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Xerox University Microfilms 300 North Zeeb Road Ann Arbor, Michigan 48106 75-26,624 McSAVENEY, Maurice James, 1945- THE SHERMAN GLACIER ROCK AVALANCHE OF 1964: ITS EMPLACEMENT AND SUBSEQUENT EFFECTS ON THE GLACIER BENEATH IT. The Ohio State University, Ph.D., 1975 Geology X©rOX UniVOrSlty iviicrofilms , Ann Arbor, Michigan 48106 THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED. THE SHERMAN GLACIER ROCK AVALANCHE OF 1964: ITS EMPLACEMENT AND SUBSEQUENT EFFECTS ON THE GLACIER BENEATH IT DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Maurice James McSaveney, B.Sc.(Hons) The Ohio State University 1975 Reading Committee Approved by Dean Colin Bull Professor Richard P. Gc-ldthvi’ait Adviser Department of Geology Professor Tien H. Wu and Mineralogy THE SHERMAN GLACIER ROCK AVALANCHE OF 1964: ITS EMPLACEMENT AND SUBSEQUENT EFFECTS ON THE GLACIER BENEATH IT By Maurice James McSaveney, Ph.D. The Ohio State University, 1975 Dean Colin Bull, Adviser The Sherman Glacier rock avalanche in the Chugach Mountains of south-central Alaska fell during the great Alaska earthquake of 1964. The 10.1 X 10^ m^ of jointed and fractured rock and about 2 x 10^ m^ of snow and ice may have been partially fluidixed in the shaking that first dislodged snow and a small cirque glacier before a flood of rock rubble slid down all sides of a peak now called Shattered Peak. The avalanche lost half of its available energy in the first 30 sec of the 3.5 min avalanche, largely through sliding with high friction (p, = 0.60) down the surface of rupture. By this time, it was mechanic­ ally fluidized by the high kinetic energy of its clasts, and flowed in supercritical laminar flow as a complex Bingham plastic with a yield stress of 0.02 bar and with such high viscosities (1 x lO^poise for 7 0.02 < T < 0.1 bar and 4 x 10 poise for T S 0.1 bar) that it behaved largely as a thin flexible sheet, with deformation principally confined to shear at the base. It thus, essentially slid across a snow-covered, 2 gently sloping surface with low friction (|J. = 0.11) to cover 8.25 km of the ablation area of Sherman Glacier with an insulating blanket of ii rock debris that averages 1.65 m in thickness. Melting of ice in the area now covered by debris has been reduced to about 20 per cent of its pre-avalanche value, that ranged between -5 Mg m ^a ^ at about 420 m elevation, to about -8 Mg m ^a ^ at about 200 m. This has increased the net mass balance of the glacier from very negative to very slightly positive, largely as a result of two years of heavy winter snowfall (1964-65 and 1969-70) and of the mass of the avalanche with the 1963-64 winter snow preserved beneath it. Measured stratigraphie net balance at a point at about 430 m elevation on the glacier correlates almost perfectly with a function of selected climatological parameters (winter snowfall and temperature, and summer temperature) measured at nearby Cordova F.A.A. for the period from 1964 to 1971; this enables a 30-year record of net mass balance to be calculated. Correlation of a smoothed climatic record from Cordova F.A.A. with a smoothed record from Sitka Magnetic (at Sitka Alaska, 430 km southeast of Sherman Glacier) provides a 100-year record of net balance for glaciers in this region of coastal Alaska that is in excellent agreement with the known history of behavior of Sherman Glacier over the last three-quarters of a century. A study of flow of the glacier from 1964 to 1971 suggests that over this period, the glacier has responded only to changes in climate during the previous twenty years, and apparently has not yet responded to any effect of the earthquake, or of the rock avalanche. The debris apparently has slowed the rate of thinning of the debris-covered portion of the glacier, so that the effect of the avalanche to 1971 may have been only to slow or prevent changes that otherwise would have iii occurred. A review of the effect of debris on other glaciers shows that the glacier eventually will advance as a result of the avalanche. The predicted advance of about 630 m may not have begun until 1972 and should continue for about 50 years at a rate that will not exceed 20 m a IV Nothing can be more certain than the fact, so well stated by Charpentier in his 10th section, that the glacier does not owe its increase to the snow of avalanches, nor indeed to any snow which falls on the greater part of its surface. J.D. Forbes 4th letter on glaciers Edinburgh New Philosophical Journal January 1843 PREFACE After the great Alaska earthquake of 27 March 1964, President Johnson wrote: "It is important we learn as many lessons as possible from the disastrous Alaskan earthquake." More than 80 major rock avalanches fell during the earthquake, and most fell on glaciers, presenting and excellent opportunity to learn of rock avalanches, their mode of transport, and their effects on glaciers. In the years after the earthquake, many studies of them have been made, and many lessons learned. My studies at Sherman Glacier, in the Chugach Mountains of south-central Alaska, were not initially directed towards determining effects of the earthquake, although the continued monitoring of the glacier's response was a part of the work that I undertook. In 1969, I initiated a program of surface strain measure­ ment to determine the origin of a train of wave ogives at the base of a major icefall on Sherman Glacier. The program was ended abruptly in 1970 by a winter of record snowfall that left the ogive system still beneath more than 10 m of snow in late summer. My major efforts in that summer were redirected towards methods of evaluating mass balance of a glacier in which accumulation exceeded a measurable depth for available tools, and ablation in some areas was hidden from view beneath debris, and in others exceeded the limits of measurement (-11 m). VI This redirection of effort has led me to examine most closely the studies made by others of effects of debris covers on glaciers, and in turn, to examine the mechanism of emplacement of the debris cover on Sherman Glacier. In many areas of these examinations, I have found deficiencies in the earlier studies. Some of them I have overcome with my own observations, but many became apparent only after my field study had ended, and I have attempted to overcome them by reinterpreting the data of others, or by developing methods of estimation that make use of the limited available data. Beyond the many lessons learned of rock avalanches and their effects on glaciers, are the more important lessons taught by the failures of others: that each problem should be approached with-an open and enquiring mind that seeks, not to justify an existing model, but to improve the model, because each new event has new evidence to offer that leads to a better explanation of the processes involved; that few events are unique so that their temporal behavior can not be learned from the behavior of similar earlier events; and I have learned not to expect processes to perform miracles, nor to invoke processes that involve consequences inconsistent with the product. In all my work I have attempted to develop a product that I believe will stand as close an examination as I have given to the work of others but, as always, my facts are no better than Forbes' facts: they are consistent with my experience, and correct to the best of my knowledge.