A STORM ON THE LAKE. 49
10.0 m. The maximum depth of the lake, therefore, remains unknown, though, judging from a diagram of the soundings taken, the depth hardly can be more than 8o m. Still this lake proved to be the deepest of all I had sounded in Tibet. As a rule the Tibetan lakes are very shallow as could be expected from the general morphology of the plateau-land. But the relief of the surroundings of Lake L2 -laten, with high, steep mountains, especially at its southern side, is responsible for the comparatively great depth of this basin.
The distance across the lake had been measured every seven or eight minutes with an instrument for taking the velocity of currents constructed by Lyth, Stockholm. A steep terrace, at the most 5 m. high, followed the southern shore, but in front of it was a long, narrow lagoon separated from the lake by a pier of gravel, 1 m. high. This form of shore seemed to continue for miles towards the east. In the morning the lagoon at the northern shore had been covered with ice, 1 cm. thick. At the southern shore the water of the lake had a temperature of 9.9°. The freezing of the lakes, though at a very moderate rate, therefore may be said to set in about September 20th. At Camp XV we had had a belt of thin ice 2 m. broad along the western shore. This belt slowly increases in breadth and thickness towards the middle of the lake in the course of the autumn. But a lake of this depth will probably not be frozen all over before the middle or end of November, and perhaps still later.
From the point where we had landed, we steered E. N. E. and east with the intention of reaching the eastern shore where the caravan had orders to pitch Camp XVII. During this crossing of the lake we were attacked by a very severe western storm, which made all observations absolutely impossible. A few minutes before the strong wind began I got a new illustration of the transport of solid material by the wind. Above the transverse threshold in the west, yellow and light brownish clouds rose in the air to an altitude which seemed to be about 3o°. These clouds of sand and dust were darker near the surface of the earth and became lighter the higher up they reached. After some minutes more the outlines of the mountains began to disappear, and finally vanished completely. There is no doubt, therefore, that these clouds of dust are carried away for great distances. Perhaps they are brought all over and beyond the lake. In the boat one could not notice any dust in the air. Only twice or thrice at the beginning of the storm I was able to take the velocity. The distance of 23 km. to the eastern shore may, therefore, only be considered an estimate. We were driven by wind and waves for nearly two hours. The flat belt of land along the northern shore, where Wellby and Malcolm had wandered I o years earlier, seemed to run out in rounded necks of land inside of which lagoons were situated. The latter could only be seen when their piers were pierced by narrow channels. At the eastern shore there was a rounded terrace of
7. IV.
IIIFカラー高解像度
