The Assam Earthquake of 1950

Abstract

In january 1950 my wife and I left the Tocklai Tea Research Station in Upper Assam by road, on a journey up the Lohit valley. For the last two years Tocklai had been our base for plant hunting expeditions south of the Brahmaputra, including Manipur and the Mishmi hills. The last named is, for the botanist, perhaps the most fascinating, because the least explored, region in the whole of India; and the prospect of eight or ten months botanizing in the very heart of the mountains behind the Mishmi hills was alluring. It is not my purpose to describe in detail either the wonderful vegetation, or the fascinating glacial history of this region. But in order to make the short term?and probable long term?effects of the great earthquake of 15 August 1950 intelligible, it will be necessary to give a brief description of the upper Lohit valley. Between the point where the Lohit leaves the hills, and Rima (a distance of about 125 miles), eight major tributaries are crossed, the three largest being the Tidding, the Delei, and the Dav?all rising in the northern Mishmi Hills. As these hills are comparatively high (many of the peaks exceed 15,000 feet), and lie close to the plains, they catch the full force of the summer monsoon, converging on to them through the funnel-shaped Assam valley. The result is a rainfall heavy everywhere, and in some places (Denning, for example) exceeding 200 inches. Nor is that all. Their position, wedged between the escarpment of the Tibet plateau to the north-west and the Yunnan plateau to the east?both these areas, be it noted, dry in winter? draws all the moisture of the north-east monsoon on to themselves, so that the snowfall is also severe. The result is a heavy snow melt in the spring which, when combined with heavy spring and summer rain, causes tremendous erosion, particularly at the higher levels, before the vegetation has started into growth. On the left bank only five large tributaries enter the Lohit, three of which rise on the Dapha Bum range close to the Burma frontier. At Minzong the Ghalum river joins in from the south-east. Seen from the west, its valley has all the appearance of being the main valley, whose direction it continues?as, indeed, it may formerly have been, when the present main valley to the north was blocked by ice. Evidence pointing to the same conclusion is found in a north-south alignment of high peaks immediately west of the Minzong bend, with Dapha Bum (15,020 feet) south of the river, and an unnamed peak of 17,172 feet about 25 miles to the north. The eastern flank of this range was heavily glaciated and fed the Lohit glacier, while from its western flank flowed the lower Lohit. The joining up of the glacier stream with the Ghalum at Minzong came later. All the larger north bank tributaries are spanned by wire rope suspension bridges, and though the cables of the Delei bridge had sagged badly, the bridge was quite safe. Even before reaching the Delei, the road engineers