The correct option is 1 and 3 only.
Explanation
Geomorphic processes are classified into endogenic (internal) and exogenic (external) forces. Diastrophism is an endogenic process that moves, elevates, or builds up portions of the earth’s crust. It primarily includes two distinct processes: Orogeny and Epeirogeny.
Statement-wise Analysis:
- Statement 1 is Correct: Orogeny (from the Greek oros meaning mountain) is a mountain-building process. It is caused by horizontal (tangential) forces affecting long and narrow belts of the earth’s crust. This process involves intense folding, thrusting, and severe structural deformation, leading to the formation of fold mountains (e.g., the Himalayas).
- Statement 2 is Incorrect: Epeirogeny (from the Greek epeiros meaning land/continent) is a continental-building process. It involves vertical (radial) forces causing uplift or subsidence of large continental masses. It results in the formation of plateaus, basins, or broad continental shelves, rather than mountains.
- Statement 3 is Correct: Both orogeny and epeirogeny are diastrophic forces that subject the earth's crust to stress. While orogeny involves severe folding and faulting due to compression, epeirogenic movements (uplift or warping) can also generate tension or compression, leading to faulting and fracturing of the crust.
Key Takeaway:
Orogeny is driven by horizontal forces and results in mountain building (folding), whereas Epeirogeny is driven by vertical forces and results in continental building (uplift or subsidence).