Notes on Ground-Ice.

Oldham R. D., (1894), Notes on Ground Ice, Natural Science 4, 450-452

Every student of geological text-books and many observers of nature must be aware of the fact that ice sometimes forms on the bottom of running streams, instead of on the top, as invariably happens with standing water. Sixty years ago the knowledge of this fact seems to have been almost confined to the unlearned, and its reality was denied by the natural philosophers of the day; it has now become one of the elementary facts of physical and geological science alike, and is only doubted by some few, like Mr. Leslie in his charming Letters to Marco, who, though keen observers of nature, make no pretence to be regarded as scientific authorities.

The subject is referred to in every text-book of geology, principally from the point of view of the action of this form of ice in modifying the shape of the earth's surface, and tbe question of its mode of origin is treated in a more or less imperfect, where not inaccurate manner. The standard account, to which reference is often made, was published in 1833 by Arago,[1] whose paper is principally devoted to a proof of the reality of the phenomenon, which appears at that time to have been generally regarded as incompatible with tbe fundamental laws of nature. The theory advanced by him was that, owing to the swirls and eddies of the current, the whole body of the stream is reduced to freezing point [2], and that in this water the stones and weeds on the bottom serve as so many nuclei for the ice crystals to form upon.  Within two years of the publication of this theory a totally different one was broached [3], and supported by some careful and instructive observations. According to this the formation of ground­ ice is due to loss of heat by radiation from the stones on the bottom, which are thus cooled below freezing point, and so give rise to the growth of ice crystals in a manner analogous to the formation of hoar frost.

These two are the theories found, in one form or another, in nearly every text-book, and of them the latter appears to enjoy the greater popularity, a result probably of its greater ease of comprehension, as much as of the observations to whIch it was conjoined. There are, indeed, certain facts which seem to support this theory, such ds the general consensus of observers that ground-ice is only produced in clear water, and on cloudless nights, when radiation is most active; and Mr. Farquharson in his paper lays stress on the fact that it was not found near the piers of a bridge, close to an embanking wall, or under a grass-clad bank. This is, however, explicable in other ways than by radiation having been checked by these objects, and as regards the first part of the argument the coincidence may well be due to the fact that sharp frosts seldom occur in temperate latitudes except in cloudless weather, while the clearness of the water is as much a necessity of the first-named theory as a support of the second. Moreover, if there were any truth in the assumption, that the clear water of a stream flowing over a stony bottom is cooled to any important extent by radiation from the stony bottom over which it flows, this would be equally true in the case of standing water. But such we know is not the case, and it is the fact that the loss of heat takes place principally from the surface of the water, combined with its expansion and consequent decrease of density as the freezing point is approached, that makes our ponds freeze first on their upper surfaces.

Against the other theory, that the pebbles on the bottom merely act as nuclei on which the ice crystallises out from water cooled down below freezing point, it might be urged that this cannot occur with water such as is met with in nature, but only after it has been distilled or otherwise cleared of all dissolved air and solid particles. Tbis, however, is not altogether the case. I have myself observed the cooling of water below freezing point when no special precautions had been taken. While camping in the desert of Western Rajputana it was a common experience to find, after a clear and cloudless night in January and February, that the water in my wash hand basin was frozen over, and frequently frozen solid. On one occasion, after a cold night, I was surprised to find that the water was unfrozen, and, thinking that perhaps the night had not been so cold as I imagined  (I had not then examined my thermometer) I plunged my hands into the water, which immediately became converted into a pasty mass of ice crystals and water. Here ordinary well water, in a basin which was only clean in the common sense of the word, had cooled below freezing point wIthout soldifying; but the occurrence was an exceptional one, and it may well be doubted if it could take place as an ordinary event in the waters of a stream.
There is yet a third theory, originally published in 1816 [4] which appears to have been almost completely lost sight of since, that ground ice is due to the presence of numerous minute crystals of ice in the ice-cold water; these are carried to the bottom of the stream by the eddies and there, coming into contact with stones and weeds, are collected and frozen together into a tangled mass of spongy ice.  It is probsable that ice cystals are always present when ground ice is being formed, they are specifically mentioned by Knight [5], by Eisdale [6], who thought they originated in the air and then fell into the water, and by Rae [7], while the only observations which my limited opportunities have enabled me to make , tends to show that the accumulation of small ice crystals independently formed in water of the stream is a most important factor in the production of ground-ice.

In May, 1888, I was encamped at Karzok, on the shores of the Tso Moriri, at an elevation of close on 15,000 ft. above the sea. The camp was pitched on the edge of a small oasis of cultivation, and the irrigation channel, which supplied the fields, flowed not far from the door of my tent. The night had been a cold one, and in the morning, while the ground was still hard with frost, I noticed that the water in the irrigation channel had risen and overflowed its banks; as this water was derived from the melting of snow on the hills, it should have been at its lowest in the early morning, and the rise of the water duripg the night made me look for the cause of so unexpected an occurrence. I found tha! a sheet of semi-opaque, whitish ground-ice had formed on the bottom of the channel and so raised the level of the water, and that the ice was still growing. As the depth of the channel was under a foot, the process was an easy one to observe, and I was able to notice that the water was full of minute crystals of ice, which were swept along by the current, and, coming into contact with the surface of the ice on the bottom, became entangled in the irregularly disposed crystals of which it was composed and frozen into one solid mass with them. Owing to a diversion of the stream, consequent on its rise of level, I was also able to observe the gradual formation of a continuous sheet of ice. At first the ice crystals accumulated against stones and weeds in the bed, and principally on the up-stream side, as was observed by Knight in 1816; but as the numerous small local clusters of crystals grew in size they coalesced to form a continuous sheet with an irregularly upper surface.
From these observations it would seem that the earliest theory proposed comes so near the truth that the neglect it has met with is not justified. The crystallizing out of water reduced to or slightly below freezing point is doubtless a cause, and may in some case be the most important one in the formation of ground-ice; but the process is aided to a much larger extent than is generally recognized by the entanglement and accumulation of ice crystals formed and floating in the water.

R. D. Oldham

1 Arago, Januaries du bureau des Longitudes, 1833. pp. 244-268,
2 See Desire Leclerq, Mem. Cour. Acad. Roy. Bruxelles, 18. (1845) for observations confirmatory of this.
3. Farquhausen, J., (1835). Phil Trans, 125, 329-343, 1835
4. Knight, T.A. (1816). Phil. Trans., pp. 286-293
5  Knight, T.A. (1816). Phil. Trans.,  286
6  Eisdale, (1834) Edin. New Phil. Journ. 22, 167-171,
7  Rae, (1899) Nature, 21,538