cap
Large glaciers
not confined by topography
‘Ice Sheet’ – large
Greenland (1.7 million sq km.)
Antarctic (13 million sq km.)
‘Ice Cap’ – small
>50,000 sq km. (Baffin Island,CAN. & Iceland)
Dynamic Classification of Glaciers
‘Mass Balance’ – relation between accumulation/ablation
-Advancing
-Retreating
-Stationary
Budget of a Glacier
Zone of Accumulation – freezing, adding to a glacier
Zone of Ablation - melting, removing of a glacier
‘Firn’ – snow line, (equilibrium line) may not necessarily
be the same, but usually are.
Accumulation
All processes by which snow & ice are added to the glacier.
-Snow
-Ice/Snow Avalanches
-Drifting
Ablation
All processes snow & ice are lost
-Melting
-Evaporation
-Sublimation (evap., 1% loss)
-Calving (water depth & movement rate)
-Wind Erosion
-Heat (comes from solar, geothermal, air, rain)
Net Mass Balance
Difference in annual budgets of accumulation/ablation
Accumulation/Ablation equal, mass balance = 0
Accumulation > Ablation – balance is positive
Accumulation < Ablation – balance is negative
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Terminus position directly affected by balance
Accumulation = Forward, Ablation = Retreat
Climatic response time
Lags behind
Compressive/Expansive Flow
Internal Shearing
Occurs in upper 30 m or near terminus along
Planes of slippage.
Mechanisms for bringing basal debris to surface.
Compressive Flow – develops ‘Crevasses’
Glacier Surges – rapid advances
Dramatic thinning of ice
Rapid movement
Mechanisms of Glacier Surges;
Rigid bed Hypothesis – closure of subglacier drainage tunnels, increase H20 P
Deformable bed Hypothesis – bulge develops in lower reaches of glacier, boundary between
cold/warm based zones. H20 P builds, sediment is slurry, and thickening leads to increase of
basal shear stress.
Glacial Hydrology
Temperate Glaciers
May cause surges;
Frozen Toe
Causes water pressure to build
“Floats Ice” – reduces effective pressure
Surges often associated with ‘Jokulhlaups’ (Iceland term) – glacial outburst floods
‘Ogives’ – arrhythmic banding of differing tone and
color, has seasonal/annual ridges.
Ridge = 1 years ice flow
Differing Colors = Winter / Summer
Crevasses
Glacial Erosion
Abrasion
Plucking
division based on 2 observations;
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Interpretation of
‘Roches Moutinees’ One side is smooth/polished, the other is jagged/blocky.
Component of glacial debris (Rock floor & Rock fragments)
Abrasion
Bedrock is scoured by debris carried in basal layers of ice.
Evidence;
Striations
Rock Flour
Variables;
Requirements: Basal debris, Sliding basal ice, Transport of debris toward bedrock.
Factors: Ice thickness, Basal water pressure, Hardness, Particle characteristics, removal of
Rock Flour.
Regulation – incorporation of water refreezing under ice, pressure
melting causes an incorporation of debris.
(esp. at high pressure points)
‘Rat-tails’
‘Erratic’
‘Striations’
‘Cresentric Fracture’
‘Glacial Grove’
‘Cresentric Gouge’
Cirques – bowl shaped top, surrounded by headwalls.
Tarn – lake that occupies a Cirque.
Pater-Noster Lakes – Tarns connected by a stream.
(String of beads)
Horn – steep peak
Arête – steep walled ridge separating 2 glacial valleys,
sharp, Jagged.
Col – separation of 2 glaciers between 2 back to back
Cirques.
TYPES of Erosion
Abrasion
large blocks in basal ice
Rock Fracture
large blocks in basal ice
Joint Exploitation
hard jointed rock, suitable bedding
Entrainment (ice pressure)
large fragments
Entrainment (regulation)
small fragments
Meltwater Erosion
impermeable bedrock, soluble bedrock
Meltwater Evacuation
impermeable bedrock
Moraine – ridge of glacial sediment, layers or ridges of till.
Lateral Moraine – sides of glacier, alpine only, parallel to flow.
