northern patagonia ice cap melt – From a Glaciers Perspective

Landsat image comparison 1987 and 2015
Loriaux and Casassa (2013) examined the expansion of lakes of the Northern Patagonia Ice Cap. From 1945 to 2011 lake area expanded 65%, 66 square kilometers. Rio Acodado has two large glacier termini at its headwater, HPN2 and HPN3. that are fed by the same accumulation zone and comprise the Acodado Glacier. The glacier separates from Steffen Glacier at 900 m. The lakes at the terminus of each were first observed in 1976 and had an area of 2.4 and 5.0 square kilometers in 2011. (Loriaux and Casassa, 2013). Willis et al (2012) noted a 3.5 m loss per year from 2001-2011 in the ablation zone of the Acodado Glacier, they also note annual velocity is less than 300 m/year in the ablation zone. Davies and Glasser (2012) noted that the Acodado Glacier termini, HPN2 and HPN3, had retreated at a steadily increasing rate from 1870 to 2011. Here we examine the substantial changes in Acodado Glacier from 1987 to 2015 using Landsat imagery.
Digital Globe image of Acodado Glacier and the termini HPN2 and HPN3.

In HPN2 terminates at the red arrow in 1987 and HPN3 at the yellow arrow, the snowline is at the purple dots at 1000 m. By 2000 the glacier has retreated from the red and yellow arrow by 400 m and 900 m respectively, and the snowline is at 1100 m. In 2014 there are many large icebergs in the lake at the terminus of HPN3, these are from recent calving retreat. This is not an area where the lakes develop even seasonal lake ice cover. The snowline is again at 1100 m. In 2015 it is apparent that HPN2 has retreated 2100 m from the red arrow to the pink arrow. HPN3 has retreated 3200 m from the yellow to the orange arrow. The snowline is again at 1100 m. The retreat accelerated after 2000 for both glaciers. This high of a snowline indicates warm temperatures generating high ablation rates, which will lead to more retreat. HPN3 has a sharp rise in elevation 2.5 km above the terminus, before it joins the main Acodado Glacier, it should retreat rapidly toward this point and then calving will end and retreat will slow. The retreat here is synonymous with the pattern observed at other Northern Patagonia Ice Cap outlet glaciers each with rapid calving retreats in expanding proglacial lakes; Fraenkel Glacier, Gualas and Reichert Glacierand Steffen Glacier.

Landsat image from 1987

Landsat image from 2000

Landsat image from 2014

Landsat image from 2015

Fraenkel Glacier drains the west side of the Northern Patagonia Ice Cap (NPI) just south of Glaciar San Quintin. The retreat of this glacier in the last 30 years mirrors that of Gualas and Reichert Glacier, which also terminate in an expanding proglacial lake. Davies and Glasser (2012) work, had an excellent Figure indicating two periods of fastest recession since 1870, are 1975-1986 and 2001-2011 for NPI glaciers. They noted the loss was 0.07% from 1870-1986, 0.14% annually from 1986-2001 and 0.22% annually from 2001-2011. Willis et al (2011) observed that the thinning rate of NPI glaciers below the equilibrium line has increased substantially from 2000-2012. On Fraenkel Glacier they observed a 2.4 m per year thinning in the ablation zone. Here we examine the changes in this glacier from 1987 to 2015 using Landsat Image.

In 1987 the glacier terminus was at the end of a peninsula red arrow and the proglacial lake it terminates in is 2 km long. There is a medial moraine on the glacier at the yellow arrow and the glacier covers the terrain below an icefall at the purple arrow. By 2000 at the purple arrow bedrock is appearing from the base of the glacier. The medial moraine at yellow arrow is little changed. The terminus has retreated 800 m. By 2015 the area around the purple arrow has been deglaciated emphasizing the amount of thinning in the ablation zone even well upglacier of the terminus. At the yellow arrow the medial moraine has been replaced by a wide rock rib separating the glacier from a former tributary. The main terminus is at the pink arrow, indicating a retreat of 1.4 km since 1987. The retreat rate of 50 meters per years though large is less than on Reichert Glacier or Gualas Glacier. Mouginot and Rignot (2014) observe that Fraenkel Glacier does not have the high velocity of the neighboring Benito and San Quintin Glacier or the Gualas and Reichert Glacier, this leads to the potential for greater mass loss of the ablation zone and even faster retreat.

Fraenkel Glacier Landsat Image 1987

Fraenkel Glacier Landsat Image 2000