How can a sea arch eventually become a sea stack?

A sea arch is a coastal landform created by the differential erosion of bedrock along a rocky coast. As waves continuously attack the cliff face, they carve out openings that form these archways.1

The transition from a sea arch to a sea stack occurs through the process of continued erosion. As the erosional forces persist, the structural integrity of the arch is eventually compromised, leading to the collapse of the arch's span. This collapse leaves behind an isolated, vertical column of rock known as a sea stack standing upon the wave-cut platform. Over time, ongoing wave action will continue to erode the stack until it is completely worn away, leaving no trace of the feature.12