Short Title Changes in Surface Height, 1957-1967, Of
Total Page：16
File Type：pdf, Size：1020Kb
SHORT TITLE CHANGES IN SURFACE HEIGHT, 1957-1967, OF THE GILMAN GLACIER Keith Charles Arnold, Facu1ty of Graduate Studies, Interdiscip1inary G1acio1ogy, for degree of Master of Science ABSTRACT Keith Charles Arnold Determination of Changes of Surface Height, 1957 to 1967, of the Gi1man Glacier, Northern Ellesmere Island, Canada. Facu1ty of Graduate Studies Interdiscip1inary G1acio10gy Master of Science SUMMARY In 1967, 29 points on the Gi1man Glacier origina11y 10cated in 1957 were repositioned with a mean error of 0.36 m. Their height were redetermined with a mean error of 0.25 m. Refraction coefficients ranged from 0.047 to 0.558, with a mean of 0.162. A profile in the accumulation area showed 1itt1e change. Down glacier from a seismic profile near the average position of the equi1ibrium 1ine, 1957 to 1967, the average height 10ss was 2.4 m. From May 1958 to May 1967 the glacier advanced 25.4 m. A volume 10ss ca1cu1ated from height 10ss and glacier advance was 165 x 106 m3 , compared with 140 x 106 m3 ca1cu1ated from mass balance data, part1y estimated for missing years, and glacier f10w through the seismic profile. This area had a negative mass balance of 91 cm ice/yr; 69 cm ice/yr wou1d balance the vertical component of f10w, keeping the surface unchanged. DETERMINATION OF CHANGES OF SURFACE HEIGHT, 1957-1967, OF THE GILMAN GLACIER, NORTHERN ELLESMERE ISLAND, CANADA K. C. Arnold A thesis submitted in accordance with the regu1ations for the degree of Master of Science at McGi11 University. 1968 1 ® K.C. Arnold 1969 TABLE OF CONTENTS Chapter Preface i List of Figures ii List of Tables iH l INTRODUCTION 1 IUGG recommendationsfor recording the variations of existing glaciers 1 Definition of thesis problem 2 Phot'ogrammetric methods 3 Non-photogrammetrie methods 5 The problem of relocating fixed positions 6 The method of "repositioning" 7 Determination of the height of fixed positions 8 Description of the field area 8 II SURVEYING ON THE GILMAN GLACIER DURING THE IGY, 1957-1958 12 ·Choice of method 12 Errors of closure 13 Determination of glacier movement 15 III FIELD PROCEDURE, 1967 23 . IV ERRORS IN REPOSITIONING 26 Theory of errors in repositioning 26 Errors in repositioning encountered on the Gilman Glacier 29 V ERRORS IN DETERMINATION OF HEIGHTS 33 The problem of atmospheric refraction 33 VI CHANGES IN HEIGHT OBSERVED ON THE GILMAN GLACIER 42 VII DISCUSSION OF RESULTS 47 Factors affecting the change in level of a ~lacier surface 47 Factors observed or estimated on the Gilman Glacier 50 Changes in the snout of the Gilman Glacier 63 The change in volume down-glacier from seismic prof~le 101 66 VIII SUMMARY 70 REFERENCES 72 -i- PREFACE This thesis is based 011 field work carried out on the Gilman Glacier, Northern Ellesmere Island, during the International Geophysica1 Year, 1957 to 1958, and during the months of May and June, 1967. In 1957 and 1958 the work formed part of "Operation Hazen" organized by the Defence Research Board, Department of National Defence, Canada. In 1967 arrangements were made by the Department of Energy, Mines and Resources, In1and Waters Branch, for me to join a Defence Research Board field party revisiting the Gi1man Glacier. l wou1d 1ike to acknow1edge the great assistance extended by Dr. G. Hatters1ey-Smith, for making it possible for me to visit the Gilman Glacier in 1957, 1958 and 1967, and for a110wing me to use unpub1ished field data from the most recent visite The 1967 work wou1d not have been possible without the carefu1 surveying observations of F/Lt. C. D. Drew and F/Lt. P. G. Pinney of the Royal Air Force Ellesmere Island Expedition, 1967, and assistance in the field from u. Embacher and J. van der Leeden. l wou1d a1so 1ike to thank my employer, the Department of Energy, Mines and Resources, for educationa1 1eave during the winter of 1967-68, for a110wing time for the preparation of this thesis, and for assistance in typing and drafting diagrams. Fina11y l would 1ike to thank my supervisor Dr. Fritz Muller" for his academic supervision, and for his encouragement to me whi1e writing this thesis. -ii- LIST OF FIGURES Figure 1 Location of field area Il 2 Control surveys for geophysica1 work, International Geophysica1 Year, 1957-1958 17 3 Location of seismic and gravity profiles, 1957-1958 18 4 Glacier movement determined over one year, 1957-1958 20 5 Glacier movement determined during the summer of 1958 22 6 Error figure for repositioning 28 7 Ca1cu1ation of coefficient of refraction, k 34 8 Location of height changes measured in 1967 41 9 Amount of change of surface height, 1957-1967 43 10 Long profile of the Gilman Glacier 46 Il Effect of a wave type perturbation of f10w on change of surface height 49 12 Me1t re1ated to accumu1ated me1ting degree-days 54 13 Comparison of mean dai1y