| Themes > Science > Earth Sciences > Geology > Water and Water Cycles > Glacier fluctuations |
Brief Description: Changes in glacier movement, length and volume can exert profound effects on the surrounding environment, for example through sudden melting which can generate catastrophic floods, or surges that trigger rapid advances (in the recent surge of the Bering Glacier, Alaska, as much as 12 km in a 60 day period). Standard parameters include mass balance and the glacier length, which determines the position of the terminus. The location of the terminus and lateral margins of ice and rock glaciers exerts a powerful influence on nearby physical and biological processes. Through a combination of specific balance, cumulative specific balance, accumulation area ratio and equilibrium-line altitude, mass balance reflects the annual difference between net gains (accumulation) and losses (ablation). It may also be important to track changes in the discharge of water from the glacier as indicators of glacier hydrology. Abrupt changes may warn of impending acceleration in melting, cavitation, or destructive flooding. Significance: Glaciers are highly sensitive, natural, large-scale, representative indicators of the energy balance at the Earth's surface in polar regions and high-altitudes. Their capacity to store water for extended periods exerts significant control on the surface water cycle. The advance and retreat of mountain glaciers creates hazards to nearby human structures and communities through avalanches, slope failure, catastrophic outburst floods from ice and moraine-dammed lakes. Notwithstanding local glacier advances, the length of mountain glaciers and their ice volume has decreased throughout the world during the past century or two, providing strong evidence for climate warming, though there may also be local correlations with decreasing precipitation. It is estimated that the European Alps have lost more than half their ice in the past century. Human or Natural Cause: Glaciers grow or diminish in response to natural climatic fluctuations. They record annual and long-term changes and are practically undisturbed by direct human actions. Environment Where Applicable: Wherever glaciers and icecaps occur. Types of Monitoring Sites: Selected glacier forelands and icecaps strategically located to record climate changes, or liable to rapid advances/retreats that may affect fluvial systems or nearby settlements. Spatial Scale: patch to mesoscale / continental Method of Measurement: Analysis of air photos and high-resolution satellite images, ground surveys. GPS data may be useful in detecting glacial surges and estimating the volume of ice being transferred. Frequency of Measurement: Annually, more frequently where glaciers are surging. Limitations of Data and Monitoring: The monitoring of continental glaciers, such as the Antarctic and Greenland ice sheets, is a complex matter, and there is no easy technique for detecting volume changes that will affect sea levels. Horizontal advances or retreats of an ice sheet margin may not provide timely information on volume changes, and field studies of mass balance can never adequately cover the entire ice sheet. Applications to Past and Future: Changes in glaciers in areas of high snowfall may provide early clues to the onset of climate change. Ice and air bubbles trapped between ice crystals in glaciers and ice-sheets provide an invaluable archive of past climates, which extends, in Greenland, the Antarctic and certain mountain glaciers, well back into the Pleistocene. They also contain a record of past changes in atmospheric composition, including trace gas concentrations, chemical impurities of terrestrial and marine origin, cosmogenic isotopes, extraterrestrial material, and aerosols of volcanic, desert and human origin. The chronostratigraphy of snow-avalanche deposits may also be an important source of paleoclimate information (snowfall, wind) in mountain areas. |
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