This refers to that stage where moist particles of air-cool and condense into snow at temperatures below 0^oC or 32^oF. A glacial period is when snow and ice are formed and eventually transformed into moving ice.

A glacial phase is when climatic change takes place such that temperature raise and bring about meting of ice and snow. Glacial scenery dates from periods in geological history when large areas were covered by glacial and ice sheets.

A glacier

A glacier is a mass of ice that is largely confined within a valley or a glacier is a mass of ice flowing out of snowfield under the influence of gravity or due to pressure of overlying snow, which caused the ice beneath to move or be expressed out wards from the center of the snowfield.

Snow is composed of minute ice crystals separated by air spaces. Permanent glaciers exist in all continents except Australia. The level latitude) at which permanent glaciers occur above sea level is known as the snow line. The height or altitude of the snow line varies from place to place.

FORMATION OF GLACIERS

When air temperature falls below 0^oc, water vapour in the atmosphere condenses to form ice crystals, which fall to the earth as snow. If temperatures remain below 0oc snow gradually accumulates. Fresh-fallen (snow flakes) which contain trapped air making it white and fluffy in appearance (like cotton wool). As more snow falls on the....................underlying layers, the pressure forces some air to escape, leading to melting and re-freezing and the snow re-crystallizes and becomes compact, though it still contains some air and is still white (firn or neve?).

Further compaction causes the remaining air to escape and the snow re-crystallizes into a hard, granular ice with a glassy appearance called a glacier ice. When this glacier ice flows outwards or down slope from the snowfield it is known as a glacier (moving ice).

TYPES OF GLACIERS

There are several ways of classifying glaciers. Some scholars classify them according to location and characteristics while others according to size and shape. Some others use a temperature. However, glaciers fall into three main types:

(a) Valley glaciers (also known as Mountain or Alpine glaciers). These are found on Mountains and occupy pre-existing river valleys. They are induced to move down slope by gravity. Glaciers in East Africa are of this type.

(b) Ice sheets ice cap (Continental glaciers). These are broad and cover the entire landscape. They occupy and over spread continental or plateau areas. Attraction and green land are the only surviving examples of ice sheets. Smaller plateau ice sheets such as Axel Auberry island in Arctic (Canada) and Spits in Bergen in N.W. Europe do exist.

( c) Piedmont glaciers. These consist of sheets of ice, which are formed when several valley glaciers coalescent lower ground usually at the foothills of the mountain areas to form huge lakes of ice.

A. Movement of glaciers.

There are two types of glacier movements. These are: (i) Gravity flow

(ii) Extrusion flow.

Gravity flow.

This takes place through the following ways:

- Plastic flow (Rheidity)

- Inter granular translation

- Regelation

- Basal slip (shear or laminar flow).

Plastic flow (Rheidity). According to this mechanism, ice behaves as an elastic and brittle solid, and if internal stress acts on it for sometime, it flows like a highly viscous liquid, i.e. it becomes deformed.

Regelation. In this mechanism, pressure exerted by the weight of the overlying ice, causes melting if it is sufficient. The liberated water flows down slope and solidifies where pressure is less. As more water flows, and solidifies down slope, the glacier gradually extends forward

Inter granular translation. In this mechanism, ice crystals or granules slide over and against each other due to pressure from overlying ice. The sliding is made easy by melt water from regelation above, which provides lubrications. As more granules move and solidify down slope, the glacier extends forward.

Basal slip (shear or laminar flow). In this mechanism, the glacier slides against the bed rock. The sliding is made easy by lubrication provided by melt water from regelation, overlying layers or strata of ice also slip and slide over each other along their bedding planes, with the greatest slipping at the top. This results into the shearing of the ice.

Mechanisms of gravity flow:

Extension flow. In this flow, further accumulation of snow on the snowfield causes a sideways displacement of the ice in all directions like thick porridge poured on a flat surface. As more porridge is poured out on the flat surface, the edges or margins are displaced radically outwards.

Factors that control glacier movement. There are a number of factors, which control flakier movement. These include the following

(i) Load. Glaciers carrying more debris are slower. Load increases internal friction within the flakier, and friction between the glacier and bedrock or valley sides.

