Sea stack
Also called: Stack · Topic: Landforms and their Evolution: Rivers, Groundwater, Glaciers, Waves and Wind · NCERT: Class 9, Ch 2 "Shaping of the Earth's Surface"; Class 11, Ch 6 "Landforms and their Evolution"
Meaning
A sea stack is a pillar of hard rock standing on its own in the sea, close to the shore. It forms in steps. Waves hollow out sea caves on both sides of a headland, which is a piece of land sticking out into the sea. The caves meet and make a sea arch. Later the roof of the arch falls in, and the outer part is left standing as a stack. Waves keep attacking the stack too, so it is temporary and will finally fall.
Example
The Twelve Apostles off the coast of Victoria, Australia, are tall limestone stacks. They are what is left of cliffs that waves have cut back. Some of them have already fallen.
Don't confuse with
- Sea arch: an arch still has a rock roof over open water. A stack is left only after that roof falls. Example of an arch: Neil Island (Shaheed Dweep), Andamans.
- Inselberg: this is also a leftover hill, but it stands on a dry plain and was shaped by desert processes, not by waves.
Related concepts
- Emergent coast
- Submergent coast
- Ria coast
- Longshore current
- Coastal erosion
- Sea cliff
- Wave-cut platform
- Sea cave
- Sea arch