| | | | In the afternoon the wind increased to a storm, coming from S. 85° W. It was interesting to witness the impenetrable clouds of dust and sand which now again were driven along the ground. The whole landscape around at once was concealed, even the nearest hills to the east disappeared completely. It was like a desert storm in Takla-makan. The solid material was swept along the ice across the lake. Where the ice is uneven, forming small waves, some coarser material remains on the lee side and will cause some melting the next time the sun returns. At seasons when there is no ice, the storms must contribute very considerably to fill up the basin of the lake. We have already found how very shallow it is, and seeing these heaps of material, one is rather astonished that the whole basin is not quite filled up. As a rule, the situation of the isobaths, however, is explained by the transporting activity of the prevailing W. S. W. wind, for the deepest part of the lake is situated in its eastern half; the western being more directly exposed to the filling action of the wind. Remembering that this destructive transporting and filling activity goes on every year for thousands and hundreds of thousands of years, one is able to realize the result we find in the level forms and flat gradients of the Tibetan highlands. Nain Sing exaggerates the S. W. basin of the lake and makes it too broad. But as a matter of fact it is surprising that he has given the whole lake a form that is not very far from reality. This tells a good deal in favour of his capacity of observation. By passing only along one side of a lake, it is very difficult to draw even an approximately correct contour of its shore. This may easily be seen from Pan. I17A and I 17B, Tab. 21, where we seem to be surrounded by a ring of mountains, all of about the same altitude, only those to the N. E. and E. N. E., just behind our camp, seem to be higher on account of the short distance. The mountains south of us were called Tag-i-ak-lang-u. Our fourth sounding line goes W. S. W. across the lake and is I I km. in length. A long distance out from Camnp CI, the lake is so shallow that the ice is resting directly upon the black mud and ooze of the bottom, as may easily be seen in the openings of cracks. The cracks and crevasses, as a rule, run north and south, the long stripes of white salt, in the direction of the wind. Much of this salt is as if fixed to the ice, but still more is driven by the wind to the E. N. E., and out over the eastern plain. This action tends to decrease the salinity of the lake, as a certain amount of salt is carried away from the water in this way, every year. But on the other hand, the rainwater of the whole region finally flows into the lake, and takes a good deal of the windblown salt back to it. At any rate the salinity increases from year to year, though it is not yet strong enough to make animal and vegetable life impossible. The salinity also increases as the lake dwindles, as is readily visible from the beach-lines. |
IIIFカラー高解像度
