GLACIAL ACTION

WEEK 5

SUBJECT: GEOGRAPHY

CLASS:    SS 2    DATE: ………………………. TOPIC:    GLACIAL ACTION

CONTENT:

(1) Action of glacial in temperate region

(2) Features of glacial erosion in the highland areas (3) Glacier erosion in lowland

(4) Economic importance of Glacier Features

SUB-TOPIC 1: ACTION OF GLACIER IN TEMPERATE REGION

Action of glacier is an important agent of erosion, here, transportation and deposition of materials is confined to mountains and temperate regions of the wind.

TERMS ASSOCIATED WITH GLACIERS

1. ICE: This refers to the solid form of water, formed as a result of freezing when the temperature is continually below 00C.
2. GLACIER (moving ice): This implies very large accumulation of ice, (either a frozen sea or river) in motion.

iii. GLACIATION: This is referring to the wearing away of the earth surface by large accumulation of ice in motion (glacier).

1. SNOW: This is frozen water vapour which falls in form of crystal through the atmosphere. v. SNOW LINE: This implies the lower limit of perpetual snow cover on the mountain.
2. SNOW FIELD: This is the region that is permanently under snow cover.

It is important to note that Glaciations generally gives rise to erosional features in the highland and depositional features on the lowlands.

ACTION OF GLACIER EROSION

1. SAPPING: Sapping is the breaking up of rocks of alternate freezing and thawing of water at the bottom of cracks between a mass of ice and the sides and floor of a valley or the sides of a mountain.
2. PLUCKING: By plucking, the glacier freezes the joints and beds of the underlying rocks tears out individual blocks and drags them away.
3. ABRASION: By this, the glacier scratches, scrapes, polishes and scours the valley floor with the debris frozen into it. These fragmented debris are powerful tools of erosion (denudation).

EVALUATION

1. Highlight the various terms associated with glacier. 2. Mention three actions of glacier erosion.
2. Discuss two of the actions mentioned in 2 above.

SUB-TOPIC 2: CHARACTERISTIC FEATURES OF GLACIER EROSION IN THE HIGHLAND 1. STRAITION: Striations are scratches left on rocks over which glacier passes. The rock fragment (of

different shapes and sizes) embedded in the glacier affects striation of rocks.

2. CORRIES OR CIRQUE: This is a deep and rounded hollow or depression with steep side form as a result of the downside movement of a glacier from it snow cover valley head, and intensive shattering of the upland slope. They are arm chair hollows, resulting from the plucking of rocks materials down the slope when the ice finally moves; it will form a lake, called CORRIE LAKE OR TARN.
3. ARETE: When two corries cut back opposite side of the same mountain, forming a knife – edge ridge in between is known as Arête. Hence Arête is a ridge like structure separating the two corries.
4. PYRAMIDAL PEAK: When a mountain has three or more corries basins around its flanks, erosion will cut back corries and with time a pinnacle will be formed which is shaped like a pyramid, and this is called pyramidal peak, a typical example is the Swiss-Italian border. The diagram below illustrates corries, arête and pyramidal peak

Cirque, arête and Pyramid Peak

5. BERGSCHRUND: Bergschrund is formed near, or at the head of glacier. It is a deep and vertical crack separating the lower part of the glacier that has started moving down its valley and the upper part which is static. This actually takes place during summer when ice begins to move out of the corries down the mountain valley. As the glacier moves, small-scaled cracks also develops as glacier negotiates a bend along its valley such cracks are called CREVASSES. Bergschrund is derived from German, and Rimaye in French.
   

Bergschrund

6. U-SHAPE VALLEY OR TROUGH: This is a wide, flat floor with very steep side which has been eroded by glacier. All the sides and floors including all debris are washed away by glacier. This results in the formation of a U-shaped valley which forms the main valley.
7. HANGING VALLEY: This is formed when glacier action from tributaries erodes materials into the main or U-shaped valley. It can be used for the generation of Hydro-Electric Power (H.E.P)
8. ROCK BASIN AND ROCK STEP: When two tributaries join a main valley, the additional weight of ice in the main valley cuts deeper into the valley floor at the point of convergence, thus forming a rock step. It can also be formed due to differences in resistance to frost action. On the other hand rock basin is formed when glacier erodes and excavates the valley floor so deep to form a rock basin.
9. MORAINES: Glacier moving down the valley sweeps away everything in its way – stones, soil and fragments of rocks loosened by frost action, all these materials are called moraines. But because of the movement of glacier, the materials adopt certain shapes which are found when the ice has melted; this then becomes the different types of moraines. These include:

(a)    MEDIAL MORAINES: These are lines of stones and rock found in the middle of a valley or when two lateral moraines join or collapse.

(b)    LATERAL MORAINES: These are lines of stones and rocks found at the side of the valley. (c)    GROUND MORAINE: This is the material which is found at the bottom of the glacier.

(d)    TERMINAL MORAINE: This is moraine found lying where the ice ends its journey either temporarily or finally.

