November 21, 2016

RG150 Glacier Retreat, Southern Patagonia Forms Lake

Posted by Mauri Pelto

 

peel-landsat-compare

Retreat of RG150 indicated in Landsat images from 1984, 2001 and 2015.  Red arrow indicates 1984 terminus and yellow arrow 2015 terminus. 

RG150 is a 3.5 km long glacier in Bernardo O’Higgins National Park on the western edge of the Southern Patagonia Icefield, Chile.  RG150 is an unnamed glacier given this designation as part of the Randolph Glacier Inventory.  The glacier terminates in a lake that drains into Seno Andrew.  Willis et al (2012) observed that between February 2000 and March 2012 that the Southern Patagonia Icefield is rapidly losing volume and that thinning extends even to high elevations.  The mass balance loss is occurring at a rate of −20.0 ± Gt/year, which is +0.055 mm/year of sea level rise. The retreat has been driven by increasing calving rates from the 1975-2000 to the 2000-10 period (Schaefer et al, 2015). The pattern of retreat is consistent between these glaciers and the region as noted by Davies and Glasser (2012), annual rates of shrinkage in the Patagonian Andes increased in from 0.10% year from 1870-1986, 0.14% year from 1986-2001, and 0.22% year from 2001-2011. Davies and Glasser (2012), note the all the glaciers in the complex inclusive of RG150 had their fastest retreat period from 2001-2015. Glasser et al (2016) observed both an increase in glacier proximal lakes and in debris cover on glaciers with glacier retreat from 1987-2015. These losses have led to retreat such as at Balmaceda Glacier,  Glaciar Marconi and Glacier Onelli.  Here we examine Landsat imagery from 1984 to 2015 to identify glacier change and the formation of a new lake.

In 1984 there was no glacier lake at the terminus, with the lower 1 km of the glacier being a low sloped glacier tongue.  By 2001 a small proglacial lake had developed 250-300 m long.  In 2005 the glacier retreat had led to continued lake expansion.  The glacier had filled the lake with numerous small icebergs.  By 2015 the glacier still terminates in the proglacial lake that is not 850-900 m long.   The glacier retreat of 850 m since 1984 is 20-25% of the total glacier length.  The low slope region is minimal in length in 2015 indicating the lake basin is almost complete.  This will lead to a reduced rate of retreat.  This is a very cloudy region, and the images here are not at the end of the melt season.  Hence, the equilibrium line altitude can be ascertained.  At the crest of the glacier 1300 m, there are a number of wind sculpted features that are 400-600 m long, attesting to the strong westerly winds in the region. RG150 has significant retained accumulation each year and can survive the current climate.

peel-ge-compare

Retreat of RG150 indicated in Google Earth images from 2005 and 2015.  Red arrow indicates 1984 terminus and purple arrows indicate wind features at the top of the glacier.

peel-oblique

RG150  in Google Earth image looking upglacier in 2015.  Red arrow indicates 1984 terminus and yellow arrow 2015 terminus and purple arrows indicate wind features at the top of the glacier.