LANDFORMS CREATED BY GLACIER

THE WORK OF MOVING ICE :

SOURCE : NIOS & NCERT

SNOW – FIELDS :

• Wherever the rate of snow melting or its evaporation is lower than the rate of snowfall in a year, snow accumulates into great mass of ice.

• Permanently snow covered regions of this type are called snow ­ fields.

• Snow ­ fields occur in polar regions and on high mountainous areas.

• Snowfields are always found above the snow line.

• Snow line is an imaginary line above which there is permanent snow.

• The height of the snow ­ line is not uniform and is affected by latitude, amount of snowfall, direction of winds and slope.

GLACIER :

• A moving mass of ice and snow is called a glacier.

• Its velocity is very low and it moves from a few centimetres to a few metres in a day.

Types of Glaciers :

(i) continental glaciers and

(ii) valley glaciers.

(i) Continental Glaciers:

• A thick ice sheet covering vast area of land is called a continental glacier.

• Glaciers of this type build up at the centre and move outward in all directions.

• Continental glaciers of today are found mainly in Antarctica and Greenland.

• The precipitation in these regions occurs in the form of snow.

 (ii) Valley Glaciers :

• When a mass of ice from the high mountainous regions starts moving down into the pre-existing valleys, it is called a valley glacier or a mountain glacier.

• The shape of the valley glaciers depends on the valley it occupies.

• Where the valley is broad, the glacier spreads outwards and where the valley is narrow, the glacier contracts.

• The longest glacier in India is the Siachen Glacier in Karakoram range which is 72 kilometres long.

• Gangotri Glacier in Uttarakhand is 25.5 kilometres long.

• The two important rivers of India, the Ganga and Yamuna, originate from Gangotri and Yamunotri glaciers respectively.

LANDFORMS PRODUCED BY GLACIER :

(A) Erosional work of glacier :

• As a glacier moves over the land, it drags rock fragments, gravel and sand along with it.

• These rock fragments become efficient erosive tools. With their help glacier scrapes and scours the surface rocks with which it comes in contact.

• This action of glacier leaves behind scratches and grooves on rocks.

The landforms created by glacial erosion are:

I. Cirque (or Corrie), (firn):

• Snow collects at the upper end in a bowl shaped depression, is called cirque.

• Layers of snow in the process of compaction and recrystallization are called firn.

• Sometimes the deepest parts of these hollows are occupied by accumulated ­water, to form Corrie Lake (or Tarn).

II. ‘U’ ­ shaped Valley:

• The glacier does not carve a new valley like a river but deepens and widens a pre-existing valley by smoothening away the irregularities.

• In this process the glacier broadens the sides of the valley.

• The shape of the valley formed in this manner resembles the letter ‘U’.

• Such a valley is relatively straight, has a flat floor and nearly vertical sides.

III. Hanging Valley :

• Just like tributary streams of river, there are tributary glaciers also which join the main glacier after moving over their mountainous path.

• These tributary glaciers like the main glaciers carve U ­shaped valleys.

• However, they have less volume of ice than the main glaciers and thus their rate of erosion is less rapid.

• As a result their valleys are smaller  and not as deep as that of the main glacier.

• Due to this difference in deepening; the valley of the tributary glacier is left at a higher level than that of the main glacier.

• The valley of the tributary glacier just looks like hanging downwards at the point of its confluence with the main valley.

• This type of a topographical feature is called a hanging valley.

• This feature is visible when ice has melted in both the valleys.

• When the ice in the hanging valley melts, a waterfall is formed at the point of confluence of this stream with the main river.

Iv. Eskers :

• Glaciers can also contain sinuous flows of meltwater that occur in ice tunnels at the base of the ice.

• The beds of these sub­surface glacial streams are composed of layers of sand and gravel.

• When the ice melts from around the meltwater tunnels, the beds of sand and gravel are deposited on the Earth's surface as long twisting ridges known as 

eskers.

V. Drumlins :

• feature of continental glaciation are hill shaped deposits of till known as drumlins .

• A couple theories exist to explain their formation.

• The most excepted theory suggests they form when saturated ground sediments oozes up into hollows at the base of an advancing glacier.

• The sediment is then stretched out and moulded into a streamline form as the ice moves forward.

VI Kettle hole :

• When glaciers are rapidly retreating, numerous blocks of ice can become detached from the main body of the glacier.

• If glacial drift is then placed around the ice, a depression on the surface called a kettle hole can be created when the ice melts .

• Kettle holes are commonly found on moraine and outwash plain deposits.

VII.Outwash plain :

• Outwash deposits are formed when sand is eroded, transported, and deposited by meltwater streams from the glacier's snout and nearby till deposits to areas in front of the glacier.

• Outwash plain develops when there are a great number of meltwater streams depositing material ahead of the glacier.

VIII.Kame :

• Glaciofluvial deposits are also associated with the melting of stagnant ice at the front of the glacier.

• Where sediment rich water flows into a crevasse or depression in the ice, a conical shaped pile of sand and gravel, known as a kame .

(B) Transportation work of Glacier :

• Although the glacier moves very slowly, it drags with it large boulders and rock fragments.

• Glacier gets this material from the mountain slopes, valley sides, valley bottom and from air.

• This material is called the load of glacier.

(C) Depositional work of Glacier :

• When the glacier melts or retreats, it deposits its load in different parts.

• The debris thus deposited are called moraines. Depending upon their location in the valley.

Types of moraines:

(i) Terminal Moraine :

• When the glacier melts, the debris are deposited at the end of the valley glacier in the form of a ridge.

• Morainic material ranges from fine clay to large angular boulders.

(ii) Lateral moraine:

• The moraine which is deposited on either side of a glacier is called lateral moraine.

(iii) Medial moraine:

• When two glaciers join each other their lateral moraines also join.

• Moraines thus formed on the confluence of two glaciers are called medial moraines.

(iv) Ground moraine:

• It consists of deposits left behind in areas once covered by glaciers.

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