Chile proglacial lake retreat – From a Glaciers Perspective

Ofhidro Glacier glacier terminus change an accumulation zone changes from 1986-2019 in Landsat images. Red arrow=1986 terminus, yellow arrow=2019 terminus change, orange arrows expanding bedrock areas and purple dots snowline.

Ofhidro Glacier is an outlet glacier on the northwest corner of the Southern Patagonia Icefield (SPI), that has a northern and southern arm terminating in a proglacial lake. Sakakibara and Sugiyama (2014)a examine the terminus change and velocity of SPI glaciers the northern arm retreating 50 m per year from 1985-2011 and the southern arm 100 m/year 1985-2011. They also noted a decline in velocity Here we examine Landsat imagery from 1986-2019 to identify the change.

In 1986 the southern arm extended across the proglacial lake to the shallows of the western shore. The northern arm had been retreating in a narrower valley with a comparatively consistent width. In 1998 the southern arm in the broader lake reach had collapsed, a retreat of 1800 m. The northern arm had a retreat of 200 m. The snowline was at m. In 2015 the southern arm has retreated into a narrower valley, and the northern arm has retreated to a turn to the south in the valley. The orange arrows indicate the expansion of bedrock as the glacier thins. By 2019 the southern arm has retreated 2800 m (88 m/year) and the northern arm has retreated 1800 m (56 m/year). Jaber et al (2019) noted a thinning of 0.5 m/year from 2000-2012 increasing to 1.2 m/year from 2012-2016. Most of the thinning being in the valley tongues of each arm. There is an area of continuous exposed bedrock more than 3 km long. This fits the observations of Willis et al (2012) who observed that between February 2000 and March 2012 that SPI was rapidly losing volume and that thinning extends even to high elevations. The retreat of this glacier is similar to that of Lucia Glacier and Gabriel Quiroz Glacier to the east.

Ofhidro Glacier glacier terminus change an accumulation zone changes from 1998-2015 in Landsat images. Red arrow=1986 terminus, yellow arrow=2019 terminus change, orange arrows expanding bedrock areas and purple dots snowline.

Ofhidro Glacier image from 2015. Notice the trimlines and narrowing of both terminus tongues. Orange arrow indicates new bedrock knob.

Cachalote Glacier in a 1984 Landsat image and 2019 Sentinel Image. Red arrow is 1984 terminus location, yellow arrow the 2019 terminus location and the pink arrow a tributary to the glacier in 1984 that separates.

Cachalote Glacier is on the western edge of the Southern Patagonia Icefield, Chile. The glacier is not fed by the main icefield, but is connected to glaciers that are. The glaciers of the SPI have been experiencing significant mass loss and overall retreat. Willis et al (2012) observed significant mass loss from 2000-2012 of −20.0 Gt per year. Davies and Glasser (2012) indicate this area had its most rapid retreat of the 1870-2011 period after 1986.

In 1984 Cachalote Glacier terminated in a proglacial that was ~600 m long, red arrow. The glacier was joined by a tributary from the west ~1 km from the terminus, pink arrow. By 2001 the tributary had separated from the main glacier. The glacier still terminated in the proglacial lake, but had retreated 1.5 km and the proglacial lake was now just over 2 km long. In 2017 the glacier no longer reached the proglacial lake. In 2019 the glacier has retreated 2.6 km from its 1984 position, 30% of its entire length lost in the span of 35 years. The glacier no longer terminates in a lake and ends near the top of a steep slope, both suggest that retreat should decline for the near future.

This is a less spectacular retreat than at HPS-12 Glacier which is a short distance to the norther and is the fastest retreating glacier in the region or Dickson Glacier on the east side of the icefield, but as a percent of glacier length lost is as substantial.

Cachalote Glacier in a 2001 and 2017 Landsat images. Red arrow is 1984 terminus location, yellow arrow the 2019 terminus location and the pink arrow a tributary to the glacier in 1984 that separates by 2001.