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S.3 Geography Notes

Formation of the Ice (Glaciers)


Glaciers are formed when the temperatures of the air fall below freezing point (0°c) which makes water vapour to condense and form snow in the valley.  

When the snow accumulates for a long time in successive layers there is increasing pressure on the overlying layers that compresses and hardens the snow into ice. Permanent snow fields or neve are formed when the rate of snow accumulation is greater than the rate of ice melting and flowing down slope following the existing river valleys. 


In East Africa glacial activities are limited to only three areas like Mountains Kilimanjaro, Kenya, and Rwenzori. These areas have conditions suitable for glacial formation, for instance.

1.  Presence pf high altitude of above 4500m above sea level with very cold temperatures which encourages freezing 

2.  The existence of very cold temperatures of below 0º allows water freezing to form snow.

3.  Presence of several hollows/depressions that collect and accumulate water/snow thereby turning into ice.

4.  Existence of high humidity in the atmosphere that condenses leading to precipitation

5.  Existence of gentle sloping relief accelerates glacial movement by gravity.  


The effect of ice on the landscape is important both directly and indirectly. Directly ice is a major agent of erosion, transportation and deposition and indirectly ice affects landscapes through the melt waters that issue from the ice front. All materials transported and deposited by ice are called till (moraine). This includes materials carried on, within and beneath the ice and they range from very small particles to huge boulders like sand, clay, gravel, rocks and boulders. 

i)  Glacial erosion, which predominates in the highlands, consists of three processes:  

Plucking is a quarrying process by which parts of the underlying rocks are frozen into the base of the ice and pulled away. It is more effective on well-jointed rocks where melt water can free into the cracks. The cracks are then widened and deepened due to increase in the volume hence breaking of the rock.  

Glacial abrasion is the grinding process in which stones and boulders frozen into the moving ice are dragged over the underlying rocks thereby polishing and scratching the surface.  

Sapping is the break-up of rocks by alternate freezing and thawing of water at the bottom of cracks between a mass of ice and the side and floor of the valley or the side of the rock of the mountain.  Erosion of the valley glaciers depends on the following factors:

  • Resistance of the rock  
  • Speeds of the glacier - fast glaciers have a great effect compared to slow glaciers.
  • Hard rocks will resist erosion while weak rock will be eroded.
  • The thickness and weight of the glacier (ice) will determine the rate of erosion. It will increase the pressure.
  • Availability of rock debris as erosion tool which a binding effect as it moves.


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