Glacières; or, Freezing Caverns

by Edwin Swift Balch

The proofs, to my mind, of the truth of this view are: 1—Glacières are always found in parts of the world where, during part of the year at least, the temperatures of the surrounding country fall below freezing point. 2—All observations by reliable observers show that the temperatures of glacière caves vary, but in a much narrower thermometric scale, with those of the outside air: that the temperatures are lowest, and as a rule below freezing point, during the winter months; and that the temperatures are highest, and as a rule above freezing point, during the summer months. 3—Ice is never found far from the mouth of caves, but always near enough for the cold air to get in. 4—Evaporation, according to my observations, is, as in all other forms of ice in nature, connected mainly with the melting, not the freezing of the ice.

Geographical Distribution and Altitudes.—Glacière caves proper are found in various parts of Europe, Asia, and America, mostly in the smaller mountain ranges or in the outliers of the snowy mountain chains; generally in limestone and occasionally in basaltic formations. There are a good many in the Jura; a few in the Swiss and the Italian Alps; a number in the Eastern Alps of Tyrol and Carinthia. There are some in Hungary, several in Russia, one in Iceland, one on the Peak of Teneriffe, a number in Siberia, one in Kondooz in Central Asia, one in the Himálaya, one in Japan, and one in Korea. I have heard so far of over fifty glacières in North America, several of which are in Pennsylvania. From all over the world there are some three hundred places reported where subterranean ice is said to occur. This includes gorges, boulder heaps and freezing mines and wells, all of which exist in much the same localities as glacière caves.

All the glacières which I know of, are situated in a latitude or at an altitude where ice and snow forms for part of the year in the surrounding open country. None are reported from India or Africa, or in fact from any low-lying places in tropical latitudes. Most of them are found in middle latitudes, and only where during part of the year, at least, there is a cold season, that is, where for some time the thermometer stands below freezing point.

Glacières are, in general, at fairly high altitudes. The Schafloch is at 1780 meters; Skerisora in Transylvania at 1127 meters; Dóbsina at 1100 meters; the Glacière de Saint-Georges at 1208 meters. It is true that there is one freezing cavern in the sub-tropical latitude of Teneriffe, La Cueva de la Nieve; but it is at an altitude of 3300 meters, and where snow falls every year in the open on the Peak. Unless some freezing cave is hereafter discovered in a region where there is no ice in the open in winter, I do not see how the imperative necessity of the cold air of winter for forming the supply of ice can be controverted.

Thermometric Observations.—That the cold air of winter is the important factor in the production of cold is proved, also, by the thermometric observations recorded in various caves by different observers. They all tell the same tale: that the temperatures vary with those of the outside air, that they are lowest in winter and highest in summer. I quote in the “List of Glacières”[57] a few of those published; but there are many more, and they all show the same general characteristics.

[57] See Part III.: Decorah, [page 178]; Chaux-les-Passavant, [pages 203-5]; La Poujade, [page 208]; Montarquis, [page 218]; Saint-Georges, [page 219]; Schafloch, [page 223]; Kolowratshöhle, [page 227]; Schellenberger Eisgrotte, [page 228]; Frain, [page 252]; Dóbsina, [page 253]; etc.

A comparison of all the figures recorded proves that, as a rule—inside of glacière caves—from about the first of November to the first of July, there are winter temperatures, that is temperatures below freezing point; and from about the first of July to the first of November, there are summer temperatures, that is temperatures above freezing point.

The observations prove also that the inner temperatures vary less than the outer, that is that they range within narrower limits. They also show that the inner air is but slowly affected by the outer air when the latter is above freezing point, the inner temperature rising then only gradually. Per contra, when the outside temperature drops quickly much below freezing point, the inside temperature generally drops correspondingly at once, proving that the cold air has sunk by its weight into the cave. The observations also prove that the old idea that the temperature of caves is the same throughout, can no longer be considered correct. The observations also appear to show, that the temperature of a cave does not necessarily represent the mean annual temperature of a surrounding district. Observation is still entirely lacking on the mean annual temperature of glacières, so that one cannot speak definitely about the matter; but it seems likely that the mean annual temperature of a glacière cave is lower than the isotherm of its locality; and it seems more than probable that on the same isotherm different glacière caves may have different mean annual temperatures, varying with the elements of size, quantity of ice, position of body of cave and of entrance, water supply and other factors.

Ice near the Entrance of Caves and the Surface of the Soil.—An important proof that it is the cold air of winter which forms the ice is the fact that the latter is always found near the entrance of caves or near the surface of the soil. It never extends far within. To the best of my knowledge, ice has never been found two hundred meters from the entrance nor at any depth beyond one hundred and fifty meters. In all caves of great extent, the temperature far in is about the same as that of the surrounding rock, and in all deep borings the temperature increases with the depth and at great depths the temperature becomes high. This nearness of subterranean ice to the outside air is one of the best proofs, that, paradoxical as the whole phenomenon appears at first, yet in reality it is an extremely simple matter.

The position of the entrance of a cave in relation to the body of the cave is an important factor in permitting the cold air to permeate and remain in the cave. In all the caves or gullies I have examined myself, the main mass of ice is well below the level of the entrance, and even if the latter is sheltered against the wind, it is not sheltered against the cold air of winter. This is heavy, and by its own weight sinks well down to the bottom, freezing up in course of time all the moisture that may drip from the roof, or that may come into the cave in the shape of melted snow or cold winter rain. The summer air, which is warm and, therefore, light, can only enter the cave with great difficulty; and, as a rule, before it dislodges the winter air and destroys the ice, another winter’s freeze reverses once more the conditions. These principles seem to hold of every known glacière. It is true, that at the Frauenmauer, the floor of the cavern rises somewhat from the entrance; but the highest point of the floor is still below the level of the top of the entrance, so that the cold air can flow over the highest point without difficulty. The same appears to be the case at the Posselthöhle; while at Amarnath in Kashmere, where the floor is said to rise to the back wall, the entrance is about as large as the area of the floor, so that the ice must also be below the level of the top of the entrance.