Glacier Equilibrium Line Research Articles

Climate at the Equilibrium Line of Glaciers

AbstractThe relationships between temperature, precipitation and radiation on glacier equilibrium lines are investigated, using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods. It is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months’ temperature in a free atmosphere, annual total precipitation, and the sum of global and long-wave net radiation. All of these are measured at or very near the equilibrium-line altitudes. Then, it is shown how the shift of the equilibriumline will occur as a result of a climatic change. Finally, the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations. The present results make it possible to identify the altitudes in climate models where glacierization should begin, and to evaluate the mass-balance changes as a result of possible future changes in the climate.

Climate at the Equilibrium Line of Glaciers

AbstractThe relationships between temperature, precipitation and radiation on glacier equilibrium lines are investigated, using 70 glaciers for which the mass balance and meteorological observations have been carried out for sufficiently long periods. It is found that the characteristic climate at glacier equilibrium lines can be described using the summer 3 months’ temperature in a free atmosphere, annual total precipitation, and the sum of global and long-wave net radiation. All of these are measured at or very near the equilibrium-line altitudes. Then, it is shown how the shift of the equilibriumline will occur as a result of a climatic change. Finally, the effect of the shift of the equilibrium line on the annualmean specific mass balance is analytically derived and compared with observations. The present results make it possible to identify the altitudes in climate models where glacierization should begin, and to evaluate the mass-balance changes as a result of possible future changes in the climate.

Climatic Change in the Colorado Rocky Mountains: Estimates Based on Modern Climate at Late Pleistocene Equilibrium Lines

A comparison of modern climates at late Pleistocene glacier equilibrium lines in the Colorado Rocky Mountains with the range of climates which occur at the equilibrium lines of modern glaciers worldwide allows an evaluation of the combinations of temperature and precipitation change which would have been necessary to sustain the late Pleistocene glaciers. Modern climatic conditions at late Pleistocene equilibrium lines at 12 sites in 7 ranges are approximated using instrumental and snow survey data. The comparison provides paired values of temperature and precipitation changes which would maintain the glaciers at their late Pleistocene maximum positions. If no change occurred in total precipitation or in seasonal distribution of precipitation between the late Pleistocene and the present, an approximately 8.5?C summer temperature depression would have been necessary to sustain the late Pleistocene glaciers. A 10 to 13?C late Pleistocene temperature depression, which has been suggested on the basis of other lines of evidence, would have been accompanied by a reduction of at least 44%o in fall-through-spring precipitation compared to present-day values.

Topography as a fundamental element of glacial systems

The equilibrium line of glaciers as a climate-sensitive parameter is indispensable for the assessment of changes in climate through time. The methods previously developed for calculating the equilibrium line do not obtain, however, satisfactory accuracy. Using the statistical evaluation of data collected from 223 glaciers it is shown here that the inaccuracy of the prevailing methods results from the negligence of the specific glacier geometry.

Pleistocene glaciation in the southern Lake District of Chile

Relative-age criteria permit deposits of successive Andean glacier advances in the southern Lake District of Chile to be divided into four mappable drift sheets, the oldest two of which overlie Tertiary bedrock along the eastern flank of the Cordillera de la Costa. Only the youngest drift (Llanquihue) is datable by radiocarbon. During the most extensive ice advance of the last glaciation the Lago Llanquihue glacier was about 95 km long and reached an estimated maximum thickness of between 1000 and 1300 m. Glacier equilibrium lines at that time lay about 1000 m below their present level and rose eastward with a gradient of about 5 m/km. Successive ice advances in the Lago Llanquihue basin, which resulted in construction of end moraines and associated outwash plains beyond the lake margin, culminated sometime before about 20,000 yr ago and between 20,000 and 19,000 yr ago. A later readvance, inferred from the sedimentary record of lake-level fluctuations in the basin, had begun by about 15,000 yr ago and culminated shortly after 13,000 yr ago. A comparable, but less-closely dated, record of ice advances is found northwest of Seno Reloncaví and on Isla Chiloé. Deglaciation following the latest advance is likely to have been rapid, for the major glacier lobes fronted on deep water bodies that would have promoted extensive calving.