Satellite images acquired between 2017 and 2020 reveal two large landslides over Glaciar Amalia (see location on OpenStreetMaps), an outlet glacier of the Southern Patagonia Icefield terminating on a calving front on the Chilean fjords.

These landslides are pretty massive and spectacular and are apparently originating in a loose deposit of material of volcanic origin (see abstract by de Vries et al, 2019).

The first landslide occurred at some point between March and November 2017. The material originated from a steep, largely unvegetated slope on the southern flank of the glacier. The general morphology and texture of this side of the valley suggests it is probably composed of loose material with low cohesion, making the slope susceptible to landslides and avalanches. As can be seen in the images below (and others not shown here) small debris aprons and fans are almost constantly formed over the side of the glacier right at the foot of the slope and then transported downwards by the glacier.

Glaciar Amalia landslide 2017
Sequence of satellite images from different sensors acquired during the period 2017-2018 showing the landslide over Glaciar Amalia, Chile. Data from Copernicus Sentinel and USGS Landsat.

This landslide resulted in a large main deposit roughly 1.6 km2 in size and a few secondary ones, the largest of which is around 0.3 km2. The probable head scarp of the landslide, together with another minor (later) one, is marked with dotted lines on the image below. Subsequent images show this large accumulation being passively transported down ice towards the calving front.

Incidentally, the snout of Glaciar Amalia is one of those frequently visited by tourists boats sailing the Chilean fjords. Thanks to this, I was able to locate on the internet a very good photograph of the surface deposit as seen from the snout (see here, credit: Bill Holmes).

Glaciar Amalia landslide 2018
Subset of Landsat 8 OLI image aquired on 2018-03-27 showing the landslide deposit on the surface of Glaciar Amalia.

Around 2 years after this large landslide another one, arguably more spectacular, occurred. This time a large portion of the same flank seems to have flowed down in a manner resembling an earth flow. Most strikingly, this has apparently not resulted in a debris deposit on the surface of the glacier, but has seemingly pushed forwards parts of the glacier ice, generating a large zone of thrusted and piled up ice. This accumulation is about 1.6 km2 in area. Unfortunately, the steep nature of the valley walls and the timing of the image, during the late southern autumn, results in the features of interest being partly shadowed (remember that the Sun shines from the North in the Southern hemisphere).

Glaciar Amalia landslide 2019
Subset of Sentinel 2B image acquired on 2019-05-08 showing the landslide deposit on the flank of Glaciar Amalia and the associated mass of thrusted surface ice.

The image sequence below shows that this event took place at some time between March and May 2019. It is evident how the slope morphology has been completely changed. The glacier surface also seems to “heal” relatively quickly after the event, leaving some segmented “scars” and debris, but mostly reacquiring its general shape. This is a wonderful example of plastic deformation of ice, one of the main mechanisms of glacier flow (the others being sliding and deformation of subglacial sediments).

Glaciar Amalia landslide 2019
Sequence of satellite images from different sensors acquired during the period 2019-2020. The new large landslide on the southern flank of Glaciar Amalia caused an spectacular belt of thrusted up ice upon the surface. Data from Copernicus Sentinel and USGS Landsat.

The origin of these particularly large and spectacular landslides can be mostly ascribed to the occurrence of the relatively loose material on the southern flank of the glacier. However, as observed elsewhere in this type of environments, climate change and glacier retreat are very probably making these phenomena more frequent. This is partly because the reduction in volume of glaciers leaves steep unstable slopes free to move, and also because warming is increasing the incidence of melt events on the slopes, with the concomitant mechanical weakening of sediments and loose material. In addition, the relative increase in the frequency of rainfall events, as opposed to snowfall, may also be important in an marine environment like the Southern Patagonia Icefield.

Thanks for reading.