Glacières; or, Freezing Caverns

by Edwin Swift Balch

“This being the case, if the water contained in the pebbly mass had a temperature above the freezing point, the heat would be but imperfectly transmitted to the frost, through the clay, provided there was no other way for its escape. But we have seen that the stratum of clay that overlays the bed of pebbles in the side of the gravel pit was not horizontal, but inclined towards the well at an angle of 25°. Now if this drip was continued to the well, and existed there (which is highly probable), it will be seen that the ascending current of heated air, in the pebbly bed, would be checked upon meeting the overlying barrier of clay and be deflected out of its upward course. The tendency of heated air is to rise, hence it would continue its course along the under side of the clay, through the interstices in the bed of pebbles, till it found a place of escape at the surface, which in this case may have been at the gravel pit before named.”

Professor Edward Hitchcock wrote in 1861: "The presence of a mass of frozen gravel deep beneath the surface in Brandon, was first made known by digging a well in it in the autumn of 1858. * * * The gravel, also, rises into occasional knolls and ridges. In short, it is just such a region of sand and gravel as may be seen in many places along the western side of the Green Mountains; and indeed, all over New England. It is what we call modified drift, and lies above genuine drift, having been the result of aqueous agency subsequent to the drift period. * * * The well was stoned up late in the autumn of 1858, and during the winter, ice formed upon the water in one night, two inches thick. It continued to freeze till April; after which no ice was formed on the surface, but we can testify that as late as June 25th, the stones of the well for four or five feet above the surface of the water were mostly coated with ice; nay, it had not wholly disappeared July 14th. The temperature of the water was only one degree of Fahrenheit above freezing point. The ice did however disappear in the autumn but was formed again (how early we did not learn) in the winter, and so thick too that it was necessary to send some one into the well to break it. We visited the well August 18th, 1860, and found the temperature 42°. Yet only the week previous ice was seen upon the stones, and we were even told by one of the family, that a piece of ice had been drawn up the day before in the bucket. * * * These frozen deposits may have been produced during the glacial period that accompanied the formation of drift, and continued far down into the subsequent epochs of modified drift. * * * But in all the excavations both gravel and clay occur: and how almost impervious to heat must such a coating 20 feet thick, be! It would not, however, completely protect the subjacent mass from solar heat. But there is another agency still more powerful for this end, namely, evaporation, which we think has operated here, as we shall more fully describe further on; and we think that these two agencies, namely, non-conduction and evaporation, may have preserved this frozen deposit for a very long period, from exterior influences."

Professor Thury in 1861 says about Saint-Georges: "Such is the résumé, concise but exact, of the results of our winter excursion. They furnish proof to the fact generally borne witness to by the mountaineers, that ice does not form in winter in the interior of caverns. But if this is so, it is for a very simple reason: two things are necessary for the formation of ice: cold and water. In winter, the cold is not wanting: but if there is no spring opening in the cave, the water is absent, and then no ice forms.

“It is in the spring, at the time of the first melting of the snows, that the ice must form. Then water at 0° pours over the surface, and penetrates by the fissures of the rock and by the large openings into the chilled cavern, which is also receiving the freezing air of the nights. The grotto then makes its annual provision of ice, which after this could only diminish little by little during the whole duration of the warm season.”

Professor Thury writes about the Grand Cave de Montarquis: “Here it must be when water and cold meet, that is autumn and especially spring, the time of the first melting of the snows.”

“During the winter * * * the colder, heavier air comes to freeze the water of the grotto, and chill the ice and the wall of rock.”

“During the summer, the radiation of the vaults and the proper heat of the ground only melt a small quantity of ice because this absorbs much heat to pass into a liquid state.”

“The heat of the air is entirely used to melt the ice; it does not therefore manifest itself as sensible heat.”

“The contact of the ice ready to melt, plays in a certain way, towards the air a little warmer than itself, the rôle of an extremely absorbing body, or one which has an excessive caloric conductibility.”