The correct option is 1 and 3 only.
Explanation
A Peneplain (derived from Latin paene meaning "almost" and plain) represents the theoretical end-product of the fluvial cycle of erosion. The concept was popularized by the geomorphologist W.M. Davis to describe a landscape that has been worn down by rivers and weathering to a low-relief plain near the base level.
Statement-wise Analysis:
- Statement 1 is Correct: A peneplain is a type of erosional plain formed specifically as a result of prolonged stream erosion (fluvial action) and weathering. It signifies the degradation of a landmass over a vast period.
- Statement 2 is Incorrect: A peneplain is characterized by low relief with gentle, undulating slopes, not high relief. Furthermore, it is not completely devoid of features; it typically contains scattered, resistant rock remnants that have withstood erosion. These isolated residual hills are technically known as Monadnocks.
- Statement 3 is Correct: The formation of a peneplain is the defining feature of the old stage (senile stage) of a river's life cycle. In this stage, vertical erosion ceases, lateral erosion dominates, and the drainage divides are lowered to form a featureless plain.
Key Takeaway:
A Peneplain is a low-relief erosional plain formed in the old stage of the fluvial cycle, characterized by gentle undulations and residual hills called Monadnocks.