Anne McConnell

Geomorphology of the Sub-Antarctic Australian Territory of Heard Island-McDonald Island

The geomorphology of Heard Island-McDonald Island is primarily the product of close interplay between volcanism, glaciation, and vigorous marine processes in a stormy sub-Antarctic environment. The dominant landform is the strato-volcano Big Ben (2745m), which is the highest mountain on Australian territory outside Antarctica. Other volcanic landforms include scoria cones, domes, open vertical volcanic conduits, lava flows and lava tubes. Volcanic activity is ongoing from the summit of Big Ben, and from Samarang Hill on McDonald Island. Early, but unproven, glacial sediments may exist within the Late Miocene - Early Pliocene Drygalski Formation, which forms a 300m high plateau along the northern coast of Heard Island. Growth of the present glaciers, some of which reach sea level, has been a response to progressive growth of the volcanoes. A variety of erosional and depositional glacial landforms is present, including major lateral moraines and extensive hummocky moraines. Vigorous longshore drift and an abundant sediment supply have produced a large spit at the downdrift end of the island, and formed bars from reworked glacigenic sediment that now impound proglacial estuarine lagoons, some of which have grown rapidly over recent decades as tidewater glaciers have retreated. Integrated study of the volcanic, glacial and coastal sequences offers the possibility of constructing a well-dated record of climate change. Research into the geomorphology, surficial sediments, and contemporary geomorphological processes, including glaciofluvial sediment flux, is also important as an aid to environmental management on land, and to management of the adjacent marine environment.

Deglaciation and weathering of Larsemann Hills, East Antarctica

Abstract In situ cosmogenic 10Be exposure dating, radiocarbon determinations, salt and sediment geochemistry, and rock weathering observations indicate that parts of Larsemann Hills, East Antarctica have been subaerially exposed throughout much of the last glacial cycle, with the last glaciation occurring prior to 100 ka bp. Salt-enhanced subaerial weathering, coupled with a paucity of glacial erratics, made exposure age dating challenging. Rapid subaerial surface lowering in some places means that some exposure ages may underestimate the true age of deglaciation. Despite this uncertainty, the data are consistent with the absence of overriding by a thick ice sheet during the Last Glacial Maximum ∼20–18 ka bp.

Late Pliocene age of glacial deposits at Heidemann Valley, East Antarctica: evidence for the last major glaciation in the Vestfold Hills.

Abstract A Pliocene (2.6–3.5 Ma) age is determined from glacial sediments studied in a 20 m long, 4 m deep trench excavated in Heidemann Valley, Vestfold Hills, East Antarctica. The age determination is based on a combined study of amino acid racemization, diatoms, foraminifera, and magnetic polarity, and supports earlier estimates of the age of the sedimentary section; all are beyond 14C range. Four till units are recognized and documented, and 16 subunits are identified. All are ascribed to deposition during a Late Pliocene glaciation that was probably the last time the entire Vestfold Hills was covered by an enlarged East Antarctic Ice Sheet (EAIS). Evidence for other more recent glacial events of the ‘Vestfold Glaciation’ may have been due to lateral expansion of the Sørsdal Glacier and limited expansion of the icesheet margin during the Last Glacial Maximum rather than a major expansion of the EAIS. The deposit appears to correlate with a marine deposition event recorded in Ocean Drilling Program Site 1166 in Prydz Bay, possibly with the Bardin Bluffs Formation of the Prince Charles Mountains and with part of the time represented in the ANDRILL AND-1B core in the Ross Sea.

Glacier retreat and melt-lake expansion at Stephenson Glacier, Heard Island World Heritage Area

Historical records, recent observations, and geomorphological evidence indicate that rates of retreat and downwasting of the tidewater Stephenson Glacier, and concurrent expansion of ice-marginal melt-lakes, has increased by an order of magnitude since 1987. Melt-lake expansion is partly the product of greatly accelerated ablation of older, ice-cored twentieth-century moraines. The timing of these changes broadly coincides with reported increases in atmospheric and sea-surface temperatures around other sub-Antarctic islands, but correlates less well with changes along the northern Antarctic Peninsula, where warming has been more rapid. These recent changes in landscape character and geomorphological processes have implications for geodiversity, biodiversity, and cultural heritage values in this World Heritage Area. Ifthe causal climatic warming is anthropogenic, it reinforces the fact that even the most remote and littlevisited nature conservation reserves may be compromised by off-site human impacts, confronting management authorities with difficult philosophical and practical issues.

Impacts of geoscience research on the physical environment of the Vestfold Hills, Antarctica

Antarctic polar deserts can be of considerable scientific interest, but can also exhibit great environmental sensitivity. A variety of factors, including Australias legal obligations under the Madrid Protocol, public expectations, certain research opportunities and ethical considerations, demand a very high standard of environmental protection. A survey outside the Davis Station limits in the Vestfold Hills, East Antarctica, identified 66 sites at which past human activities had left long term impacts on the physical environment. Nearly half of all observed impacts were the result of geoscientific research that had left old pit and trench sites, vehicular tracks, partly excavated palaeontological material, rock sampling and drilling sites, localised slope instability caused by disturbance, and discarded equipment and markers. Comparisons between rehabilitated sites and others where little, if any, rehabilitation appears to have been attempted suggest natural processes alone are generally insufficient to heal the damage, but that effective rehabilitation is often possible if undertaken immediately after the initial disturbance.