Park Pass: a glacier in retreat, showing a lake of melted ice at its foot. Park Pass glacier is one of the 50 index glaciers that have been monitored since 1977. The glacier flows down the southwest face of Poseidon Peak at the head of the Rock Burn, which flows into Dart River (which flows into Lake Wakatipu). It is within Mt Aspiring National Park. Since the survey started we have observed the development and growth of a small terminal lake and in recent years this lake has had large icebergs in it that have calved off the main glacier tongue. Like many of the larger glaciers (e.g., the Tasman, Murchison and Mueller glaciers at Mt Cook), this glacier has shown dramatic retreat and ice loss following years of negative mass balance and lake development.