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National Institute of Informatics - Digital Silk Road Project
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| IIIF Color HighRes |
| Scientific Results of a Journey in Central Asia, 1899-1902 : vol.4 |
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Citation Information
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| THE LAKOR—TSO AND ITS BEACH—LINES. 167 | ||||||
| considered as the highest. This I ascribe to the fact, that it is situated lowest down in a part of the valley which has been relatively more exposed to erosion and inundation. At Camp CIX we found big expanses of gypsum and a number of strand-terraces; but these have been caused by more recent positions of the lake; yet even the lower part of the outlet of the Some-tsangpo valley, which issues just there, has a bay pointing towards the east. There was also another similar bay in the lower part of the thalweg of the river Lakor, and it has there left deposits of gypsum behind it. This last penetrated towards the south-south-east, and at the period in question this lake had a very extraordinary shape, in that it resembled a hand with outspread finger-like bays, or a star-fish with its arms radiating in every direction. The highest beach-line was thus formed at a time when the climate of Tibet was distinguished by its great constancy, and when the precipitation was so steady that the lake was subject to no fluctuations of level. Hence the wave-action, which both intrinsically and as a consequence of the greater extent of the lake, was able to engrave much deeper effects not only upon the hard rock, but also upon the disintegrated material of which the shelving acclivities are composed. If the slopes which at that period plunged down into the lake ever did bear signs of yet higher levels, they have since then been so long exposed to wind and weather that any such signs were completely obliterated before the lake began to fall in the constant way shown by the lower abrasion-lines. Add to this, that the great extent to which the lake then spread out, as indicated by the highest beach-line, is a proof, that the precipitation was at that time much more copious than it is now, and the direct erosive action playing upon the mountain-slopes was thus much greater, and this will in a measure have contributed to the destruction of any beach-lines that may have existed. All these things explain why above the highest beach-line we failed to discover any others of a similar character. Since that time the lake has dropped, though not with absolute regularity and uniformity; for had that been the case, the abrasion would at the most have only polished and smoothed the slopes, without leaving any beach-lines, or rather the successive abrasion terraces would imperceptibly have merged one into the other. The subsidence of level from the highest beach-line downwards took place relatively swiftly, so that there is an appreciable interval between that beach-line and its next highest neighbour. The latter is comparatively slight, and thus is indicative of a shorter continuance of level at that altitude. At the fourth line the lake would again appear to have maintained itself for a very long period of time. The beach-lines which come below that are all distinctly marked, though nothing like so energetically as at the highest stage and the fourth. The breach of continuity between the eight beach-lines to the left and the seven to the right has been caused by a hollow in the mountain-slope, in which erosion, and perhaps also avalanches of gravel, have produced more conspicuous effects. There exists one great and obvious difference between the eight upper beach-lines and the great number of others — we counted fifteen distinctly — which exist below them. The former are very prominent, the latter but faintly indicated, so faintly in fact that they can only be distinguished with difficulty. This proves that | |||||||
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