Our very own Dr Stephen Carthew, recently appraised me of an article by Elsner and Pruitt (1959) that discussed some structural and thermal characteristics of snow shelters. The article is of particular interest, because Sir Hubert is mentioned, contributing to the discussion via Koppes (1948), on the viability of constructing snow houses from unconsolidated snow using a pneumatic form (more on this shortly). Because my recent particular expertise is in snow mechanics and the use of snow as a construction material, Stephen and I thought that a contemporary appraisal of this discussion and Sir Hubert’s contribution might be of interest.
Elsner and Pruitt open their discussion with the prescient remark that increased operations into arctic regions, necessitate the need for “critical appraisal” of techniques and equipment required for operations in extreme cold; remarkably, sixty years later, post the Cold War, we are still dealing with these issues, as the race for territory and geological riches accelerates, both in the Arctic and Antarctica; see for example: https://theconversation.com/as-china-flexes-its-muscles-in-antarctica-science-is-the-best-diplomatic-tool-on-the-frozen-continent-86059 (McCallum, 2017); and, perhaps, further critical appraisal of these and similar polar-infrastructural matters, remains necessary, to enable our continued support of science in these regions: http://www.aps-polar.org/paper/2018/29/01/A180706000001 (McCallum, 2018).
The authors present their work into the construction of snow shelters from loose, unconsolidated snow (average density 0.2 gm/cm3), in the winter of 1955-56, and recognise (via numerous sources) that mechanical compaction of the snow and then “settling” is necessary, for snow of sufficient density and strength to form. This general method is termed depth processing (Taylor, 1953), a term that is still used today, where snow is firstly disaggregated (mechanically) then compacted and allowed to settle; this process is routinely practised in the construction of snow roads and runways (Abele, 1990; White and McCallum, 2018).
Abele, 1990
Abele, 1990
One phenomenon that was less well understood at the time of writing, was that snow, once disaggregated, starts to cohere or sinter together, in less than a second, as long as sufficient thermal energy exists (Szabo and Schneebeli, 2007). This process, is of course analogous, to the process that occurs in metals and ceramics, and it constrains perhaps, the last great problem in snow mechanics: how to build a compacted snow runway at the South Pole?
Such construction, remains so problematic, because there is insufficient energy for snow at an average temperature of -40oC to bond or sinter, thus strength cannot be attained, even after sufficient time and compaction, and a particulate mass of ‘swampy snow’ remains. I have two 4th year engineering students looking at this problem this year; we’ll see how they go…
Wilkins’ contribution (reported by Koppes, 1948) pertains particularly, to the construction of temporary shelters, using weather balloons. The balloon is inflated to approximately 4 feet in diameter, over which unconsolidated snow is shoveled, whereupon it is then left for at least an hour to sinter or harden. After this time, the balloon can be deflated, and the shelter finished as desired.
This process, utilising other materials such as branches etc. was not new, and had been practised by Eskimo and Indians of northern Alaska and Canada, but use of the weather balloon for such purposes, was a novel application, that the meteorologist and aviator-navigator (amongst other things), Wilkins, brought to bear, as a practical application of a simple (and robust) tool, for the emergency construction of a snow survival shelter.
One final point, that is perhaps valuable to glean from Elsner and Pruitt’s work, is the interaction between occupants of any of these shelters, and the ground. Arctic microclimates are discussed, and particularly the value that can be gained in allowing heat from the “subnivean ground surface” (subnivean: situated or occurring under the snow) to be accessed, then retained within the overarching surface snow shelter.
Conversely, Elsner and Pruitt also observe, that occupants of any of these snow shelters can still lose considerable heat by conduction through this interface. The historical use of caribou-skin sleeping pads is noted, and importantly, the need for an additional layer between sleeping bag and any ground-surface mattress is identified, to better reduce conductive heat transfer. I have personal experience of this practice from numerous mountaineering expeditions to the high Himalaya, where typically, a layer of high density foam sleeping mats are left as a foundation insulative layer in camp tents, whilst climbers carry their own air mattresses to use additionally, upon arrival at any camp.
My brief examination of this work, has revealed, that perhaps like many facets of our lives: the more things change, the more things stay the same. We continue to grapple with contested resources, around the globe, and the technical challenges that we face now, are not so dissimilar to those faced by Wilkins and his peers, in the post-Second World War, and Cold War periods.
As Wilkins aficionados, we can revel in the diversity of skills that Wilkins acquired, and the many and varied environments in which he was able to utilise his knowledge, for the benefit of others. Perhaps at this time in particular, a re-examination of our own skills, and the benefits that might be reaped by others, upon application, should be considered…
References
Abele, G., 1990. Snow Roads and Runways, Monograph 90–3, Cold Regions Research and Engineering Laboratory, US Army Corps of Engineers, Hanover, New Hampshire, USA.
Elsner, R. W. and Pruitt, Jr., W. O., 1959. Some Structural and Thermal Characteristics of Snow Shelters, Arctic, Vol. 12, No. 1 (Mar., 1959), pp. 20-27.
Koppes, W. F., 1948. A report on characteristics of snow houses and their practicality as a form of temporary shelter. A report to the subcommittee on shelter and clothing, Committee on Sanitary Engineering and Environment, National Res. Council, Washington.
McCallum, A. B., 2018. Polar science needs a foundation: where is the research into Polar infrastructure? Advances in Polar Science, Vol. 29, Issue 1, pp. 1-2.
McCallum, A. B., 2017. Keep it cool: how science is the best diplomatic tool in Antarctic, The Conversation.
Szabo, D. and Schneebeli, M., 2007. Subsecond sintering of ice. Applied Physics Letters. Vol 90.
Taylor, A., 1953. Snow Compaction. SIPRE Rep. 13. Snow, Ice and Permafrost Res. Est., Corps of Eng., U. S. Army, Wilmette.
White, G. and McCallum, A. B., 2018. Review of ice and snow runway pavements, International Journal of Pavement Research and Technology, Vol. 11, Issue 3, pp. 311-320.