The correct option is 2 and 3 only.
Explanation
Pediments are gently inclined rocky floors found at the foot of mountains. They are characteristic erosional landforms associated with the evolution of landscapes in arid and semi-arid environments. They are formed through the erosion of the mountain front via a combination of lateral erosion by streams and sheet flooding.
Statement-wise Analysis
- Statement 1 is Incorrect.
Pediments are not formed in humid regions. They are typical of arid and semi-arid climates. In humid regions, the dominant erosional plain is typically a peneplain, formed by down-wasting and rounding of relief. Pediments are associated with pediplains.
- Statement 2 is Correct.
This statement describes the typical slope profile associated with pediments. A pediment is located at the base of a mountain front. The profile generally consists of the pediment (gentle slope) at the bottom, surmounted by a steep wash slope (debris slope), which is in turn topped by a vertical or steep cliff (free face). Thus, pediments are characteristically found below a steep wash slope and a free face.
- Statement 3 is Correct.
Pediments evolve through the process of parallel retreat of slopes (also known as back-wasting). As the steep mountain front (cliff and debris slope) erodes and retreats backward, the pediment extends outward to replace the retreating mountain. Therefore, they extend backwards at the expense of the mountain front.
Key Takeaway
Pediments are arid erosional plains formed by the backward retreat of mountain fronts (scarp retreat), whereas Peneplains are humid erosional plains formed by the down-wearing of relief.