GLACIATIONS ~ PHYSICAL GEOGRAPHY FORM 5 & 6
GLACIATIONS ~ PHYSICAL GEOGRAPHY FORM 5 & 6
It appears that roughly every 200 – 250 million years in the earth’s history, there have been major periods of ice activity. Of these the most common (recent) and significant occurred during the Pleistocene period of the quaternary area.
In the two million years since the onset of the quaternary, there have been fluctuation in goods temperature of between 50C which have led to cold phases (glaciers) and warm phases (inter glaciers)
CAUSES OF ICE AGE/ THEORIES
-Variation in support activity may increase or decrease the radiation coming on earth.
-Injection of volcanic dust into the atmosphere can reflect and absorb radiation from the sun changes in atmospheric carbon dioxide gas could concentrate the green house effects (absence of carbon dioxide.
-The movements of Planets either into colder latitudes or at constructive margins where there is an increase in altitude could lead to an overall drop in world land temperature (high latitude low isolation.
-Changes in ocean currents or jet streams.
-Changes in atmospheric carbon dioxide gas could concentrate the green house effect
SNOW ACCUMULATION AND ICE FORMATION:
-As the climate gets colder more precipitation is likely to be in the form of snow in the winter and there is less time for that snow to melt in the shorter summer.
-If the climate continuous to deteriorate, snow will be falling throughout the year forming a permanent snowline. (The level above which snow will lie throughout the year).
-In the northern hemisphere the snow line is at a lower altitude on north facing slope and these receive less isolation (sun rays) than south facing slopes.
-Where snow collect in hollows it becomes compressed by weight of subsequent falls and gradually developed into more compact, dense form called firm or nerve.
.Firm is compacted snow which has experienced one winter freezing and survived for summer’s melting.
-It is composed of randomly oriented ice crystals separated by air passed.
-In the temperature latitudes such as in the Alps, summer melt water percolates into the firn only to freeze either at night or during the following winter forming an increasing dense mass.
-Air is progressively squeezed out and after 20-40 years the firm will have turned into solid ice.
-This same process may take several hundreds of years in Antarctica and Greenland where there is no summer melting.
-Once has formed it may begin to flow downhill under the force of gravity as glacier.
GLACIER AN ICE MASSES
-Glaciers may be classified according to size and shape characteristic which are relatively easily to identify by field observation. These are,
LANDFORMS PRODUCED BY GLACIAL EROSION
-Very small and occupy hollows and gulley on north facing slopes in the northern hemisphere
2. Corrie or cirque.(highland glacial erosion features.
-Although larger than niche glaciers are smaller masses of ice occupying arm – chair shaped hollows in mountains. They often over pill from their hollows to feed valley glaciers.
-These are armchair – shaped hollows with a steep back wall and a rock basin. They are known as corries in Scotland.
3.Arêtes.(highland glacial erosion features)
-When two adjacent cirque erode backward or sideways toward each other the previously rounded landscape is Transformed into a narrow, rock steep side ridges called an arête, example Alps in Switzerland.
-If there are three or more cirques all side of a mountain a pyramidal peak or horn may be formed.
-This feature has steep side and several arête radiating from the central peaks.
-When either cirque is combined together can form pyramidal peak.
5. Truncated spurs
-Formed by meanders in the low lands, where by the rate of erosion has decreased and the rocks are hard and at the end form alluvial fans.
-Spurs whose ends have planed off due to erosion on the process of straightening the valley as it moves down the valley (highland glacial erosion feature).
6. Crag and tail (lowland glacier erosion features)
-This consists of a larger mass of resistant rock or crag (e.g. Basaltic rock crag upon which Eden burgh has been built).
-High pressure where is small area and low pressure is large area.
7. Roche mountaineer. (Lowland glacier erosion feature)-
-An outcrop of resistant rock which rise above the plain smoothed by ice on the upstream by abrasion and plucking processes. This feature also occurs in glaciated highlands.
An outcrop of resistant rock smoothed by a glacier on the upstream side into a gentle slope. On the downstream side the glacier erodes by plucking to give steep and jagged (rugged) slope (lee).
Example: Mobuku Valley in the Ruwenzori mountains,Yosemite National Park in California,on the slope south of Mawaza along Mt.Kilimanjaro.
8. U-shaped valley/glacial trough. (Highland erosion features)
-It is a steeply sided flat-bottomed wide glacial valley. Develop from a river valley in which glacier had covered. Some contain features formed by both glacial erosion and deposition.
– At initial stage the valley occupied the V- shaped valley but because of continuous glacier erosive activities. The valley was more enlarged by being more deepened and widened becoming more opened and known as U-shaped valley.
9. Hanging valley.
-It is a tributary valley that ends abruptly above the floor of a U-shaped valley and separated from it by almost a vertical slope.
