Submarine geology and geomorphology of active sub-Antarctic volcanoes: Heard and McDonald islands

Monday, 30 January 2017
Marina/Gretel (Hobart Function and Conference Centre)
Sally Joan Watson1, Millard F Coffin2, Joanne M Whittaker3, Vanessa Lucieer1, Jodi M Fox3, Rebecca Carey4, Richard J Arculus5, Andrew R Bowie3, Zanna Chase6, Robin Robertson7, Tara Martin8, Frances Cooke8 and HEOBI IN2016_V01 Shipboard Party, (1)University of Tasmania, Institute for Marine and Antarctic Studies, Hobart, Australia, (2)University of Tasmania, Hobart, TAS, Australia, (3)University of Tasmania, Hobart, Australia, (4)University of Tasmania, Earth Sciences, Hobart, TAS, Australia, (5)Australian National University, Canberra, Australia, (6)University of Tasmania, Institute for Marine and Antarctic Studies, Hobart, TAS, Australia, (7)UNSW at AFDA, Canberra, Australia, (8)CSIRO Marine and Atmospheric Research Hobart, Hobart, Australia
Abstract:
Heard and McDonald islands (HIMI), Southern Ocean, are active World Heritage listed sub-Antarctic volcanic islands. HIMI represent subaerial exposures of the second largest submarine Large Igneous Province globally – the Kerguelen Plateau. The formation of the Kerguelen Plateau began ~120 Ma, amidst the breakup of East Gondwana. Located on the Antarctic plate, the Kerguelen Plateau remains volcanically active in the HIMI region today.

Onshore, processes influencing island evolution include glaciation, weathering, volcanism, tectonics and mass-wasting (Duncan et al. 2016). Waters around HIMI are largely uncharted due to their remote location. Hence, the extent to which these processes manifest in the submarine environment around HIMI has not been investigated.

In early 2016, we conducted marine geophysical and geological surveys around HIMI aboard RV Investigator (IN2016_V01). Results show that volcanic and sedimentary features trend east-west, likely a result of erosion and deposition by the eastward flowing Antarctic Circumpolar Current and tidal currents.

Spatial patterns of submarine volcanism and sediment distribution differ substantially between the islands. New data reveal 3 sea knolls north of Heard Island and >70 sea knolls around McDonald Islands suggesting substantial submarine volcanism. Geophysical data indicate hard volcanic seafloor around the McDonald Islands, whereas the seafloor near Heard Island is characterised by sedimentary sequences tens of meters or more thick and iceberg scours - indicative of glacial processes.

Differences in submarine geomorphology are likely due to the current glaciation of Heard Island, differing rock types (Heard: alkali basalt; McDonald: phonolite), and dominant eruptive products (clastics vs. lava). Variations may reflect different magmatic plumbing systems beneath the two active volcanoes; Heard produces larger volumes of more focused lava, whilst McDonald extrudes smaller volumes of more evolved lavas from multiple vents across the edifice.

Our results reveal for the first time the extent and nature of submarine volcanism in the vicinity of HIMI. Using geophysical data corroborated with new and existing geologic data, we present the first geomorphic map of HIMI, detailing the processes that build and shape the submarine environment.

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