THE SONADON GLACIER.
To face p. 266.
Our knowledge of the glacier world in its formative processes is as yet extremely deficient. What proportion of the year’s snowfall—within the glacier region—is actually converted into ice? What proportion melts away on the surface and passes directly into water, to be carried away, carrying along with itself some of the ice? What proportion is, by sublimation and evaporation, returned to the atmosphere, to become again the toy of winds, in the shape of snow or rain-clouds, never feeding the glacier at all on which it first fell?
On the other hand, who can tell how much ice is formed on the glacier surface by the direct absorption of the air moisture collecting upon such a condensator? And would it be alien to our subject to ask what effect may have on the present glaciers the loss of pressure consequent upon the enormous reduction in bulk and height which they have undergone? Is the glacier ice formed under the present rate of pressure capable of offering anything like the same resistance to disintegration as its prehistoric congener? What are its powers of self-preservation under the vastly inferior pressure which it experiences in the very places in which ice was once packed to a height and in a bulk we should not like to express in figures, even if we possessed competent data?
The broad fact seems to be that as much snow as falls on the glaciers throughout the year is taken back into the atmosphere, and that the snow congealed and fixed in the upper basins is as nothing compared with the quantity of water that evaporates or runs away at the nether end of the mass every summer. What is the capacity of the ice-forming firn of the Aletsch basin compared to the extent of its melting surface? And how much snow does the firn receive every year from the atmosphere? And how much of that snow is incorporated?
There are now so many approaches to the glacier world of Switzerland that it should be easy to determine, at the outlet of a few typical glaciers, the amount of water thaw conveys to the valleys below. According to the season, it is quite easy to distinguish between rain-water, water from springs, and glacier water. Such observations would lead to results reciprocally verificatory.
My provisional conclusions are that:—
1. The snow falling on the Swiss glaciers is a mere fraction of the quantity wanted to assure their stability.
2. The average snowfall of any year returns to the atmosphere.
3. The source and means of congealation are not proportionate to the exigencies of ice-formation, even for the maintenance of the status quo.