by Gwynne Leavitt ’14
Located high in the mountains, alpine glaciers are formed by the downhill movement of perennially thick snow and ice. There are a number of different types of glaciers, including cirque, valley, ice cap, fjord, and piedmont glaciers. The upper zone of glaciers are called accumulation areas, where the glaciers gain mass from new snow, while the lower zones are called ablation areas, where they lose mass from the melting of exposed ice and snow. For a glacier to remain at a constant size, both the accumulation and ablation must equal one another, while for a glacier to decrease in size the rate of ablation must be bigger than the rate of accumulation. This concept of mass balance is very important to the survival of a glacier, especially with increasing temperatures as a result of climate change.
The terminus of the glacier is the front of the glacier, and it advances or retreats depending on the mass balance, though in either case the glacier moves downhill. The area of the glacier where mass is neither gained nor lost is the equilibrium line, which is located between the zone of ablation and accumulation. Moraines are areas where glacial debris is deposited and they occur both on the sides of glaciers (lateral moraine) and in the middle of a glacier (medial moraine) in the case of the junction of two tributary glaciers. Crevasses form when the brittle top layer of the glacier cannot bend and cracks form while the plastic bottom layer of the glacier flows over bedrock obstacles . Important water features of glaciers include supraglacial streams (meltwater surface streams that form during summer melt), subglacial lakes (water filled caverns within the ice), and moulins (circular shafts that bring surface water through the glacier, often to the base where it encourages basal sliding of the glacier over the land surface..
The recent increase in glacial melt water due to climate change may directly affect the thermohaline circulation system of the ocean. The Younger Dryas Stadial, a cold period about 11,700-12,900 years ago-resulted from large amounts of cold, fresh melt water emptying into the Atlantic Ocean. A 2010 scientific study on glaciers in the New Zealand Southern Alps supported the idea that melt water from glaciers could possibly affect the thermohaline circulation system, and thus lead to a cold trend. Glacial impacts on other spheres of the Earth system include: maintaining global temperature, creating environments where primary succession can occur, and acting as tributaries for larger valley rivers.
 Kirkbride, P. Martin. “Climate Change: A Glacial Test of Timing”. Nature. September 8, 2010. Viewed March 12, 2014. http://www.nature.com/nature/journal/v467/n7312/full/467160a.html