firnification

Firnification is the process by which snow transforms into firn, and subsequently into glacial ice. This occurs over extended periods as snow is buried under accumulating layers of new snowfall. The weight of the overlying snow compacts the older snow, causing the individual snow crystals to recrystallize. Initially, the snow loses its fluffy structure and becomes denser, with smaller air pockets. As this process continues, the air pockets become even smaller and more rounded, and the density increases significantly.

The transformation from fresh snow to firn is characterized by a decrease in porosity and an increase in density. Fresh snow typically has a density of less than 0.5 grams per cubic centimeter, while firn can have a density ranging from 0.5 to 0.8 grams per cubic centimeter. The transition from firn to glacial ice occurs when the density reaches approximately 0.83 grams per cubic centimeter, at which point most of the air has been squeezed out, and the firn has become a solid, crystalline mass of ice.

Firnification is a crucial part of glacier formation and the accumulation of ice sheets. It is a gradual process that can take decades to centuries, depending on the climate and the rate of snow accumulation. The specific conditions of temperature, pressure, and time all play a role in how quickly snow firnifies and eventually turns into glacial ice. This transformation is essential for understanding ice dynamics, paleoclimate records preserved in ice cores, and the long-term behavior of glaciers and ice sheets.