New Zealand contains approximately 2900 glaciers over 1 hectare (2.5 acres) in size, almost all of them along the Southern Alps, the main divide of the South Island. This is down from around 3100 glaciers recorded in the late 1970s, due to ongoing changes to the earth's climate. Roughly one-sixth of New Zealand's glaciers are over 10 hectares (25 acres) in size, with the largest – Tasman Glacier – with an area of 101 square kilometres (39 sq mi). Eight of New Zealand's glaciers are found on Mount Ruapehu, and represent the only glaciers within mainland New Zealand outside of the South Island.