United States Geological SurveyThe United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the United States government whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on March 3, 1879, to study the landscape of the United States, its natural resources, and the natural hazards that threaten it. The agency also makes maps of extraterrestrial planets and moons based on data from U.S. space probes.
Glacier ice accumulationGlacier ice accumulation occurs through accumulation of snow and other frozen precipitation, as well as through other means including rime ice (freezing of water vapor on the glacier surface), avalanching from hanging glaciers on cliffs and mountainsides above, and re-freezing of glacier meltwater as superimposed ice. Accumulation is one element in the glacier mass balance formula, with ablation counteracting. With successive years in which accumulation exceeds ablation, then a glacier will experience positive mass balance, and its terminus will advance.
ArêteAn arête (əˈrɛt ) is a narrow ridge of rock that separates two valleys. It is typically formed when two glaciers erode parallel U-shaped valleys. Arêtes can also form when two glacial cirques erode headwards towards one another, although frequently this results in a saddle-shaped pass, called a col. The edge is then sharpened by freeze-thaw weathering, and the slope on either side of the arête steepened through mass wasting events and the erosion of exposed, unstable rock.
Pyramidal peakA pyramidal peak, sometimes called a glacial horn in extreme cases, is an angular, sharply pointed mountain peak which results from the cirque erosion due to multiple glaciers diverging from a central point. Pyramidal peaks are often examples of nunataks. Glaciers, typically forming in drainages on the sides of a mountain, develop bowl-shaped basins called cirques (sometimes called ‘corries’ - from Scottish Gaelic coire [khəɾə] (a bowl) - or cwms).
TributaryA tributary, or affluent, is a stream or river that flows into a larger stream or main stem (or parent) river or a lake. A tributary does not flow directly into a sea or ocean. Tributaries and the main stem river drain the surrounding drainage basin of its surface water and groundwater, leading the water out into an ocean. The Irtysh is a chief tributary of the Ob river and is also the longest tributary river in the world with a length of . The Madeira River is the largest tributary river by volume in the world with an average discharge of .
Terminal moraineA terminal moraine, also called an end moraine, is a type of moraine that forms at the terminal (edge) of a glacier, marking its maximum advance. At this point, debris that has accumulated by plucking and abrasion, has been pushed by the front edge of the ice, is driven no further and instead is deposited in an unsorted pile of sediment. Because the glacier acts very much like a conveyor belt, the longer it stays in one place, the greater the amount of material that will be deposited.
Proglacial lakeIn geology, a proglacial lake is a lake formed either by the damming action of a moraine during the retreat of a melting glacier, a glacial ice dam, or by meltwater trapped against an ice sheet due to isostatic depression of the crust around the ice. At the end of the last ice age about 10,000 years ago, large proglacial lakes were a widespread feature in the northern hemisphere. The receding glaciers of the tropical Andes have formed a number of proglacial lakes, especially in the Cordillera Blanca of Peru, where 70% of all tropical glaciers are.
SnowpackSnowpack forms from layers of snow that accumulate in geographic regions and high elevations where the climate includes cold weather for extended periods during the year. Snowpacks are an important water resource that feed streams and rivers as they melt. Therefore, snowpacks are both the drinking water source for many communities and a potential source of flooding (in case of sudden melting). Snowpacks also contribute mass to glaciers in their accumulation zone.
BergschrundA bergschrund (from the German for mountain cleft) or rimaye (from French; ʁimaj) is a crevasse that forms where moving glacier ice separates from the stagnant ice or firn above. It is often a serious obstacle for mountaineers, who sometimes abbreviate "bergschrund" to "schrund". Bergschrunds extend to the bedrock and can have a depth of well over . A bergschrund is distinct from a randkluft (also called rimaye), which is a crevasse with one side formed by rock.
HeadwallIn physical geography and geology the headwall of a glacial cirque is its highest cliff. The term has been more broadly used to describe similar geomorphic features of non-glacial origin consisting of a concave depression with convergent slopes typically of 65 percent or greater forming the upper end of a drainage valley. In civil engineering, a headwall is a small retaining wall placed at the inlet or outlet of a stormwater pipe or culvert. In medicine, a headwall is the wall at the head end of a hospital bedspace.
