Down by Kosciuszko

Being a hot, dry, flat continent, Australia is not known for its glaciation. The ice ages are marked by the expansion and contraction of ice and the presence of glaciers in high mountains worldwide. Every 100 thousand years or so huge sheets of ice several kilometres thick advanced over Europe and North America and then melted away. Although Australian glaciation was not so dramatic, the action of glaciers together with frost, ice and snow were important agents of landscape change in the mountains of southeastern Australia and Tasmania.

The only part of the Australian mainland to be glaciated was the Kosciuszko massif of the Snowy Mountains. Outside of palaeontological studies, this is the longest studied ice age site in Australia. During a field trip in 1851-52, Reverend W B Clarke, one of the founders of Australian geology, was the first to identify glacial landforms. Fixated on gold exploration, he speculated that there may exist gold moraines where the precious metal was concentrated by the glacier and meltwater, as occurred at Kumara in New Zealand. In 1885 polymath Robert von Lendenfeld wrote the first descriptive paper with observations of glacial erosion. He provided the first, if somewhat imaginative, glacier reconstruction for the valley behind Mt Kosciuszko, when it was known as Mt Townsend. Without dating, he concluded based on weathering that the glaciation was recent and synchronous with New Zealand at a time when the rivers were very large and the megafauna still existed. Shortly after, Richard Helms in 1893 extended the observations and proposed the entire massif was glaciated to below 1600 m with glaciers even dry calving into the Thredbo valley.

The glaciation of Australia then drew the interest of another famous Australian geologist, Sir Edgeworth David. David grew up in Wales and wrote about glaciation around Cardiff. In 1901 David led a paper describing glaciation along the Main Range, with a beautifully illustrated map of the main glacial landforms and topography. David came up with an ingenious method for determining the date of the glaciation. He noticed that 10 feet of phyllite had been eroded beside a moraine and that since similar rocks in Victoria were eroding at 1 inch/100 years, he calculated the ice age ended 12,000 years ago. This is the first age estimate in Australian Quaternary geology. This calculation came almost 50 years before radiocarbon dating (radioactivity had only just been discovered leading to a radical revision of the age of the Earth). The age was only improved upon some 70 years later by Alec Costin, who radiocarbon dated peats near Blue Lake. At the turn of the century, Geologists in North America were also trying to date the end of the ice age. Using the retreat of Niagara Falls, Charles Lyell, founder of modern geology, estimated 35,000 years. Lastly, David estimated that cooling of 3.4-4.4 °C would be needed to lower the snowline some 700-800 m, the first palaeo-temperature estimate in Australia.

David noted that the only indisputable evidence of glaciation could be traced down to 1770 m, the moraines below Blue Lake. However, beyond this there was ambiguous evidence that that was suggestive of glaciation. If ever glaciated, it must of been of considerable antiquity because of the amount of erosion that had taken place since. He warned: “With regard to the general evidence of a possible extensive glaciation along the whole Kosciusko Plateau as far down as Boggy Plains…great caution should, in our opinion, be exercised in interpreting the phenomena“.  David followed with another paper in 1908 and abandoned this caution. He explained away the differential weathering as being because of protection by snow (now known to be clearly wrong) and made the critical mistake of relying only on meso-scale landforms such as valley shape to map glaciation. He proposed a 3-phase glacial model which pre-dated the Alpine 4-phase model proposed by Penck and Brückner in 1909. David guessed the first phase may have been 200,000 years ago. He dated the middle phase of glaciation to 50,000-100,000 years based on down-cutting of the Snowy River and maintained his estimate of 10,000-20,000 years ago for the cirque glaciation. The maximum area of glaciation over the plateau he estimated was at least 210-260 km².

By 1925, Kosciuszko had attracted the attention of yet another well known geographer and a geologist, T. Griffith Taylor and a young W. R. Browne, who made the first topographic map of the massif and mapped further glacial features. This work began a lifelong fascination with the glaciation of Kosciuszko for Browne. From 1944 onwards Browne and colleagues added observations to those of David’s 3-phase model and expanded possible glacial explanations for landforms all over the Snowy Mountains. He estimated that ice reached down to 1430 m and covered more than a whopping 1040 km² as an ice cap. However, Browne failed to realise the equifinality of the granitic landscape. Erosion over long periods of time can produce rounded boulders reminiscent of glacial erosion and broad valleys resembling U-shaped valleys and cirques.

In 1963 a Scottish geomorphologist, Bob Galloway, published a paper that dramatically revised the extent of glaciation. Having trained in Scotland and seen much of its granitic glaciated terrain from the air when he trained as an army pilot, Bob was much more familiar with actual glacial landforms. He estimated that even taking into account marginal evidence, no more than about 50 km² was glaciated. In a brilliantly carefully reasoned argument, he disassembled the 3-phase model expounded by Browne like a game of geomorphological Jenga. Browne was not impressed and attempted to get Bob’s paper retracted from the Proceedings of the Linnean Society of New South Wales. The paper was upheld and in a final show of poor scientific form, Browne refused to cite it in his final papers.

I was introduced to Kosciuszko in a first year geology trip at the Australian National University, where we visited Blue lake and measured slope angles on a blockslope at Mt Guthrie. I was fascinated by Bob’s papers and saw a pressing need to place ages on the glacial landforms. So when it came time to pick a PhD topic I approached John Stone, who had recently introduced the new technique of exposure dating to Australia. I proposed to date the best preserved moraines at Blue Lake and Lake Cootapatamba. The 3D model above is made from the aerial photos I used to map the glacial limits. I found no more than 15 km² was definitely glaciated¹. I avoided speculative landforms beyond these limits because my thesis focused only on the last glacial maximum. More recently I have revisited the area with Jaap van der Meer (a Dutch till expert) in 2009 and Stephanie Mills (a cirque glacial expert) in 2012. On these occasions we found evidence for an older glaciation in the form of till, striations and erratics outside the limits I mapped, possibly doubling the area in the Snowy River Valley.

The results of the exposure dating surprised everybody. There was not one phase of glaciation, as suggested by Bob, but 3 preserved in the moraines at Blue Lake. The first ice formed some 60,000 years ago, the second 32,000 years ago and then there were 2 limits in the last phase during the last glacial maximum, about 20,000 years ago. It seemed fittingly close that the youngest limit was so similar to that of the original age estimate made exactly 100 years ago from the date of publication. We had gone full circle.

1. Barrows, T.T., Stone, J.O., Fifield, L.K., Cresswell, R.G., 2001. Late Pleistocene Glaciation of the Kosciuszko Massif, Snowy Mountains, Australia. Quaternary Research, 55(2), 179-189.

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