November 7, 2017

Ryan Glacier, South Georgia Retreats from Tidewater

Posted by Mauri Pelto

Ryan (R) and Brunonia Glacier (B) in 1999 and 2016 Landsat images.  Red arrows indicate the 1999 terminus and pink arrows a new proglacial lake. 

Ryan Glacier and Bunonia Glacier span the width of South Georgia near its northwestern tip.  Brunonia Glacier flow east and terminates in Sunset Fjord and Ryan Glacier flows to the west into Ice Fjord, which seems more viable as a “Sunset” Fjord.  The glacier divide is a very low 400 m.  The British Antarctic Survey (BAS) has generated an excellent online map of South Georgia that includes many layers including glacier frontal change since 1958 in this region.  BAS work by Cook et al (2010) and Gordon et al (2008) have emphasized that there is a island wide pattern of calving glaciers having faster retreat.  Gordon et al., (2008) observed that larger tidewater and calving outlet glaciers generally remained in relatively advanced positions from the 1950’s until the 1980’s. After 1980 most glaciers receded; some of these retreats have been dramatic a such as Hindle and Neumayer.   Here we examine 1999-2016 Landsat imagery to identify glacier change. 

In 1999 Ryan Glacier reaches tidewater across a 1.2 km glacier front.  Brunonia Glacier terminates in Sunset Fjord pinned on what is a bedrock prominence under the ice. In 2013 and 2015 Landsat imagery from early in the melt season indicates the melt zone is below 200 m. In 2015 it is evident that Ryan Glacier no longer reaches tidewater.  In 2016 Ryan Glacier is separated from Ice Fjord by a barrier beach and a narrow developing proglacial lake, pink arrow.  The glacier has retreated 200 m since 1999.  Brunonia Glacier has experienced a 400 m retreat exposing 2 new peninsulas.  The first is on the north side of the fjord and the other is mid glacier. Both had been under the ice in 1999. The snowline in 2016 on Ryan Glacier is also higher reaching 250 m in mid-February.  Retreat of Ryan Glacier from 1958 to 1999 was 100 m, while the retreat on Brunonia in the same period was 700-800 m.

British Antarctic Survey map of frontal change 1958-2015.

Ryan and Brunonia Glacier in 2013 and 2015 Landsat images. The 2015 image indicates Ryan Glacier is no longer tidewater.