That a glacier carves a ‘U’ shaped valley, is elementary geography. But when such a valley becomes a narrow ‘V’ shaped valley abruptly, it is perplexing.

Shalang Glacier, a part of Gori Ganga basin in the Central Himalayas of Uttarakhand has this feature that motivated R K Pant of Physical Research Institute (PRL), Ahmedabad and his fellow researchers from Indian Institute of Geomagnetism (IIGM), Mumbai to brave the freezing temperatures of the glacier and explore the region.

It is also known that the glaciers preserve the evidences of the past climates, but here it was something much more. They came across some interesting evidence about the earthquakes that must have rocked the frozen terrain in the pre-historic days.

The Quaternary or the last chapter of the earth’s history started about 1.75 million years ago (Ma). The older part of the chapter is the Pleistocene, the period of Ice ages and the Holocene which started some 10,000 years ago and continues even today, is a period of warmth.

With the help of the available evidences Pant and his colleagues were able to work out the glacial history and past climates and also the impact of Trans Himadri Fault (THF) on the late Quaternary glaciation processes.
But while reconstructing the past that too in terms of thousands or millions of years for a geologist, the evidences are vague. For example, Pant and his colleagues knew that a glacial valley is ‘U’ shaped. But why the valley of Shalang Glacier abruptly terminated northwest of Rilkot near a straight course of Goriganga River was inexplicable.

Rivers normally seldom flow along a straight course. They rather follow a sinuous course. They found that the Trans Himadri Fault ran parallel to the river course or in other words it was THF that guided the course of the river in that part.

This fault runs parallel to the Goriganga (northwest-southeast) till Martoli and then turns in northwest direction. Trans Himadri Fault contained the glacier in the northwest part only, as confirmed by the typical ‘U’ shaped valley and the southeastern part was a river valley confirmed by the ‘V’ shaped valley.

Pant and his colleagues have actually confirmed that the THF which was till recently considered active; till 11 Ma, that is till late Miocene period of the Earth’s chronological history. It has been active even in the last chapter that is Quaternary. Incidentally the present day activities are part of this chapter only.

Using Radiometric dating methods they found that even in Gangotri glacier the valley glaciation was active till about 64 Ka. Similarly in Garbyang they found evidence that led them to conclude that it was an active THF that cut the glacial regime and many times caused lakes to be formed and also created deep gorges close to glacial valleys.

In Garbyang they succeeded in getting optical luminescence dates of lake sediments and glacial gravels which indicated three major tectonic events during 22-17 ka, 14-13 ka and <11 ka.

Fault movements, as per the seismologists, have been behind some of the great earthquakes. In other words as late as nearly 11,000 years ago, the higher Himalayan was being rocked by earthquakes that re-carved the topography, caused the glaciers to abruptly halt and also influenced the climate.

If such huge earthquakes have rocked the Himalayas in the past can we rule them out for the future? It will not be prudent to rule out the possibilities of a high magnitude earthquake in the Himalayas. While it is not possible to stop development activities, precautions against possible disasters have to be inbuilt in the structures that come up.