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
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| THE MOUNTAIN RANGES AND THE PRECIPITATION. | 5I7 | |||||||
| Remembering the Kailas and other ice and snow-covered mountains north of the Satlej lakes, and the Gurla-mandata, Ganglung-gangri and Kubi-gangri south of them, we find that these lakes are situated between incomparably higher and mightier mountain ranges than the Hwang-ho lakes. In spite of this fact thé Satlej lakes have reached a more advanced stage of maturity in the cycle of their development than the Jarin-nor and Orin-nor. Neither the absolute altitude of the lakes which in the case of the Manasarovar and Rakas-tal is 350 m. higher than in the case of the Hwang-ho lakes, nor the absolute height, compactness and snow and ice covering of the surrounding mountains therefore seems to be the most important factor in the preservation of the hydrographical functions of the lakes in question. It would seem that those lakes which are situated at the foot of the mightiest and most snow-and ice-covered mountains, would be more abundantly fed by affluents, but as a matter of fact the lakes at the foot of the lower mountains obviously receive more affluents and therefore preserve their hydrographic functions in full activity. There must exist some other factor that brings about this state of things. The outlines and the forms of the two pairs of lakes make it very unlikely that their depressions could ever have been excavated by glaciers. Nor are there any moraines or talus fans from tributary valleys which have dammed them up. Their creation must therefore needs be due to the secular and differential movements in the earth's crust which are so intimately connected with the rise of the mountains. As the latter proceed, small thresholds and ramifications in the latitudinal valleys may easily take part in the general elevation of the main ranges, and in this way relatively low depressions may be left alone behind the uplifted parts of the valleys. In the course of time the cavities may increase in size, and, provided the precipitation is sufficient, they will not only become filled with water, but the superfluous water will also seek an outlet across the uplifted threshold and cut its bed deeper and deeper by its erosive power. Provided that the cycle of development in the instances of the two pairs of lakes has been of the sort set forth above, the only conclusion we can draw is that the difference in their present state must be due to the distribution of precipitation. And here the part played by the absolute altitudes and the massiveness of the surrounding mountains comes in. In spite of the fact that the Hwang-ho lakes are situated four and a half times as far from the lowlands of the Ganges and Brahmaputra as the Satlej lakes, the latter receive less water from the surrounding moun- tains. The gigantic mountain ranges rising to the south of the Satlej lakes catch the greatest part of the moisture of the south-west monsoon which, in the form of rivers, returns to the south to the Ganges, while the cavities of the lakes remain comparatively dry on the lee-side. The basins of the Hwang-ho lakes, on the other hand, being surrounded by comparatively lower ranges, are more exposed to the moisture of the winds, whether from the south-west or from the Pacific. | ||||||||
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