Nearctic Glacier and Scree - Code: Ne10G

Found in the high latitudes of the Arctic and towering mountain peaks further south, Glacier and Scree is one of the most visually stunning habitats found on the continent. This habitat is structurally comprised of two principal elements – permanent, slow-moving bodies of dense ice (glaciers) and loose fields of loose, broken, rock (scree). There are glaciers without scree and scree without glaciers but the conditions required for each are frequently co-occurring. Despite their related nature it is easier to talk about the dynamics and formation of each of the two aspects separately. 
The term scree is applied both to an unstable steep mountain slope composed of rock fragments and other debris, and to the mixture of rock fragments and debris itself. For our purposes, scree also refers to talus (material directly at base of a rock face) and colluvium (material transported by gravity downslope), which are slightly different processes with the same end result – a big pile of rocks. Glacial scree occurs in areas that are mechanically unstable because plant growth is particularly slow in these frigid environments. This means scree typically forms in areas that are either particularly cold or particularly dry. In the case of co-occurrence with glaciers it is almost always the former. 
Scree can accumulate to an extent where it halts the movement of the source material. When this happens the scree or talus stabilizes and eventually will degrade and be covered by encroaching vegetation. However, the presence of glaciers provides constant disturbance via glacial movement and glacial run-off that keeps scree slopes from stabilizing and degrading. Weathering of scree is almost entirely mechanical. That is, it is broken down bit by bit through abrasion, frost fracturing and other physical processes. Frost fracturing is when water enters miunte cracks in rocks and freezes. The roughly 9% increased in volume fractures the rock a little. In periods of fluctuating freeze-thaw activity, the process is repeated often with dramatic effect- think frozen pipes here. Now in extreme climate such as the High Arctic, this process is not as common because temperatures remain below freezing for many months on end, and in polar deserts, it is not appreciable due to a lack of water to freeze. 
In contrast to more tropical environments, chemical weathering is extremely limited. The lichens and other growth that occurs here create its own nutrient source through biotic breakdown rather than the uptake of soil nutrients from rocks. This may seem esoteric, but it means that the soils that form on these deposits usually have very little relationship to the underlying geological parent material, something which is a major habitat determinant in warmer environments. 
The formation of glaciers is simple – the amount of snow accumulating needs to exceed the amount of snow lost on an annual basis, so that compaction occurs . There is no single combination of altitude, latitude, temperature, or precipitation that produces a glacier but typically, you can expect this habitat to have extremely cold, snowy winters and relatively low temperatures in the summer. Many areas that seem like they should hold glaciers are simply too dry, and vast areas of the Arctic remain an ice-free Polar Desert.
In a growing glacier, snow accumulates over many years and is compressed into dense glacial ice. As the weight of snow and ice builds at the head of the glacier, it will begin to flow downward, literally at a glacial pace, or outward through a geological weakness; often a gap in the mountains, while scouring new paths, through abrasion of the underlying rock and creating dramatic landscapes such as U shaped valleys, hung valleys, and cirques. Many glacial flows slowly diminish as they move downslope, but some terminate more dramatically as they flow directly into the sea. Such glaciers are called tidewater glaciers and their sudden end produces spectacular ice walls and a constant stream of icebergs. The calving of tidewater glaciers is a minor source of sea ice found in Arctic Pelagic Waters.
While mixed areas of glacier and scree can be utilized by wildlife, massive glaciers generally cannot. When conditions appropriate for glacier formation occur over large contiguous areas it leads to the formation of ice sheets. Ice sheets cover a minimum of 50,000 km² (19,000 mi²) and can be several kilometers thick. In modern times ice sheets are only found in polar regions but during the last glacial maximum (~20,000 years ago) the Laurentide Ice Sheet covered 13 million km² (5 million mi²) and stretched as far south as Indianapolis! The remnants of this massive ice sheet still exist today on Greenland.