The coastal columnar formations (stacks) northwest of Kaspakas on the beach of Agios Ioannis are geoforms formed by the sea eroding pyroclastic formations caused by intense volcanic activity during the Lower Miocene.

Coastal columns formations (stacks) refer to rock formations that rise above sea level along rocky beaches. They occur as a result of the strong differential erosion of a rocky beach by the sea waves and wind.

The definition “stack” is derived from the word “stakkur” which is the Scandinavian dialect of the Faeroe Islands, where these coastal formations are common along the high, steep, and rocky beaches.