Australia: The Land Where Time Began

A biography of the Australian continent 

Antarctica - Glacier Tongues

Glacier tongues are individual glacial outlet systems at the coast that can extend out into the sea where they have a significant role in draining ice and delivering sediment to the ocean, in spite of their relatively small area (Drewry & Cooper, 1981). Characteristics of all glacial tongues are having portions that are confined in coastal valleys and buoyant regions in open marine environments. In Antarctica glacier tongues are among the most dynamic glacial features, undergoing radical size and shape changes within a few years, with average ice drainage velocities of typically more than 0.5 km/yr, and the velocities can reach up to 3.7 km/yr (Lindstrom & Tyler, 1984; McDonald et al., 1989).

The largest ice tongue in the Ross Sea, at 70 km long by 20 km wide, is the Drygalski Ice Tongue, the seaward extension of David Glacier that has a drainage basin area of 240,000 km² (Swithinbank, 1988). The Drygalski Ice Tongue has advanced seawards, as shown by satellite imagery, at a velocity ranging from 136-912 ± 30 m/yr over the past few decades Frezzotti, 1992). The Erebus Glacier Tongue, also in the Ross Sea, underwent a major episode of calving in the early 1940s, though since then it has advanced seaward (Keys, 1990).

According to the author¹ the most unstable part of the WAIS is believed by some to be the Pine Island Bay glacial system (Hughes, pers. comm. to the author¹) as in Pine Island Bay the floating terminus of the ice sheet is unstable. Between 1961 and 1969 the length of the Thwaites Glacier Tongue In Pine Island Bay doubled in length before breaking off in a series of episodes of calving that left the glacier snout close to the coast, and since 1972 it has been growing in a seawards direction at a rate that has reached up to 3.7 km/yr (Lindstrom & Tyler, 1984). Basal melting is currently [1999] occurring at up to 10-12 m/yr on the nearby Pine Island Glacier and it glacier tongue, as relatively warm water has been impinging onto the shelf beneath them (Jacobs et al., 1996).

The combined area that is drained by the Mertz and Ninnis Glacier tongues, in East Antarctica, on the coast of Wilkes Land, more than 400,000 km². The glacier tongues were named after members of Douglas Mawson's coastal research team who died during the expedition in 1914. The size and shape of the glacier tongues were significantly different from the maps compiled by the Soviet Antarctic Expedition in 1958 and the Deep Freeze Expedition in 1979 (Domack & Anderson, 1983). Between 1914 and 1958 both glacier tongues had retreated to near the coastline, and by 1979 they had advanced seawards by 10s of kilometres (Domack & Anderson, 1983).

Sources & Further reading

1. Anderson, John B., 1999, Antarctic Marine Geology, Cambridge University Press