The correct option is 1, 2 and 3.
Explanation
Sea stacks are distinct coastal landforms resulting from the erosive action of waves on headlands. They represent a specific stage in the sequence of marine erosion, evolving from caves and arches into isolated pillars of rock.
Statement-wise Analysis:
- Statement 1 is Correct: Sea stacks are temporary erosional features. They are formed by the continuous wave attack on coastal rocks. Being subject to constant erosion at their base, they are geologically transient and eventually collapse.
- Statement 2 is Correct: Sea stacks are composed of resistant masses of rock. They are remnants of a headland or cliff that have been isolated from the mainland. The process typically involves the formation of caves on opposite sides of a headland, which merge to form an arch; when the roof of the arch collapses, the isolated pillar remaining is the stack.
- Statement 3 is Correct: As the cycle of erosion continues, sea stacks are worn down into shorter features known as stumps and eventually disappear. The continuous retreat of cliffs and the leveling of the wave-cut platform can, over long periods, lead to the formation of narrow coastal plains as the coastline smooths out.
Key Takeaway:
The evolutionary sequence of coastal erosion on a headland is: Cave → Arch → Stack → Stump. All these features are temporary and indicative of an active erosional coastline.