Given the task definition and input, reply with output. In this task you will be given a text passage from a trivia quiz. You should choose the category this question belongs to from these categories: History, Science, Social Science, Fine Arts, Literature. You can only choose one category, so if in doubt, please choose the closest match.

The break-off events of these objects are exemplified by an event affecting Altels in 1895, which was thought to have been triggered by infiltrated water. A tunnel under one of these objects in Kluane National Park collapsed and formed a canyon 20 years after a surge that almost recreated a lake. The islands Santonen and Hanhinen merged into Hailuoto, a process called rebound, after one of these objects receded. They are divided into zones of ablation and accumulation, and they leave behind moraines at their furthest extent. Sometimes forming aretes between their 'u'-shaped valleys, for 10 points, name these moving sheets of ice which cover Greenland and Antarctica.
Science