Den glaciala, premarina utvecklingen inom den senkvartära Viskafjordens sidodalar

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Abstract
This paper contains the results of an investigation of the systems of ice-dammed lakes, which occupied, in Late-Glacial time, the terrain on either side of the ancient Viskan Fiord in the SW part of the province of Västergötland. Topographically, three kinds of such lakes are distinguished: 1) nunatak lakes, 2) local marginal lakes, and 3) marginal lakes of regional extension. No wide waters seem to have been formed above the marine limit during tho melting away of the land ice from these parts, rests of ice filling the central portions of the branches of the Viskan valley until its final disappearing at the ingression of the sea, for no sediments of such waters are discovered. The marine limit of the ancient fiord and its branches is situated at about 70–90 m above the present sea level, falling gradually towards SW from the inner parts. The beaches of the first nunatak lakes appear at 180 m, on Mt Gallåsen, and 203 m, on Mt Hokåsen. Below these heights there follow a great many nunatak lake beaches and such of local and regional marginal lakes, the lowest of which emptied themselves into the marine fiord. Sloping drainage channels, eroded at the ice margins by outflow of water from the dwindling ice, occur at every height above the marine limit. Very often they end at the ancient shore of an ice-dammed lake. The lowermost ones discharged into the sea at the marine limit, thus affirming the beach in question to indicate the highest stand of the sea. The occurrence of marginal drainage channels at the uppermost nunatak lakes reveals the ice to have been climatically dead even at this stage. Dynamically, however, it remained active almost till the final disappearing of the lumps on tho bottom of the deeper valleys, into which it eventually broke up. This latter fact is proved by scattered terminal moraines and drumlins, indicating downward movement of the valley ices. But ablation moraine, deposited from ices that were dead even dynamically, also occurs. The different systems of ice-dammed lakes are correlated chronologically by means of the gradients of their shore levels. By connecting the heights of lakes, thus proved contemporaneous, the general sloping of the ice surface is conjectured. At the stage of the first nunatak lakes it sloped towards SW roughly 0.35 m per 100 and, towards the end of the melting period, at the utmost 0.2 m per 100. Furthermore, the gradients disclose three discontinuities in the land upheaval, probably corresponding to those discerned by von Post in the epeirogenetic development of Halland in Gothi-Glacial and Fini-Glacial time.

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