Glacières; or, Freezing Caverns

by Edwin Swift Balch

“Here the formation of the ice could not possibly be attributed to the cold caused by evaporation. The psychrometer indicated ninety-two per cent, of relative humidity: the atmosphere of the grotto was therefore almost saturated with evaporation of water, and the maximum of cold caused by evaporation was not over half a degree centigrade.”

About prismatic ice and a hollow pyramid, he says: “The prismatic (aréolaire) structure is produced later on in the ice, by a new and particular arrangement of the molecules of the already solidified water. Therefore the recent stalactites are never crystallized.”

“In the beginning of the hot season, the atmospheric temperature of the grotto rises slowly. Inferior to zero by some tenths of a degree, it produces first on the surface, in the stalactites, the prismatic structure. The temperature continues to rise, the central portions of the stalactites, still composed of ordinary ice, liquefy, and if the melting water finds some issue, either by accidental openings left between some prisms, or by the extremity of the stalactite or by some point of its surface which had escaped the action of the regular crystallization; by this opening the water escapes, and the tubular stalactite has been formed.”

“The column was composed of a very special ice, perfectly dry, perfectly homogeneous, translucid and whose appearance could only be compared to that of the most beautiful porcelain. I am inclined to believe that we had under our eyes a special molecular state of congealed water. This state would be produced under the influence of a constant temperature of a certain degree (Note—perhaps not far from 4°—the actual temperature of the grotto) long prolonged. These causes can be realized more completely in glacières than anywheres else.”

The Reverend George Forrest Browne, published in 1865, Ice Caves in France and Switzerland, one of the most delightful books of travel ever written, on account of the scientific accuracy and the humor of the author. He visited La Genollière, Saint-Georges, Saint-Livres, Chaux-les-Passavant, Monthézy, Arc-sous-Çicon, the Schafloch, Haut-d’Aviernoz, which he calls Grand Anu, Chapuis, and Font-d’Urle. He says: "The view which Deluc adopted was one which I have myself independently formed. * * * The heavy cold air of winter sinks down into the glacières, and the lighter warm air of summer cannot on ordinary principles of gravitation dislodge it, so that heat is very slowly spread in the caves; and even when some amount of heat does reach the ice, the latter melts but slowly, for ice absorbs 60° C. of heat in melting; and thus, when ice is once formed, it becomes a material guarantee for the permanence of cold in the cave. For this explanation to hold good it is necessary that the level at which the ice is formed should be below the level of the entrance to the cave; otherwise the mere weight of the cold air would cause it to leave its prison as soon as the spring warmth arrived. In every single case that has come under my observation, this condition has been emphatically fulfilled. It is necessary, also, that the cave should be protected from direct radiation, as the gravitation of cold air has nothing to do with resistance to that powerful means of introducing heat. This condition, also, is fulfilled by nature in all the glacières I have visited, excepting that of S. Georges; and there art has replaced the protection formerly afforded by the thick trees which grew over the hole of entrance. The effect of the second hole in the roof of this glacière is to destroy all the ice which is within range of the sun. A third and very necessary condition is, that the wind should not be allowed access to the cave; for if it were, it would infallibly bring in heated air, in spite of the specific weight of the cold air stored within. It will be understood from my description of such glacières as that of the Grand Anu, of Monthézy, and the lower glacière of the Pré de S. Livres, how completely sheltered from all winds the entrances to those caves are. There can be no doubt, too, that the large surfaces which are available for evaporation have much to do with maintaining a somewhat lower temperature than the mean temperature of the place where the cave occurs."

Browne noticed prismatic ice several times. He says of it: "M. Thury suggests also, as a possibility, what I have found to be the case by frequent observations, that the prismatic ice has greater power of resisting heat than ordinary ice. * * * A Frenchman who was present in the room in which the Chemical Section of the British Association met at Bath, and heard a paper which I read there on this prismatic structure, suggested that it was probably something akin to the rhomboidal form assumed by dried mud; and I have since been struck by the great resemblance to it, as far as the surface goes, which the pits of mud left by the coprolite workers near Cambridge offer, of course on a very large scale. This led me to suppose that the intense dryness which would naturally be the result of the action of some weeks or months of great cold upon subterranean ice might be one of the causes of its assuming this form, and the observations at Jena would rather confirm than contradict this view: competent authorities, however, seem inclined to believe that warmth, and not cold, is the producing cause."

Mr. Browne found a hollow cone at La Genollière, for which he accounted as follows: "In the loftier part of the cave * * * ninety six drops of water in a minute splashed on to a small stone immediately under the main fissure. This stone was in the centre of a considerable area of the floor which was clear of ice. * * * I found that the edge of the ice round this clear area was much thicker than the rest of the ice on the floor, and was evidently the remains of the swelling pedestal of the column. * * * When the melted snows of spring send down to the cave, through the fissures of the rock, an abundance of water at a very low temperature and the cave itself is stored with the winter’s cold, these thicker rings of ice catch first the descending water, and so a circular wall, naturally conical, is formed around the area of stones; the remaining water either running off through the interstices, or forming a floor of ice of less thickness, which yields to the next summer’s drops. In the course of time, this conical wall rises, narrowing always, till a dome-like roof is at length formed and thenceforth the column is solid." From what I have observed myself, this explanation seems to fairly meet the facts.

Professor T. G. Bonney, in 1868, was inclined to believe that there was some connection between glacières and a glacial period.

Mr. W. R. Raymond, in 1869, concluded from his own observations about the lava cave in Washington: that the cold air of winter freezes up the percolating waters from the surface, layer upon layer, solid from the bottom, and the accumulated ice thaws slowly in summer, being retarded by the covering which keeps out the direct rays of the sun, and by the fact that the melting ice at one end of the cave, through which the summer draught enters, itself refrigerates the air and maintains a freezing temperature at the other end.

Dr. C. A. White, in 1870, says of the cavern at Decorah: “The formation of the ice is probably due to the rapid evaporation of the moisture of the earth and rocks, caused by the heat of the summer sun upon the outer wall of the fissure and valley side. This outer wall is from ten to twenty feet in thickness where the ice was seen to be most abundant. The water for its production seems to be supplied by slow exudation from the inner wall of the cave.”