How much energy is needed to melt a cubic metre of snow?
I tried googling the question, naively thinking a simple answer would be out there, and reckoned the figure would be surprisingly large. But I had no idea that the subject would be so complex.
To change the physical state of ice into water, or indeed water into steam, requires a relatively huge amount of energy. This enthalpy of fusion (or latent heat of fusion, as I remember it being called) is 333.5 Kilo Joules for 1 kg of ice, just to get it to melt, let alone become warmer than 0 degrees C. To put this into context, this is almost exactly the same amount of energy which would be required to heat the water by a further 80 degrees C.
So when a landscape is covered in about a foot of snow, as it was here, a huge amount of energy is going to be needed to melt all that snow. I wonder how many folk in Erie, Pennsylvania are contemplating this issue right now, after the city on the shores of the Great Lakes had a record snowfall on Christmas day and Boxing day of more than 4 feet of snow in just 30 hours. Click here for more and a great video of what that amount of snow looks like…
Even with our now cosy house, we always notice how the energy is silently drained from the physical structure of the building whilst we have melting snow or ice on the roof and surrounding land – at least until it’s all melted. It typically takes 2 or 3 days after the snow has all gone for the house to reach a cosy equilibrium again. Much of the stored energy in the physical structure and contents of the house (its core temperature, if you like) is clearly being sucked into changing the physical state of the fallen snow on the roof from ice to water.
However, back to the issue of the total energy required to melt all this snow. I found a fascinating paper on the subject.Click here for more. But be warned, there are an awful lot of equations involved. Interestingly it originates from Colorado, where I guess issues of snow melt are a regular annual, significant event, rather than the more occasional novelty here.
The paper’s introduction explains that for any accumulation of snow to melt, 3 phases of the process can be considered to take place.
Firstly the snow pack has to warm so that it is isothermal at 0 degrees C – i.e. the temperature of the snow needs to rise from below freezing to zero. This is known as the warming phase of snow melt.
Secondly the snow pack starts to melt, but water from the melting snow is retained within the snow in the tiny air spaces which are present, as a result of surface tension. This phase is known as snow ripening.
This is a very simplified guide to a complex process which is controlled by the net energy influx into the snow. This total net energy figure is the sum of many different and variable components…
- Net short wave radiation – the “net” reflecting the fact that such radiation moves both into, and out of the snow pack, but is usually a net positive figure, affected by such parameters as sunshine, cloud cover, forestation, or slope of the ground.
- Net long wave radiation – again there will be energy movements both into and out of the snow in the long wave spectrum, though this figure is usually negative – i.e. more long wave energy is lost, than gained. Cloud and tree cover affect this significantly, trees will act like black bodies radiating energy downwards…
- Turbulent sensible heat flux – through diffusion there will be temperature gradients within the snow pack and that of the overlying atmosphere.
- Turbulent latent heat flux – again the heat changes from the ice undergoing a change in physical state and melting to water within the snow pack will create movements of energy within the snow.
- Heat input from rain. This can be the single biggest factor in supplying the energy necessary to melt snow, at least in our part of the world, particularly around the shortest day when the sun’s input energy is quite weak, and daylight hours so short. But even this can be complex – if the snow is at zero degrees C already then the rain cools to freezing and this energy is use to melt the snow. If however the snow is still well below freezing, then when the rain falls, the rain will first freeze – but in doing so will release the latent heat of freezing which can be a very valuable extra energy input in warming up the rest of the snow pack!
- Conductive exchange of heat with the ground. Heat usually transfers up into the snow pack from the ground below, assuming the ground isn’t colder than the snow which has fallen. But how quickly depends on temperature gradients, and also how good a conductor the ground is. So wooden steps, solid stone, or crushed slates of chippings all have different heat conductivity.
Maybe the images above will help to illustrate some of these factors. It also gives the detailed background to the complexities of the spiral conundrum, which has intrigued me and a few readers over the years.