(ii) Temperature. Glacier movement is faster in warm (temperate) glaciers than in cold (Polar) glacier. The reason is that in warm glaciers, basal slippage is more due to the more melt water available. Glaciers whose temperatures are below 10oc are known as cold or polar glaciers, while those with high or temperatures are known as warm or temperate glaciers.

(iii) Steepness of slope (gradient). The steeper the slope, the faster the rate of movement and the gentler the slope, the slower the speed of movement.

(iv)Glacier thickness. Rate of glacier movement also increase with thickness. Thick glacier move further than these ones.

The work of Glaciers. As the ice moves from the mountaintop to the valley, it becomes one of the agents of erosion. It also transports and deposits like a river. Therefore glaciers are one of the main agents of landform evolution.

Glacial erosion. A glacier, especially one that is carrying debris can remove and carry a lot of materials, thus drastically changing the landscape. A glacier has the advantage of being able to melt and refreeze in order to overcome obstacles in its path. This melting and refreezing enables the glacier to be effective in eroding materials along its path.

B. Processes of glacial erosion

A glacier erodes in two main ways:

(a) Plucking and Quarrying. Plucking is the process in which the glacier freezes on rocks protruding on its valley bed and sides. As the glacier advances forward, it tears out blocks of rock, which are then removed and carried along. Plucking involves both vertical pressure y the overlying ice and also the downhill drag by flakier advance. It may well create stresses in the rock, thus enlarging existing joints and even creating new ones in little jointed rocks thus stimulating freeze and then activity. Plucking results into a jagged surface such as can be seen on the leeward sides of Rock Mountains.

(b) Abrasion (Corrosion) is the sand papering effect of the debris

Moraine being carried by the glacier. Materials frozen at the bottom or on the sides of the glacier scrape grind and scratch the rock surface on which it is being dragged. Therefore the glacier uses its debris as a tool by which it polishes, scours and scratches and creates striation on the surfaces over which it passes.

Glacial erosion produces debris known as Moraine, which consists of an assortment of fragments of various sizes.

( c) Freeze - thaw frost shattering sapping. This process is an equally important process by which glaciers do shape landforms, in glaciated areas. On frost shattering, Mountain peals and ridges, which project above the ice like Mt. Stanley, and Mr. Baker. On Ruwenzori and Nelion on Piggott's Peak on Mt. Kenya, are shaped by freeze - thaw, (sapping).

The process operates as follows:

Water melts from the snow and ice and enters the rock cracks during the day. At night it freezes and expands. The expansion of the ice shatters the surrounding rocks when the pieces of broken rock fall around the peaks the form felsenmeer and when they fall on the glacier they become part of Moraine.

Transportation glaciers.

Moraines transport their moraine in several ways. These include:

(a) On the sides of the glacier. Materials broken by fross shattering, or got from mass wasting on the valley sides fall and concentrate on the sides of the glaciers. Then the flakier sides become lined with long ribbon of Moraine. Such Moraine transported on the sides of the glacier is known as lateral moraine.

(b) In the top-middle of the glacier. When two adjacent glaciers join, their lateral moraines closest to each other unite to form middle moraine on top of the glacier. Such middle moraine is known as medial moraine.

( c) At the snout (Tongue or ice front) of the glacier. As the glacier snout advances, it pushes along an arcuate mound of debris, which is called a terminal moraine.

(d) Within the glacier. Some of the material on the surface of the glacier (lateral and medial moraines) soon fall into crevasses and become enclosed within the glacier. Material enclosed within the glacier is known as englacial moraine.

(e) At the bed (bottom) of the glacier. A certain proportion of englacial moraine may reach the bottom or bed of the glacier. Together with material scraped or plucked from the bed of the glacier, it makes up sub glacial (bed or basal moraine).

C. GLACIAL LANDFORMS

(a) Erosional Features. In East Africa they are confined to the highlands in Mts. Kenya, Ruwenzori and Kilimanjaro.

(b) Cirques (corries). This is a deep rounded depression on the side of the Mountain with steep sides created by erosion of ice. It also has a shape of an armchair. The word cirque is a French word-meaning circle (though not fully enclosed).

