Glacial ice is formed through a metamorphic process of snow becoming ice. Glacier begins to form when snow remains in the same place all year round. As the years go by, snow accumulate to transform into ice.
Each year, new layers are formed, these new layers compress the previous layers. Over the years, the compression is transformed into large thickened glacial ice.
Firn is formed in the process, firm takes about a year to form. The firn is later changed into solid glacial ice. The simply interpretation of how glacial ice is formed is shown below.
Snow flakes ------> Firn -----> Glacial ice.
The dash lines represent the metamorphic processes that occur in the formation of glacial ice.
