Mountains out of molehills, a flight of fancy?

May 3rd 2018

On 13th March 2018 I was driving past Lochan Sgeireach north of Stoer (NC0328) when I noticed a large accumulation of apparently freshly dug molehills in the corner of a walled field above the road. Such was the number, in a relatively small area, that I stopped to take some photographs.

New molehills are a regular feature in late winter and early spring. It has been suggested that they may be the product of a ‘spring-cleaning’ of the burrow systems along which moles travel and in which they trap their principal prey, earthworms. Another possible cause is that surface freezing in cold winters may force some earthworms deeper, necessitating new tunnels (bit like Crossrail in London?).

Be that as it may, I began to wonder how many molehills there were at the site and roughly how much earth had been excavated to form them. Accordingly, I returned on 19th March with a shovel and container. A count revealed about 180 molehills in a triangular area about 25 x 30m (c. 375 sq.m.), in the corner of the field, with a few outliers on the edge of an old quarry outwith the wall on the south side of the field.

An average-sized hill was shovelled up and taken home to calculate its volume and weight. Its volume was about 13.5 litres and weight 12.5 kg. (if my bathroom scales are reasonably accurate!). Allowing for variations in size, compaction and dampness, a back-of-the-envelope calculation gives a total of over 2400 litres of soil shifted, with a weight in excess of two metric tonnes! Another, equally rough, calculation gives this as the earth that might be produced from digging some 1.2km of tunnel with a diameter of 5cm.

Moles have an approximate weight of 100 gms, and for my amusement I scaled this up to work out what the comparable amount of earth might be for a 90 kg man. The answer is 2025 metric tonnes, dug with the equivalent of bare hands, albeit by a creature that digs for a living! Mentioning this figure to friends, I frivolously wondered what the daily output of a miner might have been when coal was dug and moved with pick and shovel. I was referred to the Kentucky folk song Sixteen Tons, famously recorded by Tennessee Ernie Williams in 1955 (You load sixteen tons and what do you get. Another day older and deeper in debt.); it was considered, in certain circles, to be subversive!

 Ian Evans

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