Cirques are formed when snow accumulates in a depression on a mountainside, or a valley head. The main process responsible for the formation of cirquet is frost shattering/alternating freeze-thaw/sapping. The alternating freezing and thawing of water, which penetrates into the cracks, makes the rocks break up, so enlarging the depression. At the same time, the action of plucking takes place which stapens the sides. The depression is over-deepened by the movement of the glacier. The depression develops into the shape of an armchair with a distinctly concave floor. Some cirques contain glaciers, but in others the glaciers have melted and they now contain lakes called tarns.

Examples of cirques include those occupied by Hiddebn Tarn, Oblong Tarn, Gallery Tarn, Emerald Tarn etc, on Mt. Kenya, Lac du Speke on Mt. Ruwenzori and North Corrie in which lies Mawenzi Tarn on Mt. Kilimanjaro.

(c ) Arates. An arate is a steep-sided, knife-edge ridge separating two or three cirques. It is formed when their (cirques) walls are retreating backwards by the cutting back of the back walls of the cirques by plucking). In other words, there headward erosion of the halls of the cirques which is known as basal sapping as seen in the diagrams below.

Development of a pyramidal peak and erates.

(a)Three cirques containing glaciers - the arrows indicate the movements of the glaciers.

(b)The position after a prolonged period of erosion.

Pyramidal Peak.(Horn). This is a horn-shaped peak formed by the retreating walls of three or more cirques. The pyramidal peaks with their arêtes are characteristic features of glaciated highlands. Examples are point John, Midget peak, Point Lenana etc or Mt. Kenya and Albert and Alexandra peaks on Mount Ruwenzori.

Sometimes a sharp projection of a pinnacle may rise above an arête. These projections are called gendarmes. Example of this is the Tooth on Mount Kenya.

U-shaped valley (Glacial trough). This is a steep-sided, flat-bottomed, wide valley, which contains features formed both by glacial erosion and glacial deposition. Most U-shaped valleys were originally river valleys.

The valley is formed as a more powerful glacier with increased erosive power develops in a main river valley. This results in the glacier deepening, straightening and widening the valley through abrasion, freeze there and plucking. If there are interlocking spurs, they are planed off to form truncated spurs. This can be illustrated in the diagrams below.

Examples in East Africa are: Teleki, Hobley, Gorges, Mackinder etc in Mount Kenya and Mubuku and Bujuku on Mount Ruwenzori.

Hanging valley. This is a tributary valley of a U-shaped valley, which ends abruptly, high above the floor of the U-shaped and separated from it by an almost vertical slope. A small glacier with less erosive power occupying a tributary valley forms a Hanging valley. Vertical erosion of the main valley is greater than that of a tributary valley. When the main valley glacier melts, the tributary is left hanging.

If a river occupies the hanging valley, it plunges as a waterfall to the floor of the main valley, and sometimes it builds an alluvial fan. Below is a diagram for these features:

Fiord. If the sea, later occupies the lower end of a U-shaped valley, they are drowned and they form fiords. The sides of fiords are very steep. The diagram of fiord development can be seen

Crag and tail. This is a resistant mass of rock upstanding in the path of a moving ice (glacier). The glacier passes over this resistant mass of rock. Some glacier passes on either side of the upstanding rock. The side facing the oncoming ice is eroded and roughened by the ice. The side facing the oncoming ice is called Stoss. The downstream side is protected and some of the materials eroded at the stoss together with the moraines form a gentle sloping tail as seen in the diagram below:

Examples of crag and tail are found on Mt. Kilimanjaro where till deposited in the lee of some parasitic c.....forms crag and tail.

Roche Montonnee. This is an outcrop of resistant rock smoothed by ice on the upstream end into a gentle slope, and plucked on the downstream end to give a steep, jagged slope. It is the rock embedded in the base of the ice that smooth down the outcrop, sometimes cutting deep grooves on the surface of the outcrop. These grooves are called Striations. Roche Montonnee is a small feature, which looks like a small hill. It is found in both glaciated highlands and lowlands. The diagram is seen below:

Several roaches monotones are on the slopes of south of Mawanzi on Mount. Kilimanjaro. Examples exist along the Mobuku valley on Mount Ruwenzori and the Southern slopes of Mawanzi on Mount Kilimanjaro, near the snout of Lehana glacier up along Mt. Kenya.

