Heat is good for snowballs

There are a few, perhaps, who would agree with Oscar Wilde that the Alps are objects in the worst possible taste

There are a few, perhaps, who would agree with Oscar Wilde that the Alps are objects in the worst possible taste. But more would incline to the sentiments of the anonymous poet who said:

He who hath seen the eternal snows,

Noonday white and evening rose,

Though he descend down to the plain,

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Never is the same again.

The height to which one would have to ascend to encounter these eternal snows varies with the latitude. In the case of Mt Erebus in Antarctica, for example, one does not have to ascend at all: the permanent snow-line is at the surface.

In Switzerland the permanent snow-line lies somewhere around 6,000 or 7,000 feet above sea level, while in the case of Mt Kilimanjaro, almost on the Equator, the zone of permanent snow is some 15,000 ft above the surface.

This variation of susceptibility to snow with height is mirrored in our own country in the sense that, when snow is on the cards, it is much more likely to fall on high ground than near sea level.

The average rate of decrease in temperature with height in the atmosphere is about 20C per 1,000 ft, and may be considerably more. So it is often cold enough for snow on hills and mountains even when the temperature nearer sea level is 6C or 7C.

But wherever snow falls in Ireland the temperature is never far from zero, and this has interesting consequences. Close to the melting point, the tiny hexagonal ice-crystals of which snow is formed retain a thin film of liquid water, and therefore adhere together easily.

This facilitates the formation of our large Irish snowflakes; at very low temperatures there is less aggregation, and so foreign, continental flakes are usually smaller.

For this same reason - because its temperature is rarely far from zero - Irish snow is good for snowballs. In the process of making a snowball, compression of the snow by the hands causes dramatic increases in pressure near the pointed ends of the individual ice crystals and this in turn - unless the temperature of the snow itself is very low indeed - causes localised melting to take place.

Then, when the pressure is removed, the water produced by the melting freezes again, and joins neighbouring crystals firmly together to produce a nice firm snowball.

In very cold snow, as often found in Scandinavia and on the Continent, this useful temporary melting, and therefore the subsequent re-freezing which cements the ball, cannot take place quite so readily - so it is harder to make snowballs.