The Editor,

The Journal of Glaciology

Sir,

The discussion on crevasse depths in the Journal of Glaciology, Vol. 2, No. 15, 1954, p. 339, leaves me in some doubt whether crevasses in temperate glaciers cannot exceed 30 m. in depth. On the Ebnefluhfirn in the Bernese Alps, at a height of about 3700 m., I once pulled a man from a snow bridge in a crevasse at a depth of 28 m. below the surface level. He had crashed through two higher snow bridges to land on one which spanned the crevasse where it was still wide open. Miraculously he was not injured. As he was in the crevasse for over two hours his eyes must have become well adapted. He stated that the open crevasse continued to a considerable depth below the snow bridge, and this was confirmed by the time taken by snowballs to fall to the bottom. This crevasse must have reached at least the maximum depth of 120 ft. (36.5 m.) mentioned by Mr. Miller.

The pronounced bulging claimed by Dr. Nye for walls exceeding 34 m. would apply not only to crevasses but to all ice walls. Glacier fronts in Greenland have often been found to reach twice, and occasionally three times, that height above the fjord level, but no marked bulging near the water level has been observed (see, for instance, E. Sorge, Umiamako- und Rinkgletscher, Universal- Grönland-Expedition 1932). It may be objected that, due to calving, the ice walls near the front of the glacier are changing too rapidly to allow marked bulging. But there are in the Arctic, as in the Antarctic, great numbers of stranded icebergs with walls considerably higher than 30 m. above the water, for instance on Jakobshavn Iceberg Bank. They often remain in the same position for many months, and occasionally for more than a year. I do not know of any observations which show that they bulge markedly under their own weight. These icebergs generally derive, at least in the Arctic, from low-lying glacier tongues whose surfaces melt to a depth of several metres every year. As much of this melt water infiltrates, and a considerable fraction of it transfers its heat of fusion to the ice by freezing, the temperature of most of these icebergs cannot be considerably, if at all, below freezing point (Expéditions Polaires Françaises, Serie Scientifique, No. 10, 1949 [1950], p. 30). The absence of yielding, therefore, cannot be attributed to a low temperature.

But it should be noted that according to Dr. E. Orowan (Journal of Glaciology, Vol. 1, No. 5, 1949, p. 235) the critical height of 10 to 30 m. applies only to ice columns with a height greater than their width, and not to ice slabs with horizontal dimensions comparable with their height. Therefore only the height of seracs or the depth of crevasses in a heavily dissected area would be limited in this way; more widely spaced crevasses, such as are generally found in the névé area or the walls of compact icebergs or stagnant glaciers, could exceed 30 m. in height even if their temperature were at freezing point.