temperature at A1ert and Gilman Glacier, 1957-1958 56 14 Comparison of 142 mean dai1y temperatures, A1ert and Gilman Glacier camp, 1957-1958 (Median Values) 57 15 Relation between mass balance and change in thickness, 1957 to 1967 62 -iii- LIST OF TABLES Table 1 Glacier movement determined over one year, 1957-1958 19 2 Glacier movement determined during the summer of 1958 21 3 Maximum errors in repositioning (m) for an angu1ar error of 10" arc in directions 29 4 Distribution of errors of directions to repositioned points 30 5 Distribution of distances to repositioned points 30 6 Distribution of errors of horizontal coordinates of repositioned points 31 7 Accuracy of repositioned points on the Gi1man Glacier 32 8 The advantage of simu1taneous reciproca1 vertical angles 36 9 Accuracy of height changes measured on the Gi1man Glacier 40 10 Summary of changes of surface height on the long profile of the Gilman Glacier 44 11 Net accumulation for the Gilman Glacier, and precipitation data for A1ert 51 12 Me1ting degree-days at the Gilman Glacier, estimated from A1ert mean dai1y temperatures by comparison of individua1 values 55 13 Me1ting degree-days at the Gilman Glacier, estimated from A1ert mean dai1y temperatures by modified 1apse rate method 58 14 Observed and estimated mass balance on the long profile of the Gilman Glacier (ice equiva1ents) 60 15 Distance of the snout of the Gi1man Glacier from West Base cairn 64 -~ cruœTm l INTRODUCTION IUGG recommendations for recording the variations of existing glaciers It has long been realized that glaciers undergo changes in their extent and thickness, and that these changes are related to changes in seasonal snowfalls and summer warmth. Because of the complicated physical character of ice ·as a material in nature, the response of any individual glacier to locally measured climatic changes is not simple, and is still a matter for theoretical investigations, to be checked by field observations. In spite of this difficulty it is hoped that a large sample of glacier changes on a world-wide basis will be valuable for increasing our understanding of the glacier-climate re lationship, and of extending our knowledge of climatic change in glaciated areas into the past, finally attaining the ability to pre dict the effect of a small climatic deterioration in a glacierized area. During the General Assembly of the International Association of Scientific Hydrology held in Helsinkiin 1960, the Commission of Snow and Ice resolved to undertake the recording of variations of existing glaciers on a permanent basis (General Assembly of Helsinki, 1960, p. 5). In particular, they agreed to prepare a document detailing the types of measurement desirable. A Sub-Committee was set up to prepare this report, which was published in the proceedings of the Obergurgl Symposium of the IASH, he Id in September, 1962, (Symposium of Obergurgl, 1962, pp. 306-309). With minor modifications, this report was adopted as a basis for recording glacier variations during the International Hydrological Decade, in IHD Resolution 1-13 (Kasser, 1967, p. 47). -2- The report of the Sub-Committee on Variations of Existing Glaciers to the Commission of Snow and Ice stressed the glacier-c1imate re1ation ship as the under1ying reason for recording glacier variations, and p1aced particu1ar importance on the desirabi1ity of having the greatest number of reasonab1y simple measurements of glacier variations, rather than a more 1imited number of high1y sophisticated measurements. It was desirab1e that measurements made during the International Geo physica1 Year shou1d be incorporated in the series, and according1y a five year interva1 of measurements commencing in 1963, five years after the close of the I.G.Y., was suggested. As balance measurements on a glacier are norma11y referred to the time of minimal seasona1 snow cover, the measurements for glacier variations shou1d, if possible, be made at the same time. The body of the recommendations of the Sub-Committee was divided into two sections, the first dea1ing with basic observations necessary for recording the variations of a glacier, and the second dea1ing with more comprehensive measurements (Symposium of Obergurg1, 1962, pp. 307-308). The basic observations suggested were a genera1 description of the glacier and its situation, photographs of the snout from fixed reference stations and measurements to estab1ish the position of the snout, the measurement of the height of the snow 1ine, and measurement of surface heights at se1ected points. Definition of thesis prob1em The latter prob1em, the measurement of changes of surface height at se1ected points, forms the subject of this thesis. A method was chosen that is suitab1e for sma11 parties without access to photo grammetric equipment, and was app1ied to an Arctic glacier origina11y -3- studied during the International Geophysical Year.