Rudolf (Part II): The Overlooked Glacier

The Overlooked Glacier

Rudolf Glacier is a small valley glacier that lies in a private valley wedged between New Zealand’s most expansive ice-masses and towering summits. As one of the lesser entities in the region, glaciological researchers have largely neglected it, relegating it to the footnotes, as they explore its grander brethren. As the second largest tributary glacier (Hochstetter Glacier being the first) feeding into the gargantuan Tasman, the nation’s most expansive glacier, it is somewhat surprising that no teams have directed their expeditions across Rudolf.

The Rudolf-Tasman Region. Annotated satellite image from Bing Aerial Maps.

Considering Rudolf’s intimate relationship with the Tasman, the most extensively studied glacier in New Zealand, I was interested to determine what had held back research on the former. In several publications the dearth of comprehensive investigations of smaller glaciers has been attributed to insufficient funding. My first speculation was that Rudolf had not been prioritised due to its smaller size. However, investigations have been carried out on far smaller masses. For example, the Brewster Glacier, 95km southwest of Rudolf, which is a mere 2.5km2. The 2010 study examining the more southerly cirque glacier was embarked upon in efforts to quantify the responsiveness and potential runoff contributions of smaller glaciers under changing climates. Of New Zealand’s 3144 individual glaciers, according to Dr Chinn c. 2001, 28.8% or 905 of them cover between 0.04-0.08km2. In fact, whilst Rudolf is relatively small at the global scale, it is actually amongst the 30 largest individual glaciers over 5.12km2.

My personal interpretation of Rudolf’s absence from the literature is that it has slipped through a gap. Its residence in a somewhat remote region, hemmed in by a far more impressive mass, combined with its limited capability to directly impact humanity has kept it off the radar. However, I propose that it is its ‘Goldilocks’ status, being neither excessively large nor diminutive, which has resulted in its being less microcosmic or representative of the generalised conditions across the island nation, and thus decreased its perceived value as a subject of study.

Despite this rejection, the Rudolf Glacier still provides some interesting insights into glacial conditions in New Zealand, outside of the more mainstream and prolific investigations of Franz Josef, Fox, Tasman, Hooker and so on.

 

An Aerial Perspective

The Rudolf Glacier has remained poorly delineated since its identification in the late 19th Century. Longitudinally, it may extend as many as 10.5km, but its trunk can only be satisfactorily confirmed up to ~8.7km. Areally, it is suspected to cover around 6km2. It tumbles from cirques on the slopes of Mounts Jervois and De la Beche, skirts the base of Mount Tasman, and flows into the main valley, vying with the heavyweight Tasman Glacier. Rudolf is subsequently heavily compressed and/or subducted, as it is channelled between (or under) the larger ice-mass and fellow tributaries and the valley sides. Attempts to definitively identify its outline have thus far been thwarted by the mass of dark deposits strewn across its surface, a common complication in New Zealand’s glacier studies, and remotely sensed glaciological studies in general.

The layer of overlaying alluvium is comprised of a hard sedimentary rock called ‘argillite’. It covers the majority of the lower Rudolf, from its terminus through to ~1900 metres above sea level (masl). The debris cover, which is dark and directly in contact with the ice, is sometimes misinterpreted as contributing to the ice’s decay, as it decreases the surface albedo and absorbs incoming solar radiation. In many instances, this is true, however, it is dependant on the thickness of the supraglacial layer (which sits atop the glacier). In fact, it often acts as a protective blanket, insulating the glacier from external temperature fluctuations.

In 2010, Natalya Reznichenko and her team explored the insulative effects of different debris cover depths. They determined that there is a direct relationship between greater thickness and lowered melting rates. Under laboratory conditions they found that 13cm of debris acted as a shield, preventing ice from melting for over 12 hours of direct exposure to radiation. Studies by Dr Trevor Chinn empirically verified the assertions in the field, demonstrating that debris cover has severely dampened climatic forcings upon Tasman and its neighbours. He determined that ‘debris blankets’ of up to 200cm overlaying glacier termini had reduced melting rates by 90%, in spite of relatively high temperatures at the valley floor. This has resulted in sections of regional glaciers experiencing a reprieve from the immediate effects of climate change, endowing them with prolonged lags. Glacier sensitivities are also highly predicated upon size, surficial and subglacial angle, and contact with water bodies. Overall, general patterns have been observed, with small cirque and alpine glaciers responding within one to two decades, and valley glaciers reacting in 10-50 years. Tasman, the most massive glacier, reacts at the centennial scale. In defiance of these trends, the clean and relatively steep leviathans Franz Josef and Fox Glaciers exhibit lagged effects within 5-8 years. This disparity has been a subject of considerable fascination, particularly for academics of the Mt Cook/Aoraki region.

[to be continued]

 

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