How a glacier is formed

1) Snow falls and avalanches deposit on the glacier. Low density due to air spaces.

2) Neve/Firn is produced after repeated freezing and thawing the compaction converting the snow into opaque ice.

3) Further compression and recrystallisation converts the neve/firn into glacial ice (very dense). This ice has a bluish colour. The process takes between 25 years (e.g Switzerland) and 200 years (e.g Greenland).