twitcher glacier retreat – From a Glaciers Perspective

Twitcher Glacier in Landsat images from 1989 and 2019. The red arrow is the 1989 terminus and yellow arrow is the 2019 terminus. 1, 2 and 3 are tributaries.

In 1989 this glacier terminated approximately at the end of a peninsula separating the two glaciers. Here we examine Landsat imagery from 1989, 2002, 2015 and 2019 to identify the rate retreat. The 1989 terminus position is indicated with the down pointing red arrow and the 2019 terminus position with a yellow arrow. The retreat is less than 0.5 km from 1989-2002. Three tributaries from the south side are feeding the main glacier in 1989 and in 2002. By 2015 the glacier has retreated a further 1.7 km retreat and tributary #1 now flows directly into the expanding Twitcher Bay. By 2019 tributary #2 has detached from the glacier as well. The glacier retreat from 1989-2019 has been 5.2 km, which is 40% of its 12 km length in 1989. last image is a closeup in Google Earth from 2010 note the significant crevassing which is indicative of rapid flow. The terminus is currently quickly retreating to the next peninsula where the terminus will separate into two parts. The retreat of this glacier rivals that of both Neumayer Glacier and Hindle Glacier that have also separated and opened up large new fjord reaches NASA Earth focused on this assessment. Hindle and Twitcher have both had the fastest retreat since 2015. The glacier currently has a 1 km wide calving front, but this should widen some as tributary #3 is reached. This will lead to greater retreat in terms of area if not length.

Twitcher Glacier in Landsat images from 2002 and 2015. The red arrow is the 1989 terminus and yellow arrow is the 2019 terminus. 1, 2 and 3 are tributaries.

Retreat of Twitcher Glacier in the BAS map from 1988-orange lines to 2017 green line at glacier front.

Twitcher Glacier is the next glacier south of Herz Glacier on the east coast of South Georgia. Until 1989 the glacier ended at the tip of a peninsula, the ensuing retreat has led to the opening of a new fjord. Twitcher Glacier was 10 km long and had a 2 km wide calving front in 2009. The terminus change of this tidewater glacier was completed by the British Antarctic Survey for the 1960-2007 period. The glacier retreated 1.5 km between 1960 and 2007, with have of the retreat occurring after 1992. (Gordon et al, 2008). The map below indicates the slow retreat from 1960-1988 and a more rapid retreat since. In 1989 this glacier terminated approximately at the end of a peninsula separating the two glaciers. Here we examine Landsat imagery from 1989, 2000, 2009 and 2013 to identify the rate retreat. The 1989 terminus position is indicated with a yellow arrow and the 2009 terminus position with a red arrow. The retreat is 1.2 km during this period. From 2009 to 2013 retreat accelerated with a further 1.2 km retreat to the purple arrow in the 2013 imagery, the retreat may be even greater but the resolution is poor for the January 1, 2013 image. Notice the lake just south of the glacier terminus in 1989, this lake is evident in the 2000 and 2013 imagery, but is snowcovered in 2013. A 2012 MODIS image has poorer resolution but no cloud cover and indicates the extent of the retreat from the Peninsula the glacier had reached in 1989. The last image is a closeup in Google Earth from 2010 note the significant crevassing which is indicative of rapid flow. The terminus is currently quickly retreating to the next peninsula where the terminus will separate into two parts. The southern tributary already is partly exposed to calving into the fjord. The rapid retreat here is similar to that of Neumayer Glacier or Ross Hindle Glacier.