Here's how it happens:

1. Wave action: The relentless pounding of waves against the coastline is the primary force behind sea stack formation. Waves erode the softer rock along the shore, creating caves and arches.

2. Hydraulic action: The force of water entering and exiting these caves creates pressure that weakens the rock structure.

3. Abrasion: The waves carry sand and pebbles that grind against the rock, further eroding it.

4. Weathering: Rain, wind, and frost can further break down the rock.

Over time, the arches eventually collapse, leaving behind isolated columns of rock called sea stacks.

Deposition is the process of adding sediment to a landform. While deposition plays a role in shaping coastlines, it's not directly responsible for creating sea stacks. Deposition might create features like beaches or sandbars, but it doesn't carve out the dramatic structures we see in sea stacks.