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Hinkel, K.M., 1986

Palsa formation in north-central Alaska

Bibliographic Reference

Hinkel, K.M., 1986, Palsa formation in north-central Alaska: University of Michigan, Ann Arbor, Ph.D. dissertation, 200 p., illust., maps.

Abstract

Four processes have previously been identified as possible aggradational palsa growth mechanisms. Palsas can be initiated and maintained by ice segregation, hydrostatic pressure, elevation-induced hydraulic pressure, or buoyancy. Each of these pure end-member processes can be conceptually linked to a unique set of ice textures, fabrics, and stratigraphy in the palsa core. In addition, the ionic concentration pattern with increasing depth, as measured by the equivalent electrolytic conductivity of the melted ice, can be used to estimate if the system was hydrologically opened or closed at the time of fusion. Field data indicate that massive ice formed in an open system increases in purity with depth, presumably in response to the slower rate of ice crystallization associated with reduced thermal gradients. Conversely, data obtained from closed-system freezing experiments show an initially decreasing, then increasing bulk ionic concentration pattern toward the unfrozen core. A simple model indicates that this pattern reflects the effects of continuous liquid enrichment resulting from the rejection of ions from the selective ice lattice. The glaciological characteristics associated with each palsa growth mechanism were used to classify the growth history of ice mounds at three sites in North-Central Alaska. In a stream valley bog near Slope Mountain, a massive ice plateau more than 1 m thick is formed annually by the concordant injection of water in a hydrologically constricted system. The glaciological characteristics of ice-cored mounds located at the quiescent margin of the bog indicates that these mounds are preserved remnants of a previous massive ice plateau, which have been protected from ablation by a 30-cm thick organic mat. These stable features are identified as degradation palsas. At Toolik Lake and Sukakpak Mountain, palsas appear to form in response to hydrostatic pressures generated in hydrologically closed systems. The location of these features is largely determined by site-specific factors. However, some mounds are clearly associated with road berms, indicating that the berm acts as barrier to subsurface hydraulic flow. In addition, small mounds formed by the hydrostatic pressure, buoyancy or ice segregation mechanism were identified on the basis of core characteristics.

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