It is formed from snow after passing through one summer melt season and becomes glacier ice after its permeability to liquid water falls to zero (Source: Carbon Dioxide Information Analysis Center, 1990).
(It; is formed; from snow; T:after passing through one summer melt season) (It; after passing; through one summer melt season) (It; becomes; glacier ice after its permeability to liquid water)
It It It
is formed after passing becomes
from snow T:after passing through one summer melt season
through one summer melt season
glacier ice after its permeability to liquid water