In the Andes, glaciers only form above the snowline, where snow persists throughout the year. Their formation depends on latitude, altitude, and annual precipitation. As snow accumulates it compresses the underlying snow, creating a layer of dense snow, called a firn. As the snow continues to accumulate the pressure increases, further compacting the firn, which develops into solid glacier ice. When this ice gets thick enough the glacier begins
to flow, due to the force of its own mass under gravity, either by sliding or internal deformation.
From collection: The Andean Glacier and Water Atlas