IIIF Color HighRes
National Institute of Informatics - Digital Silk Road Project
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| IIIF Color HighRes |
| Southern Tibet : vol.7 |
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Citation Information
530
THE OLD DRAINAGE OF THE SELLING-TSO - PANGGONG-TSO DEPRESSION.
was of course that the affluents in the upper part of the Tso-ngombo dwindled to mere brooks; a consequence of the increasing desiccation.
In the same way the upper courses of the westerly flowing rivers which once crossed the interior of Tibet were disturbed by the differential movements of the ground in their valleys, interrupted and forced to feed self-contained lakes which in time became salt. In some cases such lakes may have had outlets across rising thresholds, but were finally completely isolated. In other cases parts of a river flowing west may have been forced to flow eastwards.
On p. 500 I have mentioned some of the self-contained lakes on the depression line between Selling-tso and Panggong-tso. In the following list I have entered 18 points on the same line, not all of them being lakes. The altitudes of i 2 of these points have been determined by me, 4 by LITTLEDALE, one by DEASY and one by NAIN SING. The last mentioned Pamar-tso, has in the list 4350 m., as Nain Sing's
m. are certainly too low. Turgu-tso is determined by Deasy, Tsemar and the next by Littledale.
4191 three
Selling-tso
Chargut-tso
Addan-tso
Dagtse-tso
Tongka-tso
Pamar-tso
Oman-tso
Lagoon (E. of Jim-tso)
Jim-tso
4454 m•
))
4611
4615
4615
4544
4500 »
4350
4507 4458 4495
))
»
n
»
»
Camp CXVIII
Tsolla-ring-tso 4440 »
Camp CXX 4406 »
Turgu-tso 4340 »
Tsemar 4636 »
Rawang 4339 »
Dojur-tso 4355 »
Roksum 4371 »
Panggong-tso 4317 »
All these points are situated on a line which is slightly bowed towards the south, and parallel with the general stretching of the mountain ranges to the north and south of it, and also with the Transhimalayan and Himalayan systems.
It is a striking feature of this list that the absolute altitudes of the depressions as a rule become lower from east to west. Selling-tso is nearly 30o m. higher than Panggong-tso, and the whole valley gradually slopes westward. The exceptions to this rule may be regarded as the results of the differential movements of the crust. The slope is extremely slow. If the distance from the mouth of Sachu-tsangpo in Selling-tso to the eastern end of Tso-ngombo is 930 km., and the difference in altitude 294 m., then the rate of fall will be only 1:3163. But adding the length of Panggong-tso and of the Drugub river, the length of the valley will be II o8 km., the difference in altitude 737 m., and the rate of fall I:1503. And adding the lowest part of Sachu-tsangpo from the point where I crossed it in 190 I , which is 150 km. from the mouth of the river in Selling-tso, the distance becomes 1258 km., the
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