Glacial landforms (geomorphology)

DEPARTMENT OF APPLIED
GEOLOGY
ASHUTOSH GOUTAM
M.TECH 1ST SEMESTER
Y18051032
SESSION 2018-19
GUIDED BY :-
PROF. P.K. KATHAL
“GLACIAL FEATURES”

Ice: The Water Mineral
< Ice is solid water (H2O).
< Forms when water cools below the freezing point.
< Natural ice is a mineral; it grows in hexagonal forms.

Formation of Glacial Ice
< Snow is transformed into ice.
= Delicate flakes accumulate.
= Snow is buried by later falls.
= Compression expels air.
= Burial pressure causes melting
and recrystallization.
= Snow turns into granular firn.
= Over time, firn melds into
interlocking crystals of ice.

Forming a Glacier
< Glacier-sustaining elevation is controlled by latitude.
= In polar regions, glaciers form at sea level.
= In equatorial regions, glaciers form above 5 km elevation.
< This elevation is marked by the “snow line.”

Mountain Glaciers
< Flow from high to low elevation in mountain settings.
< Include a variety of types.
= Ice caps cover tall mountain peaks.
= Cirque glaciers fill mountain top bowls.

Mountain Glaciers
= Valley glaciers flow like rivers down valleys.
= E.g. Gangotri Glacier(25km), Siachen Glacier(72km)

Mountain Glaciers
= Piedmont glaciers spread out at the end of a valley.

Movement of Glacial Ice
< Two types of mechanical behavior.
= Brittle – Uppermost 60 m.
 Tension initiates cracking of the ice.
 Crevasses may open and close with movement.
= Plastic – Lower than 60 m.
 Ductile flow occurs in deeper ice.
 Ice flow heals cracks.

< Ice flows downhill via gravity.

< Ice flows downhill via gravity.
= Ice flows away from the thickest part of continental glaciers.
 Analogous to honey flowing away from thickest zone.

Glacial Advance and Retreat
< Zone of accumulation – Area of net snow addition.
= Colder temperatures prevent melting.
= Snow remains across the summer months.
< Zone of ablation – Area of net ice loss.
< Zones abut at the
equilibrium line.

< Toe position.
= If accumulation > ablation, the glacial toe advances.

< Toe position.
= If accumulation < ablation, the toe will retreat upslope.

< Toe position.
= accIfumulation = ablation the toe stays in the same place.

Glacial Effects
< Glaciers are important forces of landscape change.
= Erosion.
= Transport.
= Deposition.

Glacial Erosion
< Glaciers erode substrates in several ways.
= Plucking – Ice breaks off and removes bedrock fragments.
 Ice melts by pressure against the up-ice side of an obstruction.
 Entering cracks in bedrock, this water re-freezes to the ice.
 Glacial movement plucks away bedrock chunks.

Glacial Erosion
< Glacial abrasion – A “sandpaper” effect on substrate.
= Substrate is pulverized to fine “rock flour.”
= Sand in moving ice abrades and polishes bedrock.

Glacial Erosion
< Erosional features of glaciated valleys.
= Cirques.
= Tarns.
= Aretes.
= Horns.
= U-shaped valleys.
= Hanging valleys.
= Roche moutonnée.
= Fjords.

Glacial Erosion
< Cirque – Bowl-shaped basin high on a mountain.
= Forms at the uppermost portion of a glacial valley.
= Freeze-thaw mass wasting into the cirque headwall.
= After ice melts, the cirque is often filled with a tarn lake.
Cirque Glaciers

Glacial Erosion
< Arête – A “knife-edge” ridge.
= Formed by 2 cirques that have
eroded toward one another.
Arête
Horn

Glacial Erosion
< Horn – A pointed mountain peak.
= Formed by 3 or more cirques that coalesce.
= e.g. karakoram range,
Nanda devi, Mt. Kailash

Glacial Erosion
< U-shaped valleys.
= Glacial erosion creates a
distinctive trough.
= Unlike V-shaped fluvial
valleys.

