IIIFカラー高解像度
国立情報学研究所 - ディジタル・シルクロード・プロジェクト
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| IIIFカラー高解像度 |
| Southern Tibet : vol.7 | |
| 南チベット : vol.7 |
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引用情報
THE PANGGONG-TSO.
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correctly says, becomes fresher as one goes eastward. The saltness denotes that the lake has no outlet. The supply of water comes mostly from glaciers. Some, he does not know how much, comes from the upper lakes through the channel at Ot. The information he got that the lake is frozen three months in winter is not correct, for only the upper, fresh, lakes freeze.
At i A, 3, and 7 feet he saw marks of higher levels of the lake. As to high beaches, his observations were confined to the southern side of the lake. At many places he found beaches at levels of from 4o to 5o feet above the present level of the water. Margin-marks occurred at various levels up to i oo or 120 feet.
He tries to trace the origin of the formations of Panggong-tso, mentions Trotter's maximum depth of 142 feet, and Godwin-Austen's finding the true cause of the lake to be the damming of its waters by side alluvial deposits.
Speaking of the N. W. corner he says: »Tracing on in this direction the highest margin-marks (those 1 oo or 120 feet) we find them to end against a fan, composed of gneiss, that comes out of a steep valley on the south-west, and abuts against the opposite (N. E.) hill boundary of our gorge ....» This then is what dammed the waters at the highest level to which we have traced them; it is the fan described by Godwin-Austen, and the place is Surtokh. There are other, lower, fans which at earlier periods may have been forming dams in the same way.
From this material Drew makes his deduction regarding the history of the formation of the lake. First a tributary of the Shayok went through the valley viâ Tankse. Then the fans were formed which dammed up the valley, and the lake came gradually into existence. Then followed a dry climatic period, the lake returned eastward, diminished and became salt. Drew believes that at levels below 5o feet the surface of the lake remained unchanged for longer periods than above 5o feet. Every one of the upper lakes in the Panggong-tso has, in his opinion, also been formed by fans.'
From our regions, south and north of the Kara-korum, Drew has some interesting observations.2 For Rupshu he prefers the term »high-level valleys» to that of plateau. Only farther north he finds the terms plateau and table-land correct. »Between the country which drains into the Shayok and that ,Those streams flow into the Karakash or into other rivers of Eastern Turkistan, is an elevated mass of ground-plains surrounded and crossed by rocky ridges — whence water finds no outlet, but dries up on the plains themselves.» He estimates the area of the isolated drainage-basin at no less than 7000 square miles. But he adds that »our knowledge of this tract is but scant, and of a portion of it only conjectural».
I This problem has in later years been dealt with by E. HUNTINGTON. Cf. Pangong : a glacial lake in the Tibetan plateau. Journal of Geology. Vol. 14, No. 7, 1906, PP. 599-617. 2 Op. cit., p. 331 et seq.
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