Temperature low enough to retain snow year round (high latitude and altitude. Sufficient snow: some polar climates are very dry, so glaciers do not develop. The ice line where glaciers can form is at seal level at the poles and head towards at the equator. You would like to take a piece of the core of the ice because it gives you a good idea of what happened in the hydrological era. Often there is bubbles of original atmosphere that gets trapped in the bubbles and its good way to record. You have enough height where snow doesn"t melt in the summer. In ontario it was formed by continental glacier. There is one in antarctica and one in greenland. Snow lands in center and things squish out moving in all directions. They move out in all directions from a very high center, squishing out like pancake batter.