The time it takes for glacier ice to form depends on the temperature around its general location. Glacial ice starts out as snowflakes that remain in a particular area and gets packed with more snow in the succeeding years. In time, the packed snowflakes becomes firn, and firn eventually becomes glacial ice.
When snowfall accumulates in a particular area, the weight of the snowfall in the winters following compresses it to form into larger grains. This packed ice is known as firn and it can form in as little time as two years or it may take 100 years in colder parts of the world. When the grains in the firn become more compressed, the areas between the grains are sealed off, thus forming a large lump of glacial ice crystal. When ice flows appear in a snow patch, it is a sign that a glacier has formed.