D. GLACIER MOVEMENT AND DEPOSITION

A glacier moves because of the force of gravity and the pressure from the snowfield. When a glacier moves it erode the walls of the channel. The materials eroded by the glacier and other weathered materials are transported and deposited on low lands forming depositional features.

DEPOSITIONAL LANDFORMS

Terminal Moraine (end moraine)

Consists of boulder-clay deposited on the lowland by the melting glaciers. Sometimes ridges are formed by the spreading of Moraines. Technical Moraine marks the furthest point a glacier has moved:

Drumlins. These are elongated small hills found in glaciated lowlands. Drumlins are composed of boulder-clay, with their elongation in the direction of ice-flow. They range in height from a few metres to about 100 metres high and they may extend to about a kilometer or two kilometers in length. Sometimes they occur in great numbers and from high above they appear like eggs.

Eskers. These are long, winding ridges mainly composed of sand and gravel. The Moraine - forming eskers appear to be more sorted than the Moraine forming drumlins. They may vary in height from a few metres to about 70 metres and some of them may extend several kilometers in length.

Outwash plain. This is made from gravel and sand and developed outside of the terminal moraine by melt waters from the ice depositing sorted materials. Coarsen materials form the plain nearest to the terminal moraine, but the deposits get finer away from the moraine.

Erratic. Glaziers or ice-sheets sometimes deposit large boulders of varying sizes as they melt. Erratic blocks are composed of materials, which are different from the materials of the surrounding rocks.

Figure 9: A large boulder dropped by a glacier is called a glacial erratic.

(Source: http://en.wikipedia.org/wiki/File:Giebichenstein.jpg, License: CC-BY-SA)

Till plain. This is an extensive area of monotonous relief. The unsorted glacial deposit may burry the pre-existing valleys and hills to give an undulating relief or till plain. The till-plain landform appears featureless. Some of the till-plains, which are composed of mainly boulder-clay, may form fertile agricultural land.

Kettles. Form from detached ice blocks enclosed within the till after the retreat of the main ice sheet. Subsequent melting of an ice block leaves a depression which when filled with melt waters, forms a kettle lake.

Kames. These are small hills mainly composed of gravel and sand. The formation of these mounds may alternate with small depressions, which may be filled with melt water to form kettle lakes. Kames vary in shape and size. They occur in isolation or in groups. The diagram can be seen below:

Diagram showing the development of a Kame:

Most of these depositional features are not in East Africa except few. The reason is that, within the tropics the glaciers from Mount Kenya, Mount Kilimanjaro and Mount Ruwenzori melt before reaching the lands.

GLACIATED HIGHLANDS IN EAST AFRICA

Mount Kilimanjaro is in Tanzania near the boarder with Kenya. It is the highest mountain in Africa and rises to 5,895 metres above sea level. At the summit there is an ice-cap glacier, which fills the crater. The mountain has several other glaciers. On the lower slopes lateral moraines are common. Cirques are also found on this mountain. Among the most prominent terms is the Mawenzi Tarn. Besides there are outwash deposits and striated rock outcrops. There are two prominent peaks, namely Uhuru Peak and Kibo Peak.

Mount Kenya is the second highest mountain in Africa. It rises to 5,199 metres above sea level. The snowline is at approx.4,496 metres. Quite an extensive area of Mount Kenya is glaciated. Frost weathering has shattered the central peak of the volcano. At the summit of the Mountain are several corries (cirques) lying both arêtes sedges. Other prominent features are tarns and moraine-damned lakes. Prominent peaks are Batian, Lenana and Nelion are found important tarns include Teleki Tarn, Oblong Tarn and Hut Tarn.

The Ruwenzoris (block) are comprised of three main mountains, namely Mount Baker, Mount Stanley and Mount Speak. There are 37 glaciers on the Ruwenzoris. The highest peak is called Margarita and is on Mount Stanley. The snow line is at 4,750 metres. The glaciers on the Ruwenzoris are gradually getting smaller or retreating. The Ruwenzoris have several lakes such as Lake Bujuku and Lake Kitandara.