Medial Moraine –middle of glacier, alpine only, parallel to flow.
End Moraine – abalation = accumulation, a location
where the glacier was at equilibrium for a while,
composed of sediment/till. Perpendicular to floods. Terminal or
Recessional.
Ground Moraine – flat broad layer of sediment 1-10 meters high,
near head of glacier, composed of sediement/till. No orientation,
can happen in all glaciers except polar. Plastered under glacier.
Interlobate Moraine- confluence of 2 glacial lobes where the
Dumping of large boulders makes a valley, lakes, and steep topography.
Rogen Moraine- shearing at base of ice. Cavity filled with sediments where ice sheared upward
to clear an object. (Occurs in bunches)
Ice Shove Moraine (Push Moraine)- unconsolidated sediments (vertical), sand was frozen
Ice then advanced, bulldozing the sediment vertical. Perpendicular to flow.
‘Ice Shove Moraine’
‘Rogan Moraine’
Glacial Depositional Landforms
Kettle – depression in outwash plain
Kettle Lakes – depression filled with water
in the outwash plain, where a block of ice
stuck in the ground melts.
Kettle Chains – bumpy topography,
Glaciers melt, covers area in sediment,
But melt water collects in depressions.
Outwash Plain – gently sloping, braided streams,
sand & gravel, well sorted, good gravel pits. Composed
of stratified drift deposited by melt water leaving the glacier.
Consists of sand, gravel. Stratification, alternating of size,
Cross bedding can see flow directions.
Kame – accumulations of sand/gravel, conic
shape, where debris gathered after moulins dumped
it within the glacier. Ice Contact
Kame Delta- if stream came out of the glacier and
formed a delta.
Kame Terraces- deposits of meltwater streams flowing
between the ice and the adjacent valley side.
Esker – sub-glacial stream deposits within the glacier,
elevated because of its tunnel-like shape, good gravel pits.
Drumlin – teardrop shape, range in size 0-5 meters, mile or
so long, usually in a drumlin field, 5-10 km up ice from
End Moraine. Current Hypothesis = water at bed of the
glacier is responsible. Or an obstruction, collects material
behind it as the glacier passes. Streamlined sub-glacial landform.
Can form from pencil like to blunt. Contain till & outwash both.
Rock Drumlin- caused an obstruction to the ice flow.
Crag-and-Tail- A mass of rock lying in the path of a glacier
which protects the softer rock in the lee beyond it.
Flutes –low linear pencil like ridges.
Glacial Sediments (drift)
Unsorted & Unstratified
Till- laid directly by glacial ice, not reworked. Formed
underneath at margins. Can be rocky around Moraines.
(Till Lodgement)Basal Till – sediments at the bottom of glacier.
Basal or Lodgement
Ablation
Melt-out
Flow
Sorted & Stratified (layered)
Glaciofluvial (Fluvioglacial)
Till
Diamicton – any unsorted or unstratified mix of sediment.
Basal Ablation, Flow
Glaciomarine, Glaciolacustrine
Poorly sorted, not stratified, compacted, faceted, polished, stratified stones, fabric,
Erratic lithologies, deformed sediments
Glaciomarie- poorly sorted, lacks stratification, marine shells, polished, faceted, striated clasts,
mollusks berried in growth position, preservation of delicate ornamentation.
Plunge Pool – a glacial front in a spot where heavy
flow dumps(waterfall) onto the outwash plane.
Isostatic Rebound – weight of the glacier pushed land down, but now is rebounding back to up.
WhaleBacks – typical in hummocky terrain, small isolated hill, looks similar to a whales back.
Hummocky Glacial Terrain – rolling ridges, irregular lakes, depressions, kettles
Ice-Walled Lake Plain – a glacial lake
that had ice form its shoreline, when
the glacier melted a flat plain resided.
Varves(in glaciers) Rhythmites
Alternating layers
Summer = coarser, lighter colors (because flow increases and more sediments are moved)
Winter = finer silts, darker
Thickness is reliant on the stream.
‘Varve’
‘Continental Glacier’ – large
‘Alpine Glacier’ – small
‘Rhythmites’