November 12, 2010

Glacier Nef Retreat, Rio Baker, Chile

Posted by Mauri Pelto

Glacier retreat and thinning is particularly strong in the Patagonian icefields of South America. The two largest temperate ice bodies of the Southern Hemisphere are the Northern Patagonia Icefield (CHN image below) 4,000 km2 and the Southern Patagonia Icefield (CHS), 13,000 km2. It has been estimated that the wastage of the two icefields from 1995–2000 has contributed to sea level rise by 0.105 ± 0.011 mm year,which is double the ice loss calculated for 1975-2000 (Rignot et al. 2003).Nearly 90% of the glaciers studied are affected. Of the 72 glaciers surveyed in the region 63 have retreated significantly, only eight have remained stable and one advanced. O’Higgins Glacier, which feeds the Pascua River has retreated 11.6 km, IRD, 2010. Baker River (Rio Baker) is located to the east of the Northern Patagonia Icefield and is fed mainly by glacier melt water originating from the eastern outlet glaciers of the iecefield Leones, Soler, Nef, Colonia. Rio Baker is the most important Chilean river in terms of runoff, with an annual mean discharge of about 1000 m3/s . Glacier Nef is one of the main glaciers feeding Rio Baker. Rio Baker is a critical hydropower resource for Chile. Hidroaysen Project is proposing 5 dams on the Baker and Pascua River generating 2750 MW of power. Update:  Thee proposed dams have been cancelled. Glacier Nef retreated 3400 m from 1945-2000, 2400 m retreat of the retreat occurred in the 1994 collapse of the terminus tongue into the proglacial lake, which is now 3.5 km long as seen in the image from Pierre Chevallier IRD. The glacier has an area of 164 km2 the proglacial lake began to from after 1945, but was less than 1 km long until after 1994. The glacier had primarily been thinning in height and width near the terminus from 1945-1994
(Aniya, 1986 ) and Winchester, et al. (2010). Below is a map of the hydropower project, from Hidroaysen Project. Today Glacier Nef has not reached the head of this proglacial lake and will continue to retreat. The west side of the terminus is debris covered and has a fringing proglacial lake. The lack of elevation change and the isolated proglacial lake here suggests the lake will expand laterally as well as length wise. The retreat follows the pattern of enhanced calving in a proglacial lake for NPI glaciers such as Gualas GlacierReichert Glacier, Steffen Glacier, and Colonia Glacier. The retreat via calving due to a thinning terminus tongue is similar to the case on Gilkey Glacier, Alaska, Tasman Glacier, New Zealand and Triftglestcher, Austria. The visible trimline indicates the thinning. The lack of vegetation indicates the recent nature of the retreat from this lateral trimline. The glaciers feeding Rio Baker remain quite large and will remain a large meltwater source for the forseeable future. The majority of Glacier Nef is above the recent equilibrium line altitude of 1200 m. The section of the Rio Baker below is where one of the dams will go.