Glacial Erosion
< Hanging valleys.
= The intersection of a
tributary glacier with a
trunk glacier.
= Trunk glacier incises
deeper into bedrock.
= Troughs have different
elevations.
= A waterfall results.

Glacial Erosion
< Fjords.
= U-shaped glacial troughs flooded by the sea.

Glacial Sediment Transport
< Glaciers carry sediment of all sizes – lots of it!
= Some sediment falls onto the ice from adjacent cliffs.
= Some sediment is entrained from erosion of the substrate.
< When glacial ice melts, this material is dropped.

< Moraines – Unsorted debris dumped by a glacier.
= Lateral – Forms along the flank of a valley glacier.
= Medial – Mid-ice moraine from merging lateral moraines.

< Glaciers act as large-scale conveyor belts.
= They pick up, transport, and deposit sediment.
= Sediment transport is always in one direction (downhill).
= Debris at the toe of a glacier is called an end moraine.

Glacial Deposition
< Many types of sediment derive from glaciation.
< Called glacial drift, these include...
= Glacial till.
= Erratics.
= Glacial marine sediments.
= Glacial outwash.
= Glacial lake-bed sediment.
= Loess.
< Stratified drift is water-
sorted; unstratified drift
isn’t.

Glacial Deposition
< Glacial till – Sediment dropped by glacial ice.
= Consists of all grain sizes.
= Also called “boulder clay.”
= Unmodified by water, hence:
 Unsorted.
 Unstratified.
= Accumulates…
 Beneath glacial ice.
 At the toe of a glacier.
 Along glacial flanks.

Glacial Deposition
< Erratics – Boulders dropped by glacial ice.
= These rocks are different than the underlying bedrock.
= Often, they have been carried long distances in ice.

Glacial Deposition
< Glacial marine – Sediments from an oceanic glacier.
= Calving icebergs raft sediments away from the ice.
= Melting bergs drop stones into bottom muds.
= Drop stones…
 Differ from ambient sediment.
 Indicate glaciation.

Glacial Deposition
< Glacial outwash – Sediment transported in meltwater.
= Muds removed.
= Size graded and stratified.
= Abraded and rounded.
< Outwash dominated by sand
and gravel.

Glacial Deposition
< Glacial lake-bed sediment.
= Lakes are abundant in glaciated landscapes.
= Fine rock flour settles out of suspension in deep lakes.
= Muds display seasonal varve couplets.
 Finest silt and clay from frozen winter months.
 Coarser silt and sand from summer months.

Glacial Deposition
< Loess – Wind-transported silt. Pronounced “luss.”
= Glaciers produce abundant
amounts of fine sediment.
= Strong winds off ice blows
the rock flour away.
= This sediment settles out
near glaciated areas as
loess deposits.

Depositional Landforms
< Glacial sediments create distinctive landforms.
= End moraines and terminal moraines.
= Recessional moraines.
= Drumlins.
= Ground moraine.
= Kettle lakes.
= Eskers.

< End moraines form at the stable toe of a glacier.
< Terminal moraines form at the farthest edge of flow.
< Recessional moraines form as retreating ice stalls.

< Drumlins – Long aligned hills of molded lodgment till.
= Asymmetric form – Steep up-ice;
tapered down-ice.
= Common as swarms aligned
parallel to ice flow direction.

< Kettles
= Small depressions in the landscape, often filled with water post glaciation
= Large blocks of ice are left by a retreating glacier
= Outwash sediments deposited around the blocks, possible burial
= Ice block melts, only a void or kettle remains.
= Subsidence and melting can deepen the kettle.
= Kettles lakes are sourced by rainfall or snowmelt.

< Eskers are long, sinuous ridges of sand and gravel.
< They form as meltwater channels within or below ice.
< Channel sediment is released when the ice melts.

Bibliography
• Thornbury, W. D(1985),Principles of Geomorphology, pp. 345-358
• Huggett, R. J.(2007),Fundamentals of Geomorphology, pp. 246-274
• Savindra Singh (2014),Physical Geography, pp. 312-323

Glacial landforms (geomorphology)

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