The correct option is 1 and 2 only.
Explanation
Potholes are cylindrical or circular depressions formed in the rocky beds of river valleys. They are characteristic erosional landforms produced by running water (fluvial action), typically observed in the upper course or youthful stage of a river where the gradient is steep and the bed is rocky.
Statement-wise Analysis
- Statement 1 is Correct: Potholes are formed over the rocky beds of hill-streams. In these areas, the riverbed consists of hard rock, and the water flow is turbulent, creating conditions necessary for the drilling action that forms these depressions.
- Statement 2 is Correct: The formation of potholes is primarily driven by stream erosion aided by abrasion. Eddies (swirling currents) in the flowing water catch sediments like pebbles, stones, and boulders. These sediments are rotated within small natural depressions, grinding and drilling into the bedrock, thereby enlarging the depressions into potholes.
- Statement 3 is Incorrect: According to geomorphological principles, when small potholes enlarge and eventually merge or join, the result is the deepening of the stream valley. Plunge pools are distinct features; they are large, deep potholes formed specifically at the base of waterfalls due to the sheer impact of falling water and the rotation of boulders. Potholes joining together do not form plunge pools; rather, plunge pools are a specific type of depression associated with waterfalls.
Key Takeaway
Potholes are circular depressions on rocky riverbeds caused by abrasion from swirling sediments. Their merging leads to valley deepening, whereas plunge pools are deep depressions formed exclusively at the foot of waterfalls.