-The rate of erosion is much greater at the main glacier valley than on the tributary valley, after glacier have retreated the floor of the main glacier valley lies far below than the floor of a tributary valley making the tributary valley to hang by ending a abruptly above the valley.
-A river occupying a hanging valley will fall more abruptly into the main valley to form waterfalls and produce alluvial fans.
10. Rock basin (highland erosion features)
– It is an irregular depression of the floor of glacial valley formed by unequal glacier upon the bedrock.
– This develops when weight and thickness of glaciers increase after two glacial have joined together.
– After glacier melts, rock basin becomes the site of lake. These are known as rock basin lakes.
11. Ribbon lake (Finger Lake or Trough Lake).
– Is a lake that occupies an elongated trough or hollow excavated by ice on the floor of a u-shaped valley E.g. lake Michelson near Mt. Kenya (Highland erosion features)
12. Fiord. (Highland erosion feature)
– It is a long, narrow, deep in let depression steeply sided into the sea. Fiords were formed when glaciers make the way to the sea.
– Most of the fiords occupied by deep sea water after the coastal land submerge due to ice melting forming natural harbours e.g. the also fiord of Norway.
13. Ice eroded plain. (Lowland glacier erosion)
– It is an extensive and almost level lowland area of bare rocks .It was once covered by an ice sheet which smoothed the topography and produced large area of bare rocks.
GLACIER TRANSPORTATION AND DEPOSITION
Glacier movement can also result into the formation of depositional features such as;
1) Moraines. (Highland (alpine) deposition features) unsorted materials.
Are the unsorted fragments of different size and shape that have been eroded, transported by glacier and then deposited in ridges within the glacial valley.
Types of moraines based on area within the glacier valleys where materials have been deposited;
a) Ground moraines – Formed at the bottom of glacier valley.
b) Medial moraines– Formed at the point where two glacial valleys meet
Adjacent lateral moraines joined and are carried as a single long ridge of till.
c) Lateral moraine – Formed along side of the glacial valley. (Ridge like piles of till along the sides of glacier).
d) Terminal moraine– Occurs at the end of glacial valley as the materials had been accumulated.
– Terminal moraines are built up when glacier is stationary.
– Materials of terminal moraines can be carried down the valley by melt water and deposited to form a feature known as outwash plain.
e) Recessional moraines – The end moraines built while the glacier is retreating. (A series of roughly parallel terminal moraines that make the step by step retreat of the glacier).
2) Boulder clay plain. (Lowland glacial deposition)
(Till plain)- Is an extensive lowland (plain) area consisting of clays and boulders deposited randomly by ice sheet and burying vast area of land.
3) Erratics are large boulders made of rock, different from that of the region where they are deposited
4) Drumlins (unsorted materials) (lowland glacier)
They are elongated oval shaped hill that are made of clay and boulders as they were deposited irregular on a till plain (boulder plain). They occur in groups and aligned in one another.
5) Eskers (lowland) (sorted fluvial – glacial material)
– Long, steep sided ridge of course sands and gravels.
– Formed when ice remain stationary for long time. Streams form permanent sub glacial in which materials consolidate and compact if ice melts the materials are left as ridges which referred to eskers.
– Is an irregular mound or hill (mass) of stratified materials (sand and gravel)
– Kames vary greatly in shape and size and occur in isolation or large groups. They form as ice deposited materials randomly.
7) Out wash plain (lowland)
– It is a wide gently sloping low lying land of gravel and sand at the end of an ice-sheet.
– Out wash plain is usually found after boulder clay plain.
Value/importance/significance of glaciated land escapes to human being.
1. Some glaciated landscape like that of boulder clay plain and others are good for agriculture.(fertile)e.g. Dairy belt in U.S.A also crop cultivation in old glacier lakes e.g. wheat cultivation in Canadian prairies.
2. Hanging valleys are suitable for HEP generation. E.g. Norway, Sweden and Switzerland produce great proportional of hydro electricity by utilizing waterfalls of hanging valleys.
3. Glaciated landscapes provide attractive scenery also the glaciated highlands and peaks e.g. Mt Kenya and Kilimanjaro attract tourists.
4. Many glaciated valleys are used as grazing land as they contain good pastures. They are used for animal grazing main in summer season .e.g. In the Alps in Europe.
5. Fiords form natural harbors e.g. Oslo ford in Norway and also fishing-grounds.
6. Glaciated landscape contains a number of lakes which are used for navigation e.g. great lakes in N. America.
7. Melting of glaciers give rise to rivers. The rivers can be utilized for domestic and industrial purposes.
Disadvantages of glaciated landscape
1.The boulder clay plain in some regions, have produced a mainly landscape which have little or no value to agriculture e.g. central Ireland.
2.Many out wash plains contain infertile sands which give rise to extensive areas of waste land.