A stack or seastack is a geological landform consisting of a steep and often vertical column or columns of rock in the sea near a coast, formed by erosion.Stacks are formed over time by wind and water, processes of coastal geomorphology.They are formed when part of a headland is eroded by hydraulic action, which is the force of the sea or water crashing against the rock. The force of the water weakens cracks in the headland, causing them to later collapse, forming free-standing stacks and even a small island. Without the constant presence of water, stacks also form when a natural arch collapses under gravity, due to sub-aerial processes like wind erosion. Stacks can provide important nesting locations for seabirds, and many are popular for rock climbing.
Stacks at the island of Fårö, southern Sweden
Isolated steep-sided, rocky oceanic islets, typically of volcanic origin, are also loosely called “stacks” or “volcanic stacks”.
Mount Taranaki, or Mount Egmont, is an activebut quiescent stratovolcano in the Taranaki region on the west coast of New Zealand’s North Island. Although the mountain is more commonly referred to as Taranaki, it has two official names under the alternative names policy of the New Zealand Geographic Board.The 2518-metre-high mountain is one of the most symmetrical volcanic cones in the world. There is a secondary cone, Fanthams Peak (M?ori: Panitahi), 1,966 metres (6,450 ft), on the south side.Because of its resemblance to Mount Fuji, Taranaki provided the backdrop for the movie The Last Samurai.