E. SIGNIFICANCE OF GLACIATION

Position significance:

The glaciers and ice caps provide melting water to the rivers during dry or hot periods e.g. the chagga receive salt water from Kilimanjaro in Tanzania. The Mobuku irrigation Scheme in Uganda is possible because of perennial snow and glaciers on the Ruwenzori.

The melt water can be used for both domestic and industrial purposes e.g. waters from river Nyamwamba originating from the Ruwenzoris is used in the cobalt factory in Kasese.

This water is also used for irrigation purposes e.g. Mobuku irrigation scheme uses water from Sebwe river from Mount Ruwenzori.

The glacial erosional and deposition features and the snow-capped peaks of Ruwenzoris, Mount Kenya and Kilimanjaro are beautiful sceneries, which attract tourists.

The waterfalls on hanging valleys are very potential for the generation of A.E.P. For example electricity is generated at Vivienne falls on the Gorges valley on Mt. Kenya, and that generated along river Mobuku on Mount Ruwenzori.

On regions where glaciations have occurred, boulder-clay and glacial till may be deposited. Such regions form fertile agricultural land.

The glaciers and ice caps lower temperatures making the adjacent areas cool and so prevent the existence of pests.

Glacial erosion and deposition are important processes in soil fertile, hence help to generate soils that can support arable agriculture e.g. soils have been ground from uplands and re-deposited with ground-up till in deep widened valleys such as in Teleki valley on Mt. Kenya.

The U-shaped valleys serve as sites for communication route ways. Good examples are found in Switzerland, where the railway systems are constructed along the U-shaped valleys of the Alps Mountains.

Negative significance:

- Glaciers act as an agent of erosion

- Glaciers Provide avalanches which are destructive to both man and crops

- Melt-water may cause flooding/floods

- Glaciated areas are unsuitable for cultivation because areas are bare.

- Glaciers and ice caps make the environment too cold for human habitation.

F. QUESTIONS FOR REVISION

1. Describe the processes leading to the formation of erosion at glacial features in East Africa.

Examine the landforms resulting from glacial erosion in the highland areas of East Africa.

2. Account for the development of erosional glacial landforms in East Africa.

4(a) Identify and describe the glacial features in the mountains of East

Africa.

(b) Of what importance are the mountains of East Africa to the people.

5. Examine the processes responsible for the formation of erosional glacial features on any one mountain in East Africa.

1. Examine the factors limiting glacial activity in East Africa.

Rock Resistance. Most rocks in East Africa are metamorphic and therefore tend to be most resistant to erosion by ice. Besides these rocks don't have many joints as is the case with sedimentary rocks. For these reasons glacial erosion is limited to abrasion only in most cases.

Altitude. Most of East Africa lies between 2,000 -3,000 metres above sea level. And for snow and ice to exist, a minimum of 4,500 metres above sea level should be attained. Only Mts. Kenya, Kilimanjaro and Ruwenzori attain these heights. These leaves the vast proportion of East Africa without snow and ice. Hence reasons for limited glacial activity.

Latitude . East Africa lies astride the equator. This means that maximum insulation is received throughout the year compared to other regions of the world. Yet for snow and ice to exist, temperatures of Zero and below should persist for some considerable time. This leaves the three mountains of Ruwenzori, Kenya and Kilimanjaro as the only of glacial activity.

Availability of rock debris. Much of East is located within the humid tropics. Therefore, chemical weathering processes are predominant and this limits the amount of debris available to cause abrasion. Besides, the three East African Mts. Have parent rocks that are fairly resistant except Kenya for its seasonally dissected, and yet Ruwenzori and Kilimanjaro are not well joints except for some faults along Ruwenzori. Hence the role of plucking is also limited.

Thickness and Depth of ice. The position of East Africa is such that it lies astride the equator. Hence perpetually high temperatures which limit large scale accumulation of snow and hence ice. Besides the three East African Mountains are not so high to induce significant reductions in temperatures that could lead to large-scale accumulation of snow. Consequently, little accumulation of snow and ice occur. Therefore the smaller the thickness and volume of a glacier the smaller its energy would be. Thus, this will have limited effect on molding the landscape.

The nature of relief. On the leeward side of the Ruwenzori there is limited snow covering hence limiting glacial activity.

The influence of global warming. Reducing the chances of large-scale accumulation of snow. Etc