SUB TOPIC 2
INLAND DRAINAGE
LAKES
A
lake is a body of water which occupies a basin, depression or hollow on the
surface of the earth. Some of the lakes are temporal while others are
permanent. The size, depth and
permanence of lakes depend on the nature of the basin and availability of water
(water source).
Many
lakes contain fresh water and thus are referred to as fresh water lake. However some do contain salty water. Reasons
for saltiness of lake water include the following:
1. Absence
of some lakes outlet in form of rivers which would drain away some of the salts
contained in them. This leads to the accumulation of salts in the water.
2. In
areas which are hot and dry, the rate of evaporation is very high. Due to
excessive evaporation it results into concentration and accumulation of the
dissolved mineral salts in the lake.
3. Some
lakes do not have enough fresh water rivers emptying into them.
4. Nature
of underlying rock over which the lake water is in contact with influence
salinity of the lake water.
FORMATION AND CLASSIFICATION OF LAKES:
Lake
classification is based on some of the criteria includes, Earth movement, Vulcanicity, erosion, Deposition, Human
activities, mass movement, falling meteorites and vegetation influence.
a) LAKES DUE TO EARTH’S
MOVEMENT: Earths movement caused by forces
originating from the interior of the earth.
Such forces results into the formation of faulting lakes and depression
Lakes.
Faulting lakes/rift
valley lakes:
a rift valley lakes are the lakes formed due to sinking of land between
two parallel faults. The lakes formed are deep, narrow and elongated in
character. Water collects within these formed depressions to form lakes.
Example of such lakes includes Lake Tanganyika, Lake Nyasa (Malawi), Lake
Rudolf, Edward and Albert.
Down warping lakes: are the Lakes formed due to the warping,
sagging, bending and fracturing of the earth’s crust which results into
formation of depression. Once such depression occur it results into formation
of Lakes when water collects on them. Example includes Lake Victoria, Lake
Titicaca, Lake Superior and Caspian Sea.
b)
LAKE
FORMED BY GLACIATION:
Cirque or Tarn Lakes:
they are the lakes formed when water occupies armed-chair shaped depression on
the side of mountain called cirque. Example of tarn lakes includes teleki tarn,
Red Tarn Lake in England.
Kettle lakes:
these are depressions in the outwash plain left by the melting of masses of
stagnant ice. They are irregular because of uneven moraine.
Ribbon /trough lake:
they are the lakes which are formed when water occupy a depression in a
U-shaped valley. Such lakes are narrow and elongated in shape .they are also
called finger lakes. Example is Lake Ullswater.
Rock hollow lakes: they
are formed when water occupy the depression left by rock due to glacial erosion
through process of ice scouring. Such lakes are common in Finland
Moraine dammed lake:
are the lakes formed due to glacial deposition where by glacial deposits
moraine across a river valley where over time it blocks the flow of river and
water collects to form a Lake.(moraine dammed lake)example lake Windermere of the lake district.
c)
LAKES
DUE TO VOLCANIC ACTIVITIES:
Crater and Caldera Lakes:
are the lakes formed when water occupies depression formed at the summit of the
volcanic mountain. The depression is the outcome of volcanic explosion. When
water occupies a small depression it is called Crater Lake while when water
occupy large depression on the summit it is called Caldera Lake. Example of
crater lakes includes Lake Chala, lake sonanchi and lake paradise on mount
marsabit.
Lava –dammed lakes:
they are the lakes formed where lava cuts and solidifies across a river valley
to block the flow of water. Thus water accumulates behind the solidified mass
of lava and form a lake. Such lakes are elongated in shape as the occupy a
river valley. Example of such lakes
includes Galilee Sea formed from blocking of Jordan River valley,
d) SOLUTION LAKES:
Karst/solution:
are the lakes formed where water /rain water occupy the depression in a karst
region formed due to formation of depression by chemical weathering
(carbonation) process in limestone areas. Such lakes are also called karst
lakes. Example Lake Scutari in Yugoslavia, Lake Guinas and Lake Ojikoto in
Namibia.
e) WIND EROSION LAKES:
Wind deflated lakes:
are lakes formed where wind deflation erode and result into formation of
depression in desert. If such depressions are small and shallow pan lakes may
form. But sometimes such depression goes deeper to expose water table and
result into formation of Oasis lakes like in Qattara Depression in Egypt.
f) DEPOSITION LAKES:
River deposition lakes
(ox bow lakes): are lakes formed where combining
process of erosion on one side of meander and deposition on the other side of
the mountain results into leaving behind horse shoe like depression filled with
water called ox-bow Lake. Eg. Shikababu, gambi and mkunguya in river Tana.
Marine deposited lakes:
they are also called lagoon lakes. They are lakes formed due to accumulation
polyps or sands and other materials parallel but within the water near the
coast. Water occupies a gap between the shore and the sea and form a lagoon.
Example lake Sare, Lake Nagugabo in SW of Lake Victoria, also lake Nokoye in
Benin, Ebrie in Ivory Coast.
Lakes due to massmovent: they are also called barrier lakes. They are
formed when mass wasting deposits materials across the river valley to cause
water to accumulate. Example Lake Gormire in Yorkshire, ffynnon French.
g)
MAN
MADE LAKES:
Human
made lakes includes number of lakes made by human being for different purposes.
Example includes dams such as Mtera and Kidatu dams in Tanzania. Also lakes
made for recreational activities such as lake gardens, Kuala Lumpur and Taiping
lakes.
Also
mining activities lives behind pits where once water collects into them lakes
are formed.
h)
BIOLOGICAL
LAKES:
Lakes made by animals:
animals such as beaver’s collects logs and other tree branches across a river
valley to block flow of river hence water collects and form a lake called
beaver lakes or animal lake. Example beaver
lake in Yellowstone National park
U.S.A.
i) METEORITES LAKES:
they are formed due to falling of meteorites which results into formation of
depression. Once such depression are filled with water are called meteorites
lakes. Example Lake Bosumtwi in Ghana.
- GROUND WATER || WATER MASSES || FORMATION AND CLASSIFICATION OF LAKES: PART THREE
- GROUND WATER || WATER MASSES || SIGNIFICANCE OF LAKES. PART FOUR
- GROUND WATER || WATER MASSES || IMPORTANCE OF WETLANDS PART FIVE
- GROUND WATER || WATER MASSES || CORAL COASTS PART SIX
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