Fiftyone Glacier is a large glacier flowing southwards, on the south side of Heard Island in the southern Indian Ocean. Its terminus is located between Lavett Bluff and Lambeth Bluff. To the northeast of Fiftyone Glacier is Winston Glacier, whose terminus is located at Winston Lagoon, between Cape Lockyer and Oatt Rocks. To the west of Fiftyone Glacier is Deacock Glacier, whose terminus is located between Cape Labuan and Long Beach.
Fiftyone Glacier was surveyed by ANARE (Australian National Antarctic Research Expeditions) in 1948. It was named "The 1951 Glacier" by an ANARE party that made a traverse of Heard Island in 1951. The form Fiftyone Glacier was recommended by Antarctic Names Committee of Australia (ANCA) in 1964.
The landscape of Heard Island and nearby McDonald Island is constantly changing due to volcanism, strong winds and waves, and climate change. Volcanic activity has been observed in this area since the mid-1980s, with fresh lava flows on the southwest flanks of Heard Island. Satellite imagery shows that McDonald Island increased in size from about 1 to 2.5 square kilometers between 1994 and 2004, as a result of volcanic activity.
In addition to new land being produced by volcanism, warming of the climate is causing the retreat of glaciers (see below section). These combined processes produce new ice-free terrestrial and freshwater ecoregions such as moraines and lagoons, which are now available for colonization by plants and animals. Heard Island has vast colonies of penguins and petrels, and large harems of land-based marine predators such as elephant seals and fur seals. Due to the very high numbers of seabirds and marine mammals on Heard Island, the area is considered a "biological hot spot". The marine environment surrounding the islands features diverse and distinctive benthic habitats that support a range of species including corals, sponges, barnacles and echinoderms. This marine environment also serves as a nursery area for a range of fishes, including some species of commercial interest.
Heard Island is a heavily glacierized, subantarctic volcanic island located in the Southern Ocean, roughly 4000 kilometers southwest of Australia. 80% of the island is covered in ice, with glaciers descending from 2400 meters to sea level. Due to the steep topography of Heard Island, most of its glaciers are relatively thin (averaging only about 55 meters in depth). The presence of glaciers on Heard Island provides an excellent opportunity to measure the rate of glacial retreat as an indicator of climate change.
Available records show no apparent change in glacier mass balance between 1874 and 1929. Between 1949 and 1954, marked changes were observed to have occurred in the ice formations above 5000 feet on the southwestern slopes of Big Ben, possibly as a result of volcanic activity. By 1963, major recession was obvious below 2000 feet on almost all glaciers, and minor recession was evident as high as 5000 feet.
The coastal ice cliffs of Brown and Stephenson Glaciers, which in 1954 were over 50 feet high, had disappeared by 1963 when the glaciers terminated as much as 100 yards inland. Baudissin Glacier on the north coast, and Vahsel Glacier on the west coast have lost at least 100 and 200 vertical feet of ice, respectively. Winston Glacier, which retreated approximately one mile between 1947 and 1963, appears to be a very sensitive indicator of glacier change on the island. The young moraines flanking Winston Lagoon show that Winston Glacier has lost at least 300 vertical feet of ice within a recent time period. Jacka Glacier on the east coast of Laurens Peninsula has also demonstrated marked recession since 1955.
Retreat of glacier fronts across Heard Island is evident when comparing aerial photographs taken in December 1947 with those taken on a return visit in early 1980. Retreat of Heard Island glaciers is most dramatic on the eastern section of the island, where the termini of former tidewater glaciers are now located inland. Glaciers on the northern and western coasts have narrowed significantly, while the area of glaciers and ice caps on Laurens Peninsula have shrunk by 30% - 65%.
During the time period between 1947 and 1988, the total area of Heard Island's glaciers decreased by 11%, from 288 km2 (roughly 79% of the total area of Heard Island) to only 257 km2. A visit to the island in the spring of 2000 found that the Stephenson, Brown and Baudissin glaciers, among others, had retreated even further. The terminus of Brown Glacier has retreated approximately 1.1 kilometres since 1950. The total ice-covered area of Brown Glacier is estimated to have decreased by roughly 29% between 1947 and 2004. This degree of loss of glacier mass is consistent with the measured increase in temperature of +0.9 °C over that time span.
Possible causes of glacier recession on Heard Island include:
- Volcanic activity
- Southward movement of the Antarctic Convergence: such a movement conceivably might cause glacier retreat through a rise in sea and air temperatures
- Climatic change
The Australian Antarctic Division conducted an expedition to Heard Island during the austral summer of 2003-04. A small team of scientists spent two months on the island, conducting studies on avian and terrestrial biology and glaciology. Glaciologists conducted further research on the Brown Glacier, in an effort to determine whether glacial retreat is rapid or punctuated. Using a portable echo sounder, the team took measurements of the volume of the glacier. Monitoring of climatic conditions continued, with an emphasis on the impact of Foehn winds on glacier mass balance. Based on the findings of that expedition, the rate of loss of glacier ice on Heard Island appears to be accelerating. Between 2000 and 2003, repeat GPS surface surveys revealed that the rate of loss of ice in both the ablation zone and the accumulation zone of Brown Glacier was more than double average rate measured from 1947 to 2003. The increase in the rate of ice loss suggests that the glaciers of Heard Island are reacting to ongoing climate change, rather than approaching dynamic equilibrium. The retreat of Heard Island's glaciers is expected to continue for the foreseeable future.