Click here, here and here (particularly the comments) for more on this phenomenon. This year, all melt events seem to have fallen into the “quarry tiles first” group, rather than the now rarer “crushed slates first” group, which is what I evidently appeared to think was the “normal” mode back in 2012…
If such consideration of physics is all a bit too involved, sincere apologies. Perhaps alternatively just consider some simple words and images of snow…
And I propose a new word – Melze. A verb – To describe the rare effect witnessed this last week when very heavy wet snowflakes fell at night, lingered, began to melt on the ground, and then as skies cleared and temperatures fell further, refroze, creating seaweed like fronds of ice over much of the garden by morning. Quite different to the familiar rigid icicles formed by a similar melt/refreeze along our roof drip line.
Along with the forty five snowdrop varieties which are already “out” or “open” by the turn of the year here, the unsung stars of the winter garden, our Cyclamen coum have been just as delightful. Every year they get better, and this year I’ve had a burst of energy digging up seedling tubers to pot on.
With new areas of the Lower meadow copse available for planting up, they’re a perfect option, and although I’ve tried planting some directly in situ, the inevitable raking of the surface by blackbirds can disturb such tiny fragile tubers, so having thousands of seedlings clustered around the parent’s skirts where they will never thrive, lifting and nurturing seems a good option.
The coum flowers are less obviously shuttlecocked than their autumnal cousins, C. hederifolium, which are equally prolific and fecund. At least with the hederifolium, I no longer bother to hand pollinate the flowers, since for the last 2 years, probably since our hay meadows have become more floriferous and supportive of native bumble bees, I’ve noticed that Bombus pascuorum workers are regular, systematic visitors to the Cyclamen flowers in August to October.
Also known as sowbreads, (Pain de Porceau, Suabrot, Pain de Porcini) there are records of Cyclamen in the UK from the time of Gerard’s herbal (1597), and these common names indicate that the tubers are apparently relished by pigs, which would hunt them out from wooded environments.
Pig’s digestive systems are obviously well adapted to process them, since the raw tubers are toxic to people, causing violent diarrhoea, and potentially being fatal, thanks to their triterpene saponins. As little as 8 grams apparently being a lethal dose. Centuries ago Pliny the elder described how tuber extracts could be used to poison arrow tips, and fishermen in Sicily even used small doses in water to temporarily stun fish and make them easier to catch. Strangely however in some cultures in the Middle East, inquisitive folk evidently not deterred by such risks or stories discovered that roasting the tubers destroyed these toxins, and the tubers could then be enjoyed as a delicacy. Some even make a tea from the delicate petals. Click here for more interesting background on the genus by Dennis Carey and Tony Avent..
In mid December we headed to the National Botanic Garden of Wales (NBGW) for a pre Christmas Food Fair, and also to inspect their Ty Unnos (one night house) project.
This was an attempt to remind visitors of a custom peculiar to Wales originally developed by squatters, particularly in the poor and remote areas of rural Wales, that if you could construct a basic house on common land with walls, roof, a window, door and hearth and get smoke emerging from a hearth within a day then you were able to claim the land for yourself as freehold. In addition some versions of the Ty Unnos legends claim that the house builder was then able to hurl an axe from the newly built property and lay claim to the land lying within the circumference of where the axe landed. Click here for more on Ty Unnos, though little of certainty relating to this practice seems easily accesible on line.
As soon as we visited the site build, hidden behind woods close to the NBGW entrance, it was clear that this was going to be very different to some of the original Ty Unnos constructs which were probably simple affairs with turf walls and simple thatched roof. Much prepared timber, piles of Li – ion powered hand tools, and floodlighting were in evidence along with a well organised crew of volunteers doing the construction and assembly.
Leaving the site a couple of hours later, steady progress on the build had been made… and I popped in later still in the afternoon for some progress photos, when I had a fascinating chat with a fellow observer who filled me in on much distant local history including the Rebecca riots of the 1840’s when rural poverty and starvation, brought to a head by a series of disastrous weather years, left a lasting impact on the area.This is too big a topic for me to attempt a quick precis of, but click here for a very intelligent and thoughtful review, by Rhian E Jones, (author of Petticoat Heroes – Gender, Culture and Popular Protest in the Rebecca Riots) of the background, events and historical context of “Rebecca” in South West Wales and beyond.
