Two Hundred Thousand Tonnes of snow.
27th March 2019
It was mild and damp in Lochaber today. The snowpack is thawing at all levels. I borrowed a snow density measurement device from a colleague and measured the density of the tops three layer of the snowpack when I did my snowpit. The results were 450kg/m3, 330 kg/m3 and 470kg/m3 respectively.
How much snow is there on the hills? This was something I was pondering on the way down, and decided to do a rough calculation. Instead of snow on the hills in general, I decided to consider a location that I know quite well, and is also good at collecting snow. This is Coire an Lochan on Aonach Mor. I estimated the area of the coire by counting up the 100 by 100 metres ming grid square on the map (see 3rd picture down). This gave 42 squares which gives a total area of around 420000 square metres. To make the numbers easier I rounded this down to 400000 square metres.
The snow density I measured today was near the surface of the snow pack. I made the assumption that the average snow density is bit higher than this as the snow deeper in the snowpack will be older, and have had more time to settled and get denser. I assumed an average snow density of around 500 kg/m3. Now the final assumption I had to make is the average depth of the snow in the coire. This is the assumption that I would say has the greatest uncertainty associated with it. The actual depth will be very variable, from zero to in some places 4 or more meters in other places. I assumed an average depth of 1 metre.
Multiplying 400000 by 500 by 1 and then dividing by 1000 (to change the units from kg to metric tonnes) gives a total snow mass of the order of 200000 tonnes of snow. Although the value of two hundred thousand tonnes of snow might be a bit high (I am slightly dubious of my assumption of an average snow depth of 1m), there is certainly a fair mass of snow up there.
Given that this winter has been a very low snow year, think how much snow there must be in the Coire at the end of a snowy winter. The short answer would be, a lot!
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