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Transport conditions of mountain-surging glaciers as recorded in the micromorphology of quartz grains (Medvezhiy Glacier, West Pamir)

Muzińska A.

Geologos

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2015

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Vol. 21, No. 2

127--138

EN

In order to reproduce the conditions under which sediments were transported in surging glaciers, samples were taken from the margin and foreland of the surge Medvezhiy Glacier situated in West Pamir (Tajikistan). They were subjected to an analysis of rounding and frosting of quartz sand grains (0.8–1.0 mm) and of grain surface micromorphology under scanning electron microscope (SEM). Results obtained showed intense chemical weathering occurred in the majority of quartz grain surfaces, marked in the form of etching and precipitation. Frequencies of microstructures of glacial origin were low; individual microstructures were visible on single grains. A predominance of the crushing process over abrasion in transformation of quartz grains was noted. The commonest microstructures connected with a surge-glacier environment were large and small conchoidal fractures. However, grains with primary features not connected with a glacial environment were equally common. The majority of the grains examined showed features of multiple cycles of mechanical and chemical weathering forming a microtexture under various conditions (overprinting). Common features of grains from surging glaciers are also breakage blocks of >10μm, which depend of the phase of separation of the grain from the rock or on thermal changes in the glacier’s foreland.

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Geologiczne uwarunkowania dynamiki procesów brzegowych rzek zachodniego Podhala

Augustowski K., Chmielowska D., Kukulak J.

Przegląd Geologiczny

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2013

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Vol. 61, nr 12

755–-763

EN

The western part of Podhale region is drained by the Czarny Dunajec and the Biały Dunajec rivers, flowing from the Tatra Mts., and streams originating in the region (Cichy Stream, Bystry Stream, Czerwony Stream, Wielki Rogoźnik). River banks are cut in the Podhale Flysch or in the alluvium of these rivers overlain with loam deposits of varied origin. This paper investigates the combined effect of weathering, frost processes and mass movements on the banks of the Czarny Dunajec River and its tributaries typified by different substrate material. Bank retreat due to frost processes was measured during multigelation periods using erosion pins. Grain size distribution and cohesion of the substrate were also determined for alluvial and loam deposits. On flysch cutbanks, we determined joint spacing and the density and direction of fractures, and other structural and textural characteristics of the rocks. The results indicate that the rate of bank retreat decreases from the banks cut in sandy loam deposits, through alluvial loam banks (with high clay content), the banks composed of poorly cemented gravels and shaly flysch, to the banks cut in sandstones and highly cemented Neogene gravels. Bank retreat due to frost processes and mass-wasting was more efficient in the cold half-year.

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Frost weathering of selected Tatra rocks in the light of laboratory tests

Lubera Ewa, Krzemień Kazimierz, Krzaklewski Paweł

Studia Geomorphologica Carpatho-Balcanica

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2022/2023

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Vol. 56/57

5--29

EN

Frost weathering is one of the types of physical weathering. The goal of this study was to find out how the rates and ways of frost weathering vary, based on laboratory research studies. A variety of types of Tatra rocks, their mineral composition, degree of fissuring, various capabilities of absorption of water, and porosity, all determine the progress of the process of weathering as well as its dissimilar effects and products. Generally, the breaking apart and gradual disintegration of rock into smaller fragments are the results of weathering. Rock samples, intended to be studied in the laboratory, represented rock formations of different age and various geologic units of the Western Tatra Mountains. The laboratory research studies that were conducted simulated processes occurring under natural conditions, which allowed performing an analysis of the physical properties of rocks. The rocks of the greatest and the smallest resistance to frost weathering were identified based on a calculated frost weathering index. The significant resistance of the studied Tatra rocks is influenced by their low open porosity, low capability of absorption of water, rock toughness, high degree of sorting of rock grains (grain sizes are similar), low degree of fracturing of samples in their initial state, and the presence of cementing material filling in rock pores almost entirely. The influence of texture on the disintegration of rocks was not observed, whereas the presence of mineral veins in rocks determined the way they fell apart, which occurred in samples of fine-grained conglomerate.