Firn
Definition and Formation
Firn is a type of old snow that has been compacted and recrystallized, forming a dense, icy material. It is an intermediate stage between snow and glacier ice, often found in high mountain regions and polar environments. The term "firn" originates from the Swiss German word for "last year's", reflecting its age and transformation from fresh snow.
Firn forms through a process known as firnification, which involves the metamorphism of snow under the influence of temperature and pressure. This process begins when fresh snow falls and is subjected to various weather conditions. Over time, the snow undergoes compaction and recrystallization, gradually transforming into firn.
Characteristics
Firn is characterized by its granular, sugar-like texture and its higher density compared to fresh snow. It typically has a density of 400-830 kg/m³, compared to the density of fresh snow which is usually around 100 kg/m³. The increase in density is a result of the compaction and recrystallization processes during firnification.
Firn is also porous, with the spaces between the grains filled with air. These air-filled pores, or firn air, play a significant role in the study of past atmospheric conditions. As the firn densifies into ice, the air within the pores gets trapped, forming tiny bubbles that preserve samples of the ancient atmosphere.
Role in Glaciology
In glaciology, the study of firn is crucial for understanding the formation and movement of glaciers. Firn is the transitional material between snow and glacial ice. As firn continues to densify under pressure, it eventually turns into glacier ice, contributing to the mass of glaciers.
Firn layers also provide valuable information about past climate conditions. By analyzing the chemical composition and physical properties of firn, scientists can reconstruct past temperatures, precipitation rates, and atmospheric gas concentrations. This makes firn a valuable tool in paleoclimatology, the study of past climates.
Firn Aquifers
One of the interesting phenomena associated with firn is the existence of firn aquifers. These are layers of liquid water that exist within the firn layer in certain parts of the world, particularly in parts of Greenland and Antarctica. The water in these aquifers comes from the melting of surface ice and snow, which then percolates down into the firn layer.
Firn aquifers are of interest to scientists as they can significantly influence the dynamics of ice sheets. The water within these aquifers can lubricate the base of the ice sheet, potentially accelerating its movement towards the sea. This has implications for sea level rise, making the study of firn aquifers important in the context of climate change.