The correct option is 1 and 3 only.
Explanation
Potholes and plunge pools are distinct landforms associated with the erosional work of running water (rivers). These features are typically observed in the upper or youthful stage of a river's course, where the gradient is steep, and vertical erosion is the dominant process.
Statement-wise Analysis:
- Statement 1 is Correct: Potholes are more or less circular depressions formed over the rocky beds of hill-streams. They are created when stream water forms swirling eddies, causing stones, pebbles, and boulders to rotate and drill into the bedrock. This mechanical drilling process is known as abrasion.
- Statement 2 is Incorrect: Plunge pools are erosional features, not depositional ones, and they are not found in deltas. A plunge pool is a large, deep depression formed at the foot of a waterfall. It is created by the sheer force of falling water (hydraulic action) and the abrasion caused by rock fragments swirling at the base. Deltas are depositional landforms found at the mouth of a river.
- Statement 3 is Correct: Both potholes and plunge pools are formed primarily by the process of erosion. Potholes are formed by the abrasive action of sediments caught in water eddies, while plunge pools are formed by the accelerated erosion at the base of a waterfall due to the impact of falling water.
Key Takeaway:
Potholes and plunge pools are erosional landforms characteristic of a river's youthful stage. They are formed through mechanical wear (abrasion and hydraulic action) and are distinct from depositional features such as alluvial fans or deltas.