THE ISOSTATIC MOVEMENT

THE ISOSTATIC MOVEMENT

THE ISOSTATIC MOVEMENT
Isostatic movement: Is the movement materials either within or outside the earth crust.
Normally the earth is dynamic and is in motion all the time to keep or to find the balance
(equilibrium) where materials are moving in different ways in both vertical (upward and
downward) and horizontal (forward and backward). Normally materials are moving in
order to keep balance of the earth. The materials are usually moving because of
continuous processes operating either within the earth crust or on the earth surface.
TYPES OF ISOSTATIC MOVEMENT
i. Vertical movement/movement of weight
ii. Horizontal movement/heat accumulation

1. VERTICAL MOVEMENT/MOVEMENT OF WEIGHT
   Vertical moverment is also known as movement of weight. This refers to the upward
   and downward movement of materials which resulting in to isostatic adjustment. This
   movement is caused by the increase in weight of materials like ice accumulation which
   cause sinking of the crust (doward) and then if happen the ice melt the continent rising
   (upward). The movement is responsible for creating balance between the oceanic crust
   and the continental crust. Evidence of this movement is submergence of continental
   shelf of Antarctica which is covered to about 750m compared to 180m around the
   continents. The increase in weight is caused by melting of ice and deposits from the
   denudation.
2. HORIZONTAL MOVEMENT/HOT ACCUMULATION
   Horizontal movement/heat accumulation: This movement occurs when there is
   horizontal flow of mantle from the area of depressed to the area of uplifted to
   adjustment. Horizontal movement take place in the Somatic layer especially in the
   asthnosphere where there is continuous radioactive. The disintegration of rocks under
   the magma release heat which then accumulate and prevented by the more underlying
   solid rock hence this prices make the sima to move by finding balance.
   ANALOGY/EXAMPLES OF ISOSTACY THEORY
   Normally the isostacy theory may be made by the followings like:-
   i. Floated iceberg: Melting of ice make the decrease in weight of iceberg and cause to
   floats freely than non melted iceberg. The large iceberg sink much in to water.
   ii. Floated pieces of wood: The long piece of wood sink much down and rise much

above than the short piece of wood.
iii. Loaded and unloaded ship: The floating ships show how isostacy affect the
behaviour of crust as it float on the heavy mantle rock. The loaded ship sink much down
while the unloaded ship rising up.
EVIDENCES PROVING THE EXISTENCE OF ISOSTATIC MOVEMENT
Qn: The earth is restless. Discuss this statement by giving seven (7) points.

1. Formation of depressions on the earth crust: The isostatic movement has lead to the
   formation of depression on the earth surface in different parts of the world like in the
   northern part of America and Europe was due to the weight of ice sheets of vast
   thickness during the ice age.
2. Rising of the earth crust: After the melting ice sheets, the crust has been rising
   slowly for example, there are numerous former beaches that occur around the coast of
   Scandinavia. They now lie between 8m-30m above the present day beaches. These old
   beaches have been raised because of the uplift of the land.
3. Sinking of continental shelf: The continental shelf around Antarctica is covered with
   sea water to a depth of about 750m compared with 180m around other continents.
   However the sinking of continental shelf has led to the formation of submerged coasts
   like Rias and Estuaries between the coast lands of Gambia and Sierra Leone. Another
   indicator of sinking of continental shelf is the submergence of forests on the shores of
   Britain as a result of increase in sea level.
4. Presence of raised beaches in scandnavia: The raised beach in Scandinavia is
   covered by mass of ice sheet about 10000 years ago. This lie between 8-30cm above
   the present beaches. However this situation has caused by melting of ice.
5. Presence of land uplift in Canada: Normally in eastern Canada and southern Ontario
   there is raised land much as 100m during the last 6000 years ago. However the land
   risen during the ice age where raised the way ice sheet melted.
6. Existence of mountain ranges: Despite of continuous denudation through erosion
   and mass wasting but mountains have maintained their ranges or heights. Example
   mount Kilimanjaro has maintained its height of about 5895m for thousand years.
7. Existence of water bodies and depression areas: Despite of continuous deposition
   of deposits in to water bodies but ocean and lakes like Indian ocean, Antarctic ocean,
   lake Victoria, lake Nyasa and Tanganyika have not disappeared.
   EFFECTS OF DISTURBANCE OF ISOSTATIC EQUILIBRIUM

1. It can led to occurance of the Earth quakes: Earth movements (gradual)
2. It can led to the occurance Subsidence and uplift (submerged coast /raised beaches).
3. It contributes to faulting of lithosphere which resulted in to formation of rift valleys or
   block mountains, lift blocks.
4. It can led to the formation of folds and Fold Mountains.
5. It can led to Volcanic eruptions and its associated features.
6. It can led to displacement of lithosphere leading to plate tectonic movement.
   IMPORTANCE OF THE THEORY
   Qn: Refute the statement that “The Isostacy theory is irrelevant to Tanzanian
   societies” Give six points.
7. It provides the knowledge on the dynamic state of the earth‟s crust that is the earth‟s
   crust is not static but it is always dynamic as it tends to balance itself after some
   disturbances with the influence of the gravitational force.2. The analogy that the crust
   floats on the mantle, just like the iceberg floats on and the ocean or sea water, is so
   crucial in the understanding of the theories of plate tectonics and continental drift.
8. The theory also helps in understanding how different landforms were formed.
9. It also gives the basic for predicting the future of the crustal state at any particular
   place on the earth‟s surface.
10. It can also help human being in taking some precautions depending on the nature of
    the phenomena that might have been observed in the course of time, like the
    occurrence of ice sheets and melting of ice.
11. It provide knowledge on studying the seismic waves and the occurrence of
    earthquake.
12. It helps geographers to understand the distribution of earth quakes.