GC Leong Test: Landforms Of Glaciation - 2 for UPSC Indian Geography

Crag and Tail: The crag is a mass of hard rock with a precipitous slope on the upstream side, which protects the softer leeward slope from being completely worn down by the oncoming ice.

It, therefore, has a gentle tail, strewn with the eroded rock debris. The classic example is the Castle Rock of Edinburgh, Scotland.

Edinburgh Castle is located on the crag and the High Street on the tail.

• They are called erratics because they are composed of materials entirely different from those of the region in which they are found. Such erratics are thus most useful in tracing the source and direction of the ice movement.

• Sometimes the erratics may be found perched in precarious positions just as the ice dropped them and they are then termed perched blocks.

• Examples of such blocks are commonly encountered in both lowland and highland areas in Europe, e.g. Silurian grits are found perched on the Pennines' Carboniferous Limestone. Their presence in large numbers is a hindrance to farming.

Roche moutonnée are streamlined rock knolls formed where moving glacial ice passes over exposed bedrock. Their upstream or stoss side is smoothed by abrasion, while the downstream or lee side is steep and rough due to plucking.

Because their formation requires moving ice over bedrock (not a specific elevation), they occur wherever glaciers eroded bedrock surfaces. This includes both highland glaciated regions (for example, parts of the Scottish Highlands) and lowland glaciated regions (for example, areas of the Canadian Shield and parts of Scandinavia).

Therefore, Roche moutonnée are correctly recorded as occurring in both highland and lowland glaciated regions; option C is the correct choice.

Boulder clay or glacial till:

• This is an unsorted glacial deposit comprising a range of eroded materials -boulders, angular stones, sticky clay and fine rock flour.

• It is spread out in sheets, not mounds, and forms gently undulating till or drift plains. The landform is rather monotonous and featureless.

• The degree of fertility of such glacial plains depends very much on the composition of the depositional materials. Some of the boulder clay plains such as East Anglia and the northern Mid-West of U.S.A. form rich arable lands.

The correct answer is Option A - Drumlins

Drumlins are streamlined hills composed mainly of glacial till formed beneath moving ice; their long axis is aligned with the direction of ice movement.

They characteristically have a steeper upstream (stoss) side and a gentler downstream (lee) slope, occur in groups called drumlin fields, and commonly measure from a few metres up to about 50 m in height with lengths of up to 1-2 km.

The form and orientation result from deformation and deposition of till and/or sculpting by the flowing glacier, which produces the distinctive streamlined shape.

• Eskers - are long, sinuous ridges of stratified sand and gravel deposited by subglacial meltwater channels; they differ from drumlins in composition and origin.
• Terminal moraines - are ridges of unsorted debris deposited at the former snout of a glacier; they mark positions of ice margin deposition rather than streamlined subglacial shaping.
• Outwash plains - are broad, flat areas of stratified sediments laid down by meltwater beyond the glacier front; their morphology is depositional and planar, not elongated hills aligned with flow.

Terminal moraines are formed by glaciers. When a glacier (or ice sheet) moves forward, it carries along rock fragments, soil, and other debris. At the edge (terminus) of the glacier, this material gets deposited as the ice melts.

Thus, terminal moraines consist of coarse debris accumulated at the edge of an ice sheet or glacier, marking the farthest advance of the ice.

Outwash plains: These are made up of fluvioglacial deposits washed out from the terminal moraines by the stagnant ice mass's streams and channels.

• The melt-waters sort and redeposit the material in various forms from the low hilly heathlands, such as the Luneburg Heath of the North European Plain, to undulating plains terraces, alluvial fans and deltaic deposits of the melt-water streams make up the landscape.

• Kames, small rounded hillocks of sand and gravel may cover part of the plain. The deposition takes the form of alternating ridges and depressions, the latter may contain kettle lakes and give rise to characteristic 'knob and kettle' topography.

• Soils that do exist are so thin that they are incapable of supporting effective agriculture.

• Glacial drifts in the valleys and benches or alps which were not affected by glaciers have good pastures during summer.

• Cattle are driven up to graze on the grass and return to the valley bottom in winter. This form of animal-migration type of farming is called transhumance.

• Morainic deposits may dam, or glaciers may hollow out, lakes which greatly inconvenience large scale farming or land development.

• But when the lakes are eliminated, the old glacial lake beds with their rich alluvium support heavy cropping

• Though the Ice Ages were at their height over 30,000 years ago, the effects of glaciation on both landforms and human activities profoundly influence many parts of the world today.

• Their most striking impact is felt in the temperate regions of Europe and North America which were once under continental ice sheets.

• Further south and on the high mountains worldwide, slow-moving glaciers are still shaping the landscape in the Alps, Andes, Rockies and Himalayas.

• Glacial influences on Man's economic activities are both favourable and unfavourable, depending on the intensity of glaciation, the region's relief, and whether the effects are of an erosional or depositional nature.