Rain & the igloo

We have experienced days of heavy rain and warm weather. I do not know how the igloo fared during this time. So, I am awaiting a report from anyone who visits the igloo site. There is some sun today, and the temperature has dropped a bit. Click Continue for more.

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We built the igloo just above the snowline in Cypress Bowl. The object of the day was to make an igloo – not create a semi-permanent shelter. Easy access to a suitable site was a more important issue than finding a location that would ensure its longevity. Last week’s blog entry called Time to build an igloo! has maps to the site.

Nevertheless, after it was up, some folks were planning overnight trips to the igloo; so it would be nice if it survived the rains.

I was asked if the catenary profile of the igloo would allow it to maintain its strength even when drenched with rain. I don’t know, but I think the answer to that depends on the way a snow structure maintains its integrity.

By handling the snow, and packing it into the form, we were work-hardening the snow. That means the process caused the snow crystals to sinter, or freeze together. The magic, then, is observing how work-hardened snow transforms itself. When we stamp on snow it may be crumbly when we stop stamping, but an hour later it is hard. When we position the little red plastic ball-joint that marks the center of the igloo, and attaches to the rod that guides the Icebox as we make the igloo, we have to be very careful not to jiggle it because it is secured only by soft snow. At the end of the day I usually have to chop with my steel avy shovel to dig it out.

If the weather is cold, a few hours after the igloo is complete I can stand on the top and it will support me. (The manufacturer does not recommend doing this!) The structure of the igloo is maintained because the crystals have frozen (sintered) together. Since the structure has become a solid form, the weight of the igloo is distributed down the walls by the catenary shape.

I suspect this changes when it rains. We learned from our avalanche training that when it rains on snow, the water, percolating down through the snow, melts the connections between the crystals. This gives rise to those low-angle wet-snow avalanches on sun-warmed slopes in the spring. Rain must also add to the weight of the igloo. If this happens, I think it is possible for gravity to pull the upper part of the igloo straight down, and the roof of the igloo could collapse.

Following this line of reasoning, if the temperature drops before the igloo collapses, it would quickly re-freeze, probably making the igloo stronger than ever.

Looking up at the hills, I can see lots of new snow frozen on trees above 4000 feet. The attitude of the igloo is about 3000 feet — so it may be high enough. Is that just wishful thinking?


2 Responses to “Rain & the igloo”

  1. 1 snowfortbuilder August 3, 2007 at 9:01 am

    igloos and quinzhees are usually pretty strong depending upon the the width of the walls. I have stood on top of my quinzhee but the walls were all at least a foot thick.

  2. 2 Robert August 3, 2007 at 10:22 am

    @SF-builder, thanks for dropping by. These igloos, built with the Grand Shelters Icebox are very strong… after the dome has hardened, and if the weather is cold. The wall is 8-inches thick. The system produces a catenary dome, which is a stronger shape than a hemisphere. If the temperature rises above freezing (which it often does around here in the winter) the igloo becomes soft. Instead of collapsing, it seems to slowly deflate. When it is soft, trying to load it with the weight of a person would not be a good idea.

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