Glaciological methods such
as geodetic surveying, detailed topographic mapping and mass balance determinations
provide direct data about changes in volume, surface area and length of
the glacier over as much as 120 years.
Since about 1890 to the present, the continuously reducing
tongue-length of numerous alpine glaciers has been precisely measured
every year, providing exceptional records especially for the 20th century.
Due to the fact that the so-defined retreat of the glacier tongue covers
a good part of the previous variability range during the last 10000 years,
evidence from earlier times can be related to stages measured in modern
times.
For more see Glacial
processes.
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