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Glacial Landforms
Types
Erosional Constructional (deposition)
Erosional Processes
Abrasion Plucking (quarrying)
Factors that influence Abrasion
1. Clean Ice, does not effectively abrade rock;2. Concentration of rock debris at the glaciers
base;3. Supply of new rock; 4. Alla Jay Stravers, ‘Hard tools and Soft beds’5. Basal meltwater, ‘Out with the old in with the
new’ to ‘Out with the fine in with the coarse’6. Velocity, Increased basal sliding will
increase the amount of bedrock abraded per unit time;
Abrasion factors cont.
7. Increased thickness = Increased pressure = Increased abrasion
8. Particle size and texture1. Increased particle size = Increased abrasion2. Increased particle angularity = Increased
abrasion
Glacial striations and grooves
Erosional remnants of linear glacial movements
May be used to interpret pass glacial movement
Hard tools, soft beds Faceted, polished, and striated stones
Plucking/Quarrying
Basal melt water infiltrates fracture and cracks Freezes in place
Plucks rock Entrains the rock in basal ice Transports the rock Work is Done! In more ways than One.
Unloading helps
Helps to produce fractures Plucking tends to be more prominent in areas
where the bed rock is highly fractured
Erosional landforms
Cirques Aretes, Cols, and Horns Glacial Troughs and fjords Paternoster lakes Roches moutonnees
Cirques
Semi-circular hollows set into mountain slopes with steep headwalls
Aretes, Cols, and Horns
Aretes, A narrow knife-edge ridge between back to back cirques
Cols, a topographic low between back to back cirques
Horns, Back to back recession of three or more cirques, (E.G. the Matterhorn in Switzerland)
Arete
Glacial Troughs
Pre-glacial stream valleys, change from V-shaped to U-shaped
Glacial Valley shapes turnout to resemble a parabolic curve
Fjords
Coastal glacial troughs may become submerged with sea water creating fjords.
E.g. Norway, Western British Colombia
C.E. Heinzel
Paternoster lakes
A chain of interconnected small lakes within glacial troughs.
Streamlined forms
Drumlins (Erosional/Depositional?) Roches moutonnees
Drumlins
Drumlins are smooth, oval shaped, streamline hills composed of dense (basal or lodgement) till.
The longer axis is parallel to the path of the glacier and commonly has a blunt nose pointing in the direction from which the ice approached
Drumlins are products of streamline (laminar) flow of glaciers, which molded the sub-glacial floor through a combination of erosion and deposition.
Roches Moutonnees
Have reverse symmetry with respect to drumlins
The upper end is highly abraded, the lower down-glacial ends are craggy and show the signs of plucking.
Ice flow
Ice flow
talus
glacialdrift
30
0m
60
0m
Ice flow
Ice flow
talus
glacialdrift
30
0m
60
0m
Glacial Sediment
Rock debris accumulation Gravity and freeze/thaw processes place rock on
top of a glacier (Mass wasting) Glaciers erode their beds, material is entrained
into the ice and moved. Boulders to Clay
Modes of transport Direct movement from ice Indirect movement from glacial Glaciofluvial (Meltwater) Glacioeolian (loess deposition) Glaciomarine environments Glaciolacustrine environments
Glacial Sediment
Highly variable (Boulders to clay)
Non-stratified Stratified
Non-Stratified Glacial Sediment
Till, Sediment deposited directly from glacial ice Tills are usually poorly sorted and not stratified
Bi-modal particle distribution
Diamictons, are deposits that consist of non-stratified, poorly sorted clasts. So the various types of glacial
Till
Till, close-up
Tills
Varying glacial ice environments tend to produce characteristics Till deposits Glaciomarine/lacustrine Till Lodgement till (sub-glacial deposits) Ablation
Till characteristics Poor sorting Common Bi-modal particle distribution Non-stratified Faceted, polished, and striated clasts Fabric of oriented, parallel, and elongated
particles Compacted Mixed lithologies Deformation of sediment, especially shear
planes and overturned folds.
Stratified Glacial Sediment
Glaciofluvial Glaciolacustrine Glacioeolian
Glaciofluvial (outwash) Glacial meltwater Large fluctuations produce abrupt changes in particle
size; May be distinguished from fluvial deposits near
glaciers terminus; frequent collapse structures Well sorted compared to sediment deposited directly from ice
(Till) May be interbedded with Till May be well imbricated with upstream dips providing good
evidence of current direction (long axes are commonly oriented transverse to the principle current direction.
Commonly braided
Glaciolacustrine deposits
Ice marginal lakes Proximal coarse-grained deltaic sedimentation Distal, continuous fine-grained sedimentation Rhythmites, composed of cyclic silt/clay deposition Varves, believed to represent annual (seasonal?)
couplets
Glacioeolian deposits
Primarily windblown sand, silt, and clay derived from glaciers.
Loess (German for loose), seems to be unequivocally tied to the Pleistocene Successive layers of well-sorted silt and clay (1 to
5m thick) Separated by paleosols or other sediment
Loess in North Dakota
Depositional landforms
Moraines Drumlins Eskers Kames
Moraines
End (Terminal) Lateral Medial Ground
End Moraines
Till (with sand and gravel lenses) deposits that reflect the shape of the glacial terminus
During stable accumulation/ablation ratios vast amounts of sediment are deposited at/near the glaciers front So, End moraine size depends more on the
stability of the glacier terminus than its size If the glacial terminus is advancing it may
form a push moraine.
Lateral moraines
Linear ridges of till formed by the accumulation of rock debris along the sides of a glacier
Till with gravel lenses, coarse-grained, tend to lack the silt/clay rock-flour component
Are typically preserved because they stand above the valley floor, and are not subjected to post-glacial erosion
Medial Moraines
The product of two tributary glaciers meeting Multiple lateral moraines will, Appear as
ribbonlike bands once the glaciers join Poorly preserved, most of the moraine debris
is only surficial.
Ground moraine
Till covered plains of low-relief
Drumlins
Eskers
Elongate, sinuous ridges Sorted and stratified sand and gravel Water worn rounded particles Form near a glaciers terminal zone Formation may occur In linear supraglaical settings, channels,
crevasses Commonly, are thought to be the product of
deposition in ice-walled tunnels
Kames
A suite of stagnant-ice forms The term is generally used to describe
irregular mounds of sand, gravel, and till that accumulated in depressions or cavities in or on a stagnating glacier and dumped chaotically when the glacier melts
May contain, ice walled lakes, kettles or kettle lakes