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