Rhian explores some of the many questions she felt were left unanswered in her mind.
“Why had these men donned women’s clothing to protest? Why, when they had opposed workhouses, churches, bailiffs and landowners, were their subsequent memorialists only interested in tollgates? How did ‘respectable’ middle-class farmers end up fighting alongside proto-proletarian labourers from local coalmines and ironworks?”
Well worth reading.
Back to the NBGW on the last day of the year, to see how the building ended up. The builders had left, evidence of a central fire pit remained, though no smoky timber traces. And outside a sea of mud…
More evidence of the challenging weather for the last 6 months really, and in the garden few visitors, just moody light and dodged showers …And as if to reinforce the Christmas CD we’d listened to just before leaving, storm Dylan powered in and turned my new umbrella inside out bending rays as I stood against the light in the teeth of a gust, as showers from the pool’s lip flew and the silvered Dragon’s tail of the broad walk rill snaked deserted to the gate and distant rising hill.
Happy 2018, and thanks for reading.
Addendum ...With New Year’s Eve activities trundling on whilst I tried to get this post finished before 12 pm, I couldn’t include the following circular synchronicity snippet. After the enjoyed Dylan Thomas poetry, (for anyone interested, click here for the CD we bought), I’d googled to see what original signed poetry by the great man was available.
Top of the list, in terms of price (!) was a first edition, first impression, presentation copy of Thomas’s first book, simply titled 18 poems. To quote from the sale details…
18 poems was Thomas’s first book, published in an edition of only 500 copies shortly after his 20th birthday, with 250 sets of sheets bound and sold a year after the first issue. This is one of the second issue copies with the Parton Press advertisement tipped-in between the half-title and title. Both issues are rare today, particularly so in the dust jacket and with presentation inscription inscribed by the poet on the front free end paper,
The inscription reads:
“To Nora from Dylan, March 1938” .
And just who was “Nora”?
To quote again from the seller’s interesting notes…
The recipient was Nora Summers (1892-1948), an artist and the lover of Yvonne Macnamara, Thomas’s mother-in-law. Nora had studied at the Bristol School of Art and then the Slade in London, and married fellow artist Gerald Summers in 1912. In 1914 she became close to the family of painter Augustus John, and through him Yvonne and the Macnamara children, with whom she and Gerald lived communally for a few years. Yvonne and Nora’s relationship was intense, and Caitlin ( Yvonne’s daughter, and subsequently Dylan’s wife) later remembered Nora as “the father figure of our girlhood and an evil one”, but the two fiery women did see eye-to-eye about art, with Caitlin acting as a model for Nora’s burgeoning photographic hobby. Nora also enjoyed entertaining the young artistic friends of the Macnamaras, including Dylan Thomas, and she took a number of now-iconic photographs of the poet, including the image of Thomas smoking, and the photograph of the poet and his wife at Brown’s Hotel in 1938.
So why the synchronicity? Fiona and I had called in at a local craft fair just before Christmas and found 3 lovely small bud vases which I thought would be brilliant for holding and photographing individual snowdrops. So for Christmas this year, our table had been graced with 4 flowers from our favourite snowdrop, which had been “open” this year from the middle of November. Except outside, the flowers rarely open wide in the cold and damp. Brought into the warmth of the house, the flowers soon opened fully, and from just these 4 flowers, the honeyed scent then released was wonderful.
And what is this snowdrop called? Well, Mrs.(i.e Yvonne) Macnamara. Since it was she who was the original source of this fantastic snowdrop.
Oh, and if you wanted to own this rare book of poetry, with a tenuous link to the world of snowdrops, how much would it set you back? Click here for some photos of what you’d be getting – though not interestingly a list of what poems are included!!. And check your bank balance, since the asking price is £8,750!!!