Glacières; or, Freezing Caverns

by Edwin Swift Balch

[I.]

Terminology.—Ice enduring the entire year is found, in temperate latitudes, in a variety of forms and in several different kinds of places. In some cases it is entirely above the surface of the earth; in others it is entirely beneath the surface of the earth. These are the extremes, and between them there are certain intermediate forms. The perennial ice above ground of temperate regions has gradually become known in English by the French word glacier, but strange to say, there is no term in use in English which accurately describes the perennial ice formations which are partially or completely underground. Thus the term “ice cave” is applied to a rock cavern containing ice, and the term “ice gorge” to a rock gorge containing ice. Both terms are misleading, because the character of the contents is mentioned before the nature of the geological formation. We say correctly enough “limestone cave” or “lava cave” and, in my opinion, we should apply the term “ice cave” in a similar manner to the hollows in the ice at the lower end of glaciers, whence the glacier waters make their exit. These are really “ice caves,” that is caves with sides and roof made of ice. Another trouble of the term “ice cave,” as applied to rock formations containing ice, is that it is not generic: not only is it incorrect, but also it is not comprehensive. It does not apply to mines, tunnels, wells, gullies, boulder taluses, or underground ice sheets. If “ice cave” is used, except in its true sense of glacier ice cave, it seems at least as though it should be so only for real caves which retain ice, as opposed to taluses and wells. Curiously enough, the Germans are just as inaccurate as ourselves, for their terms eishöhle and eisloch are absolute translations of our “ice cave” and “ice hole.” Indeed, there is no doubt that some of the incorrect notions about subterranean ice formations, are due to the inaccuracy of the terminology.

The only language, so far as I know, which has a correct and really generic term for subterranean ice formations, is the French in its word glacière. The French and Swiss say glacières naturelles of ice deposits formed naturally underground; and glacières artificielles of ice houses. Glacière naturelle is comprehensive and accurate. It covers all the rock formations and suggests also the mode of formation of the ice. It likewise implies the strong resemblance between natural ice deposits and artificial ice houses. It might be well, therefore, if the French term glacière were adopted as a generic term for all underground ice formations. As, however, there is little likelihood of this happening, the question arises as to the best English equivalent or equivalents. These seem to be “freezing cavern, freezing talus,” etc., “natural refrigerator” or “subterranean ice formation.” “Natural refrigerator” and “subterranean ice formation” are more generic than “freezing cavern, freezing well,” etc.; but the latter have the advantage of suggesting immediately that reference is made to the hollows of the earth which at times contain ice; and, therefore, they are the best terms, perhaps, which can be chosen in English.

Another point in the terminology of this subject has reference to subterranean hollows where draughts issue or enter. Such hollows are found in all parts of the world and are known usually in English as “blowing caves” or “cold current caves.” The Germans speak of them as windröhren or windlöcher. In my first paper about caves,[12] I used the word “windhole” which I translated from the German. The term “windhole” seems to me preferable to “blowing cave” or “cold current cave” in that it is more generic. It applies to taluses or boulder heaps, or in fact, to any hollows where draughts issue or enter, whether these hollows are genuine caverns or not.

[12] Ice Caves and the Causes of Subterranean Ice, November 1896, and March 1897.

It is necessary also to explain here that “glacière” and “windhole” are not synonymous terms. It must be understood that a glacière or natural refrigerator is a place where ice forms and endures in a subterranean or semi-subterranean situation; and that the presence of ice is the criterion of whether a place is or is not a glacière. Likewise it must be understood that a windhole or blowing cave is an underground hollow with at least two openings, and in which distinct draughts occur; and that the presence of draughts is necessary to constitute a place a windhole or blowing cave. A freezing cavern may or may not be a windhole, and a windhole may or may not be a freezing cavern.

Temperatures.—The phenomena of glacières are so closely connected with temperatures that it seems necessary at this point to mention some general facts in connection with subterranean temperatures, even if these still form a subject of some uncertainty, and one about which further observation is desirable. Subterranean temperatures may be grouped under three heads: 1, Ordinary or normal temperatures; 2, Temperatures above the normal or super-normal temperatures; 3, Temperatures below the normal or sub-normal temperatures.

1. In the great majority of caves, cellars and subterranean places of all descriptions, the temperature of the air is about the same, all the year round, as that of the ground. The frost of winter and the heat of summer penetrate the earth for some trivial distance, a few meters perhaps, and lower or raise the temperature of the ground temporarily. Below this there is a stratum where the temperature is found to vary but little the entire year and which, in a majority of cases, approximates the mean annual temperature of the district. Below this invariable stratum, the temperature generally rises slowly, not at exactly the same rate everywhere, but in a regular increase. This increase of temperature averages 1° C. for every 32 meters. As most caves and cellars are of small depth and as they take their temperatures from that of the ground, it follows that as a rule their temperatures are moderate and pleasant. And as the air of the majority of caves and subterranean hollows is about the same as the temperature of the surrounding rock, it is correct to call subterranean air temperatures closely approximating the ordinary temperature of the ground, ordinary or normal temperatures.

As already stated, with an increase of depth, there is, in almost all cases, a regular increase of temperature. For this reason, mines, which are much the deepest hollows reached by man in the surface of the earth, are, as a rule, warmer in the lower levels: if deep, they are also hot. And this is so generally the case that warmer temperatures at the bottom of mines may be considered as normal.