Glacières; or, Freezing Caverns

by Edwin Swift Balch

[62] Among those who have written that evaporation is a factor in the formation of subterranean ice, may be mentioned: Pictet, 1822; Scrope, 1827; Reich, 1834; Pleischl, 1841; Murchison, 1845; Olmstead, 1856; Hitchcock, 1861; White, 1870; Kirchhoff, 1876; Krauss, 1895.

I have already said that I believe it is the movements of the air which cause a cave to be a glacière cave or a normal cave. When they act in such a way as to permit the cold air of winter to permeate a cave, we find low temperatures and ice; when they do not, we find the temperature about the same as that of the ground and no ice.

That the ice is not formed in apparently static caves, by movements of air producing evaporation, seems to me proved by what I have noticed in regard to the atmosphere. The dryness or moistness of the air within a glacière cave is coincident with the state of freezing or thawing of the cave. When I have visited a large cave in June, everything was frozen tight, there were no drips nor mushy ice, the air was relatively dry and the sensation of cold not unpleasant. When I have visited a cave in August, the ice was soft and mushy, water was dripping from the roof, the atmosphere was moist, and the cold penetrating. It seems to me that the facts go to show that it is not evaporation which forms the ice, but the melting of the ice which fills the cave with moisture. If there are any draughts or movements of the atmosphere when above freezing point, then their tendency is to vaporize the ice.

The process of the formation of ice in relation to the atmosphere is as follows: the cold air permeates the cave and freezes up all the drip: the atmosphere becomes dry: gradually warmer air gets in and the ice begins to melt: then the atmosphere gets charged slowly with the vapor of the melting ice. This process is the exact opposite of the formation of ice by evaporation; it is the atmosphere which is made humid by the vaporizing of the ice, and by the drip. When the air is thoroughly saturated with the vapor, being scarcely renewed from outside and but a few degrees above freezing point, it undoubtedly retards evaporation, acts like a blanket and lessens the rate of melting of the ice.[63]

[63] See Part IV.: Thury, [page 285]; Fugger, [page 296]; Trouillet, [page 298].

Everything I have personally observed in freezing windholes shows that in them also the cold of winter and not evaporation is the cause of the ice. They answer to the same tests as other glacières, of geographical distribution and altitude, nearness of ice to the outside, thermometric observations, and dampness of the air when the ice melts. Equally with other glacières, the movements of air in windholes do not depend on the presence of ice, but the ice does depend on the movements of air and a water supply at the proper time. A proof that it is the cold of winter which makes the ice in windholes, is that the ice is always found at the lower extremity, for the reason that it is at that end that the cold air enters and to that end that the water gravitates. The reason that ice is more rarely found in windholes than in apparently static caves, is due to the movements of air. Unlike the caves where the heavy cold air preserves the ice by remaining pent up, as soon as the outside temperature rises the heavy cold air in windholes tumbles out at the lower opening and is replaced gradually by air at a higher temperature. This also flows out and when it is above freezing point, it naturally melts the ice and becomes humid: in fact, it vaporizes the ice as it passes, and dissipates the moisture into the outer air.

It is, however, certain, that in caves with a temperature some degrees above freezing point, when there is either running water or strong drips, evaporation may be, and sometimes undoubtedly is, a factor in lowering the temperature somewhat.[64] As in some windholes there is occasionally moisture on the rock surfaces where the air current passes, the evaporation from these surfaces doubtless lowers the temperature of the draughts, and it may be, also those of the rock surfaces, a little.

[64] See Part IV.: De Saussure, [page 274]. See also Les Abimes, 1894, page 564.

Further observations, however, will be necessary in regard to evaporation underground, as the data are still insufficient to make absolutely positive statements.[65] I fail to see any evidence to show that evaporation ever lowers the temperature of draughts underground below freezing point, only that it may help to lower them to something less than they would otherwise be. Taking all the facts which I have myself observed, and all I have read of in the reports of others, my own conclusion is that we have no proof that evaporation underground is ever strong enough to produce ice.

[65] Several observers consider evaporation as more or less of a factor in the production of cold underground. It is suggested also, that in certain cases, at high altitudes, evaporation tends to prevent the melting of the ice in windholes, but this is not proved, as yet. See Part IV.: De Saussure, [page 274]; Fugger, [page 296]; Trouillet, [page 298]; Martel, [page 300]; Lohmann, [page 302].