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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
•i
M,
THE WESTERN PANGGONG-TSO.
345
I will now touch briefly upon the observations that I made with regard to the relations existing between the Panggong-tso and the drainage-area of the Indus, but only briefly, because my journey to Leh was too hurried to admit of my taking extended observations. I had thus ascertained that the lake-system of the Tso-ngombo and Panggong-tso is as a whole limited on the east by the gently ascending plateau country, bordered on north and south by gigantic mountain-ranges, and in the west possesses no more emphatic line of demarcation than the low sill or threshold to which I have alluded, and which in its longer cross-section presents the appearance shown in fig. 269. If a not very
deep gap were to be cut through this barrier, the lakes would secure an outlet to the west, and would empty their surplus water into the Indus. With regard to the height of this threshold above sea-level, I am unable to make any satisfactory statement. According to the reading of my aneroids, compared with those of the boiling-point thermometers, it ought to be 4327 m. ; but before we can use this datum as a basis for safe conclusions, the exact value ought to be accurately known. I have mentioned above the existence of a strand-terrace at an altitude of 54 m. above the lake. When the basin was filled up to that level, it had of course an outflow towards the west over the top of the low sill, and the altitude of the latter above the level of the lake is at the present time perhaps the same, or only a little lower than, the altitude of the terrace, although the aneroid reading gives it a height of only i o m. above the lake. Once, but at a very distant epoch, the lake received such copious supplies of water that the efferent stream to which they gave rise was a large river. The circumstance that this left behind it no erosion terraces in the neighbourhood of the little threshold pass does not necessarily prove very much, because the bottom of the valley has since that epoch been levelled down by the progressive denudation. Moreover the efferent stream was possibly so powerful that it occupied the greater part of the width of the valley. Since the climate grew drier, the volume in this efferent stream has also grown less, and during this period erosion terraces will in any case have been formed in the bottom of the valley. Finally the drop in the level of the Panggong-tso has proceeded so far, and advanced at such a rapid rate, that the erosive energy of the outgoing stream was not able to keep pace with it; for had it done so, it would have been able to carve a passage for itself down through the threshold barrier, and to-day the Panggong-tso would still possess an outlet just as the Tso-ngombo does. But this is not the case. The Panggong-tso has become cut off, and now forms a self-contained salt-lake, which does not receive sufficient inflow water to compensate for the loss through evaporation.
Hedin, Tourney in Central Asia. III'. 44
Fig. 269.
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