Question
Analyze critically the theory of mountain-building as proposed by Holmes. ( UPPSC 1992)
Answer.
Arthur Holmes gave the theory of thermal convection currents in 1928. The main objective of the theory was to find an explanation for the formation of continents and oceans. However, Holmes' theory of thermal convection current also explains mountain formation.
According to Arthur Holmes:
- The origin and functioning of the convection current depend on the presence of radioactive elements in the rocks.
- Due to the greater thickness of the crust at the equator, thermal convection currents rise near the equator and flow down near the poles because the depth of the crust at the poles is shallow.
- Divergent convective currents form seas and oceans as crustal blocks move away.
- Mountains form in the convergence zone of convection currents as they bring the crust blocks together.
- There are three stages in the formation of fold mountains. In the initial phase, the convection current creates a geosyncline region in the area of convergence.
- The second stage is also called the orogenesis stage. This leads to an increase in the velocity of the convection currents and is accompanied by a shorter duration of this phase. In this phase, there is an upward movement in the geo-syncline regions.
- The third stage is the final stage of mountain formation in which the rising material cools and solidifies and forms the mountain range.
Evaluation of Arthur Holmes' mountain-building theory:
- The entire process of mountain formation is dependent on a convection current led by radioactive elements, but there is a lack of scientific evidence about the radioactive elements that provide the driving force of the convective current.
- This theory is able to explain only fold mountains, not block mountains.
- The theory is also not able to correctly explain the volcanic mountain because some volcanic mountains are not found in the convergence or divergence zone of the convective current.
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