EVALUATION:

1. Briefly explain the following (i) U-shaped valley (ii) bergschrund (iii) hanging valley (iv) lateral moraine (v) terminal moraine.
2. With the aid of an annotated diagram, describe the following (a) pyramidal peak (b) corries (c) arête

SUB –TOPIC 3: GLACIER EROSION IN LOWLANDS Erosional features of glacier which occur in lowland areas include:

1. ROCHE MOUTONNEE: This is a resistant residual rock structure. The surface is striated by ice movement. Its downstream side is smoothed by abrasion and roughened as a result of plucking and it is usually much steeper. Rock moutonnee are found in both highland and lowland glaciated region.
2. CRAG AND TAIL: Crag is a mass of hard rock which protects the softer leeward slope from being completely worn down by the oncoming ice. It has a gentle tail, strewn with eroded rock debris. A classic example is the Castle Rock of Edinburgh, Scotland.
   

Crag and tail CHARACTERISTICS FEATURES OF GLACIER DEPOSITION IN LOWLAND

1. BOULDER CLAY: Boulder clay is the ground moraine of the glaciers. It generally consists of stones of various sizes and shapes in a mass of sand and clay. Some examples of boulder clay include East Anglia and the Northern Mid-West of USA and this form the rich arable lands.
2. ERRATICS: These are transported rock fragments which are composed of materials entirely different from bedrock or rock fragments of the region which they are deposited. They are deposited when the ice carrying them melts into water. They abound in both lowland and highland areas of Europe e.g. Silurian grits are found perched on the carboniferous limestone of the Pennines. They hinder farming where they are found in large numbers.
3. DRUMLINS: These are swarms of oval, elongated wale-back hummocks composed wholly of boulder clay, with their elongation in the direction of the ice flow that is on the downstream side. The shape of drumlins is better described as basket of eggs. Drumlins are found in country down in Northern Ireland and glacier plains around the Great Lakes in North America.
4. ESKERS: These are long, narrow, sinuous ridge composed of sand and gravel which mark the former sites of sub-glacier melt water; they vary from a few meters to 60m in height and may be several kilometreslong. Eskersare found in somepartsof USA and Scandinavia e.g. Punkaharju EskerofFinland.
5. TERMINAL MORAINES: These are made up of coarse debris deposited at the edge of the ice sheet, to form hummocky and hilly country. Example of this is the Baltic Heights of the North European Plain.
6. OUTWASH PLAINS: These are made up of fluvio –glacial deposits washed out from the terminal moraines by the streams and channels of stagnant ice mass. The melt – waters sort and re-deposited the materials in a variety of forms from the low hilly heathlands. An example is the Luneburg heath of the North European Plain.

ECONOMIC IMPORTANCE OF GLACIER FEATURES:

1. They provide glacier lakes which are of real value to man by providing natural route ways as those of the Great Lakes of North America.
2. Hanging valley sometimes provides water falls which are suitable for the developments of Hydro–Electric Power. Examples are those of Norway and Switzerland.
3. The glaciated regions offer services as tourist centres.
4. Boulder clay plains are sometimes very fertile, examples include; East Anglia in Great Britain and parts of the Dairy of North America.
5. Old glaciated lakes beds are invariably fertile; they owe their properties to the rich alluvial deposits which collect on the floors. Example is the Canadian prairies in North America.

EVALUATION

1. With good examples and locations describe the following (a) Terminal moraine (b) esker (c) drumlins (d) boulder clay.
2. Mention four economic importance of glacier features to man. GENERAL EVULATION
3. Account for the economic importance of glacial features to man.
4. Briefly explain the following: i. Bergschrund ii. Medical moraine iii. Lateral moraine iv. U-shape valley v. Hanging valley

WEEKEND ASSIGNMENT Objective Test

1. Which ofthe following termsisnotassociated with glacier(a)corrosion (b) snow (d)snowfield (d) snowline
2. The breaking down of rocks of alternate freezing and thawing of water at the bottom of the cracks; is associated with ———— (a) plucking (b) abrasion (c) sapping (d) cracking.
3. Another name for Corrie Lake is (a) tern (b) torn (c) tarn (d) torn.
4. Which glacial feature is found in the Swiss, at the Italian border? (a) Corrie (b) Arête (c) Pyramidal peak (d) U-shaped valley
5. Moraine can be divided into ———– (a) 5 (b) 3 (c) 4 (d)2
6. Moraines are best described as (A) pieces of rocks embedded in the glacier and brought down the valley (B) unsorted glacial deposits comprising a wide range of eroded materials (C) ice in motion (D) long, narrow ridges of sand which mark the former sites of sub-glacial meltwater streams (E) glacial troughs which become filled with water after the disappearance of the ice.

ESSAY QUESTION

1. Describe the following: (i) Arête (ii) U-shape valley (iii) Moraine READING ASSIGNMENT

Read on the action of wave in your Geography textbook. REFERENCES TEXTS

1. Certificate physicaland Human Geography forSeniorSecondary Schools (New Impression)by O. Areola, K. Ahmed, O.I. Irueghe, B.O Adeleke and G.C. Leong.
2. Comprehensive Geography for Senior Secondary Schools (New Edition) by P. Oluwafemi, and S. Ajayi. 3. Essential Geography for Senior Secondary Schools by O.A. Iwena.