Dynamiczne procesy glacjalne na południowym Spitzbergenie : w świetle badań fotointerpretacyjnych i fotogrametrycznych

Abstract

This monograph presents results of research carried out using terrestrial photogrammetry over the period 1982—1985 and photointerpretation of aerial pictures taken in 1936, 1960 and 1961. Archival topographic maps and photogrammetric surveys have also been used. The state of the glaciers in South Spitsbergen has been examined (chapter 3). The analysis includes morphological type (tab. 1) and morphometric features (tab. 2). Based upon aerial photos taken in 1961 (fig. 7) the glacial zones, thermal regime have distinctly reduced volume over the period 1936—1961 (chapter 4, tab. 3). The diagram of changes in glacier thickness with the altitude shows the existence of kinematic waves (fig. 20—24), which in the case of Finsterwalderbreen, are the result of a surge. Werenskioldbreen, which terminates on land (chapter 5), and a grounded tidewater glacier Hansbreen (chapter 6) have been taken as examples to investigate glacier movement. A close relation between surface velocity and the amount of melt water flowing to the glacier bed (fig. 40—42) is observed. It supports the important role of basal slip for the glaciers of Spitsbergen. Maximum flow velocity is observed in mid-July, the first part of the ablation season (fig. 44 and 45). For land-terminated glaciers internal deformation is the dominant flow mechanism, accounting for more than 60% of the mean annual flow. Basal sliding decreases near the front. In the case of tidewater glaciers, basal sliding increases toward the front (at the terminus of Hansbreen 95% of surface velocity results from basal slip). Compressional flow dominates in the frontal part of glaciers terminated on land. Near the front of Werenskioldbreen, velocity vectors are emergent and velocity decreases gradually toward to the terminus. Current dynamics of Werenskioldbreen resemble the quiescent phase of a surging glacier. Movement of the frontal part of tidewater glaciers is tensional. Directions of Hansbreen flow vectors projected on a vertical plane are parallel to the surface and only close to the terminal cliff do they dip seaward. In this work special attention is paid to ablation by calving of tidewater glaciers (chapter 6). An annual cycle of Hansbreen calving activity and the relations between calving and glacier seismicity have been examined. The mechanism of calving of the Spitsbergen grounded tidewater glaciers resembles landslide slumps. Calving results from tensional movement with postive feedback such as the „Jakobshavn effect (Hughes, 1986) accelerating the movement. Underwater melting has also been calculated; it is responsible for about 20% of calving speed. Data from Hansbreen (Jani a, 1982, 1986, 1987b), Kongsvegen (Voigt. 1979), Alaska tidewater glaciers (Bro w n and others, 1982, table 1) make it possible to formulate a „gentral calving law”: Vc = k+f(V9) where calving speed Vc is a function of glacier velocity V9; a calving coefficient k depends on climatic conditions. Preliminary results suggest that the function f(V9) is linear. For tidewater glaciers on Spitsbergen, calving typically accounts for 25% of the mass loss. Fluctuations of the fronts of the South Spitsbergen glaciers have also been investigated (chapter 7). Recession rates of tidewater glaciers depend mainly on the sea depth at the glacier terminus. Since the beginning of this century the surface of the Hornsund tidewater glaciers has decreased by 88 km2, yielding a mean deglaciation rate exceeding 1 km2 per year. Analysis of surface features of the glaciers of South Spitsbergen proves that most of them are of surge type (chapter 8, phot. 14—20). Observations of the dynamics and geometry changes of Spisbergen glaciers together with recent results from Alaska (K a m b and others, 1986) and the Alps (I k e n and Bindschadler, 1986) suggest that the superposition of kinematic waves at different scales can trigger a surge. The importance of changes in the subglacial drainage structure has been taken into account. A simplified model of surge-type glacier evolution caused by climate warming (decreasing glacier volume and increasing melt water flow to the bed) is also presented (fig. 63). Some gemorphological consequences of the dynamics of contemporary glaciers have been considered (chapter 9). Formation of ice-cored frontal moraines and push moraines must be treated as an effect of rapid glacier movement typical of the active phase of surging. Seasonal oscillations of the terminal position of tidewater glaciers cause annual push moraine ridges that the a typical feature formed during the quiescent phase of surging. For the marine environment, the active phase is associated with superimosed push glacial-marine deposits of great thickness. In the final part of this monograph the usefulness of photo-methods in glaciology is evaluated. Lastly, the intensity of glacial processes in South Spitsbergen is compared with that in other Arctic and Subarctic areas.