Geography Answer Writing Practice 2018 - Week 1 - Question 1
90 Days Geography Answer Writing Practice Question 1 for 12-Nov-2018
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12-Nov-2018 - Question 1
Evaluate how far Kober's geosynclinal theory explains the mountain building process. 300 words (2018)
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Kober attempted to explain the theory of origin of mountains based on his geosynclinal theory.
He considered long and wide mobile zones of water in places of present-day mountains called geosynclines or orogen which were surrounded by rigid masses called kratogen (forelands) e.g. Canadian shield, peninsular India etc. Mountains are formed out of these geosynclines.
He proposed three stages of mountain building:
The first stage is related to the creation of geosynclines due to the force of contraction caused by the cooling of the earth. Erosional material from the kratogen is deposited in the geosyncline causing sedimentation and subsidence.
In this stage, the kratogen start to move towards one another due to horizontal movements caused by force of contraction. The compressive force thus generated, causes contraction, squeezing and ultimately folding of the geosynclinal sediments to form mountain ranges. The parallel ranges formed on either side are termed as randketten.
The third stage is characterised by a gradual rise of mountains and their denudation by fluvial and other processes. Continuous denudation results in a gradual lowering of the height of mountains.
The theory can be evaluated as follows:
It accounts of various aspects of mountain building as in this theory, folding depends upon the intensity of compressive forces. If the forces are of moderate intensity and normal, only the marginal sediments are folded into randketten while the middle segments are unaffected and lead to the formation of median mass e.g. Tibetan plateau between the Kunlun Mountains and the Himalayas.
After the advent of plate tectonic theory, the concept of Kober that both forelands move together has been validated as in seen from palaeo-magnetic evidence and seafloor spreading.
And its limitations are as follows:
The force of contraction generated due to cooling of the earth as envisaged by Kober is not sufficient to cause mountain building.
Though it explains the east-west extending mountains like the Alps and the Himalayas, it does not explain the north-south extending mountains like the Rockies and the Andes.
Thus, though it had its limitations as seen above, Kober’s theory is given credit for advancing the idea of the formation of mountains from geosynclines.