The Physics of Glaciers

Glacier Zones

Each glacier, no matter the type, shares the same general characteristic zones. The accumulation zone is located at the top of the glacier, where the amount of snowfall is greater than the amount of snow melt. The ablation zone on the other hand occurs when the snow melt exceeds the amount of accumulation, it is also commonly called the zone of wastage. (“Seminar…”) These two zones are the most general characteristics of glaciers, and have an equilibrium line between them where the amount of snowfall equals the snow melt. This line is dependent entirely on the climate, and can be used to estimate the fraction of a glacier losing mass. The line is visible in the summer where the ice turns from snow-covered to exposed. (Fountain)

 
Photo of Worthington Glacier, the blue, exposed ice is the ablation zone while the accumulation zone sits above it in the distance. In the middle of the photo sits a moraine formed from the splitting of the glacier, a term covered in the next section.

The Ablation Zone

Within the ablation zone of a glacier there exist certain divisions, such as the moraine, which contains rock and debris that the glacier has pushed downwards over time. According to Dr. Andrew G. Fountain from the Portland University department of geology, “Eventually, this debris is deposited at the end of the glacier or along its sides forming a ridge called a moraine. When the ridge forms on the side of a glacier, it is called a lateral moraine. When it forms at the lower end of the glacier, the terminus, it is called a terminal moraine” (Fountain). At this terminus, or end of the glacier, snow and ice melt flows into glacial streams, which appear silty. Silt is a result of rocks being ground down into a very fine sediment by the pressure of the glacier movement. Fountain explains that this silt is from the movement of a glacier, “A glacier is sort of like sandpaper, except the rocks are carried in the ice. As a glacier moves down hill, it plucks rocks from the bedrock and carries them along the base grinding them back into the bedrock” (Fountain). The grinding down of these rocks disintegrates them to a powdery texture which is carried by the melt of the glacier to the streams.


(Fountain)

The Accumulation Zone

Underneath the accumulation zone there are three main layers, snow, ice, and firn. Snowflakes themselves are spread out with space in between their molecules. In order for snow to become packed ice, it undergoes a transformation from snowflake, to firn, and then to ice. (Fountain) In the accumulation zone, a glacier appears snowy, and ice is not exposed. The equilibrium line on a glacier divides the two zones discussed, and can be identified as the division between a glacier appearing snowy in the accumulation zone, and then with exposed ice in the ablation zone.