Advance and retreat. A series of concentric moraines in front of the terminus of the Kluane Glacier in Alaska's St. Elias Mountains record advances and retreats of this glacier during the past several thousand years.
LA foto è stata scattata il 10 agosto 1961The photo shown here was taken on 10 August 1961. In 1973, Denton and Karlen showed that moraines in this region of Alaska had similar ages as others in Scandinavia and proposed that glaciers worldwide had advanced and retreated together in response to changes in solar irradiance (2). Subsequent research, including the report in this issue by Schaefer et al., has neither proved nor disproved this hypothesis but rather has revealed the complexity of past climate changes and the response of glaciers to these changes.
Balco G. The Geographic Footprint of Glacier Change. Science 2009; 324: 599.
Immagine: Austin Post/US Geophysical Institute/Universtity of Alaska Fairbanks