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NAME: Glacier fluctuations
(With contributions by A. Nesje, and M. Demuth. Revised February 2005)
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, which reflects the volume of ice, and 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 (glacial outbursts).
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. Mass balance measurements can help to put contemporary climate change into a longer-term perspective, especially via ice cores. The capacity of glaciers to store water for extended periods exerts significant control on the surface water cycle. During periods of warm weather and intense sunlight, glaciers melt vigorously and provide a water source for the surrounding ecosystems and communities: during cold seasons, glaciers produce less meltwater. These fluctuations can affect agriculture, drinking water supplies, hydroelectric power, transportation, tourism, coastlines, and ecological habitats. The advance and retreat of mountain glaciers can create hazards to nearby settlements through landslides and outburst floods from ice and moraine-dammed lakes. These can destroy property and lives in a sudden rush of water, ice, sediment, rock, soil, and debris.
Notwithstanding local glacier advances, most of the world.s glaciers are either stagnant or in rapidly retreating, in response to climate change. These changes are expected to accelerate over the coming century as climate warming increases. Indeed, the decreasing length and mass balance of mountain glaciers throughout the world during the past century or two, provides strong evidence for climate warming, though there may also be local correlations with decreasing precipitation. The release of water stored in ice sheets and glaciers has a profound effect on global sea levels, the freshwater budget of the Arctic Basin and marine and terrestrial aquatic resources. The detection of chemical constituents in ice cores puts modern pollution into a much-needed temporal perspective and can assist in monitoring of international protocols.
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 ice sheets occur.
TYPES OF MONITORING SITES: Selected glacier forelands and ice caps strategically located to record climate changes or liable to rapid advance or retreat in ways that can affect fluvial systems or nearby settlements.
SPATIAL SCALE: patch to mesoscale / continental
METHOD OF MEASUREMENT: Analysis of air photos and high-resolution satellite images (e.g. ASTER) and 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. Mass balance measurements are usually conducted seasonally, whereas variations in ice margins, thickness and volume are assessed according to the rate of change.
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 glacier and ice sheet margins may not provide timely information on volume changes, and field studies of mass balance can never adequately cover an entire ice sheet. Glaciers of different size and climatic situation will respond differently to a change in their mass, so that the interpretation of meaningful trends must use observations from groups of glaciers similar in size, typology and regional climatic setting. Remote sensing techniques are increasing the capacity to track changes, especially in ice sheets and large ice caps.
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.
Retreat of outlet glaciers into over-deepened basins and the formation of terminal lakes may create sudden shifts in the hydrological regime, including thermal and hydraulic properties of glacier-fed streams. Glacier surges can block rivers to form lakes which may then burst when water pressure exceeds strength of the ice barrier.
Haeberli, W., M. Hoelzle & S. Suter (eds) 1998. Into the second century of worldwide glacier monitoring - prospects and strategies. Studies and Reports in Hydrology 56. Paris: Unesco Publishing, 227p.
Hambrey, M. 1994. Glacial environments. London, UCL Press.
Matthews, J.A., 1992. The ecology of recently-deglaciated terrain: a geoecological approach to glacier forelands and primary succession.Cambridge University Press.
Anon: 1988 and in progress. Satellite Image Atlas of Glaciers of the World. USGS Professional Paper 1386.
UNEP/GEMS, 1992. Glaciers and the environment. United Nations Environment Programme, Environment Library 9.
OTHER SOURCES OF INFORMATION: Changes in the extent, movement and mass balance of glaciers have been monitored internationally since 1894, a task now coordinated by WGMS (the World Glacier Monitoring Service (http://www.geo.unizh.ch/wgms/). Global Land Ice Measurements from Space (http://www.glims.org/), International Commission on Snow and Ice (http://www.glaciology.su.se/ICSI/). World Data Center for Glaciology (http://nsidc.org/wdc/)
RELATED ENVIRONMENTAL AND GEOLOGICAL ISSUES: Glacier melting can sometimes trigger catastrophic flood outbursts (jökulhlaups) from marginal lakes blocked by moraines, though failure of these natural dams may have a variety of other causes. The decreasing capacity of retreating glaciers to store water affects downstream water supply and availability of water for agriculture and human consumption. Glacier forelands newly exposed in front of receding glaciers provide excellent natural laboratories to study plant succession and soil development.
OVERALL ASSESSMENT: Fluctuations in glaciers are among the most sensitive indicators of climatic change. They can be also used as indicators of temperature and precipitation changes that occurred prior to instrumental weather records. Glacier fluctuations are key indicators of climate variability and freshwater resource, such as streamflow. Ice sheets play a significant role in defining surface albedo and land-ocean-atmospheric processes.
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