Previous Year Question
Given below are two statements, one is labelled as Assertion (A) and the other as Reason (R).
Assertion (A): The Himalayas are still rising.
Reason (R): The Indian tectonic plate is colliding with the Eurasian plate.
Select the correct answer from the codes given below:
Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(A) is false, but (R) is true.
Both (A) and (R) are true and (R) is the correct explanation of (A).
(A) is true, but (R) is false.
Correct Answer: C
Detailed Solution
The Himalayas were formed by the continental collision of the Indian Plate and the Eurasian Plate. The major phase of collision began approximately 40–50 million years ago as the Indian landmass moved northward and collided with Eurasia. Since the crust of both continental plates is relatively buoyant, one entire plate could not easily be subducted into the mantle; instead, compression, folding, faulting and uplift of the crust produced the Himalayan mountain system.
This tectonic convergence has not ended. Modern measurements indicate that the Indian and Eurasian plates show a relative convergence of approximately 40–50 mm per year across the Himalayan region. This continuing convergence produces ongoing crustal shortening and deformation.
Because of this active tectonic process, the Himalayas are a geologically young and tectonically active mountain system. The actual uplift rate is not uniform throughout the region because erosion, fault movement and local tectonic processes operate simultaneously. Nevertheless, in the broader geological sense, uplift of the Himalayas continues.
The same ongoing collision is also a major cause of the high seismicity of the Himalayan region. Plate movement causes strain to accumulate along faults and thrust zones, and earthquakes can occur when this accumulated strain is released.
Therefore, the continuing collision/convergence of the Indian Plate with the Eurasian Plate is the fundamental cause of the ongoing uplift of the Himalayas, so Reason (R) correctly explains Assertion (A).