These rock formations are known as stacks. Many stacks were once arches that have collapsed, leaving just the upright columns. Over time these will also topple into the waves. This is already apparent in the Taranaki region’s Three Sisters, pictured here. The most seaward of the stacks is the smallest and will most likely be the first to topple, leaving cartographers with the job of renaming the remaining stacks the Two Sisters.
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Photograph by Lloyd Homer
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