Sir,

The comments by Professor Cross on Dr. R. Streiff-Becker’s conclusions in “Glacier advances apparent and real” are in general quite valid and pertinent. The growth of the Nisqually and other glaciers in the Cascade Range is unquestionably genuine. Similar growth has also been reported from regions outside the United States. There is ample evidence to refute the belief that glaciers are shrinking everywhere. The tendency to seek other explanations for glacial advances and the reluctance to accept the possibility of climatic change, even for short intervals, are hardly justified.

Figures 2 and 3 in the original article were intended to show the nature of the changes in the active front in uniform intervals of two years. No discussion of the complex behavior at higher altitudes was included. However, the omission of complete dates for these photographs was an oversight. Figures 2 and 3c were taken 17 August 1955. Figures 3a and 3b were photographed 3 August 1951 and 12 August 1953. While an interval of two weeks can produce striking changes in the exposure of rocks above a snowfield, there are other more important factors which complicate the problem. Similar pictures taken at approximately two-week intervals throughout several seasons indicate that the altitude of maximum snowfall varies widely in different years. Accurate conclusions should not be attempted from the meagre data in three photographs.

With respect to Professor Cross’s criticism of the estimated lag of 50 years in the germination of coniferous trees, used in dating the time of previous advance, I would like to point out that the 1855 date is generally in agreement with historical glacial advances elsewhere in the world. This lag is not inconsistent with the measured lags of 35 and 50 years after the advances in 1883 and 1907. Agreement with other investigators in other regions would hardly be expected when a similar lag can be verified quickly by an inspection of the area vacated by the ice after 1907.

Soil conditions in the Kautz mudflow area and on Alaskan moraines are probably quite different from the conditions produced by the advance of a relatively clean glacier, followed by an abrupt retreat. The difference between germination lags below the Nisqually Glacier and in Alaska has been discussed with Dr. D. B. Lawrence and could be the result of a radical difference in available moisture. Chemical constituents of the rocks involved in a particular advance could also be a factor.

A. E. Harrison

Professor of Electrical Engineering

University of Washington Seattle 5, Washington 2 May 1958