On February 7, a flash flood hurtled down in Chamoli, Uttarakhand killing at least 31 and destroying two hydropower projects. The trigger for the floods is believed to be either a glacial lake being breached or a broken mountain peak falling on a glacier. Scientists from the Wadia Institute of Himalayan Geology (WIHG), Dehradun were among the first teams of experts to leave for an examination of the causes of the disaster. Kalachand Sain , Director, WIHG, says in an interview to The Hindu’s Jacob Koshy, that it was large rock falling on a hanging glacier that precipitated the avalanche and flood. He also highlighted the challenges of accessing the glacier because of which it could be months before the exact cause that triggered the rockfall could be determined.
The Wadia Institute has sent a team of scientists to explore the causes of the flash flood. What have they found so far?
A team of five immediately left for the spot. They have made some measurements of the topography near the locations but access is difficult. They also undertook an aerial survey. What we know so far is almost entirely based on an analysis of satellite imagery, with some ground observations. Ground-based measurements are critical to supplement this but the prevailing conditions aren’t conducive. These are glaciers at an elevation of 5,000-6,000 metres. Himachal Pradesh has 10,000 glaciers, Uttarakhand has 1,000 glaciers — and all are in extremely inhospitable locations. Normally, access to these regions is only possible in the summer, and it’s not easy even then. That’s why our knowledge of glaciers is limited and this is inadequate. That makes satellite analysis or aerial surveys critical but they have their limitations.
What does your preliminary analysis suggest?
We are about 90% certain that this was caused by a combination of a large piece of rock, possibly from a mountain peak, breaking off. This was probably part of the Raunthi/Mrigudhani mountain. It fell on a hanging glacier, probably perched off a cliff. The impact from the falling rock broke it [the glacier] and this mass of rock and ice debris avalanched over a nearly 40 degree slope for two kilometres before falling onto the Raunthi Gadhera stream floor. There was thus a huge mass of rock, ice and other debris that stayed that way for a while. It looks like it stayed that way for three days and the ice and snow started to melt from the heat. It was a clear sky. Eventually, the pressure created by the volume of water and other debris forced its way down the valley and led to the flooding and deluge. This was different from a situation like Kedarnath in 2013. There, multiple cloudbursts in June led to a torrent of snow and water that resulted in a flash flood. (This resulted in widespread destruction in Uttarakhand and the loss of nearly 5,700 lives, along with damaged hydropower tunnels as well as destruction of livestock and property.)
What made the mountain peak break?
This is still to be determined. What is likely is that this is a result of decades of freezing and thawing that would have led to weaknesses and cracks forking in those mountain structures. It was not a sudden event, and this underlines the reasons of why we need to keep monitoring the Himalayas. They are fragile and host to several complex processes that need to be monitored. Global warming contributes to the weakening of the glaciers and we need several organisations and specialists working on these aspects to monitor, make models and thereby make predictive forecasts that can warn of such occurrences in the future.
We need some ground-based measurements and we have already made a scientific plan to be able to access these mountains in the summer. We will have to investigate if there was some tectonic activity, or a blast from somewhere higher up that triggered fault-lines. We don’t know yet and it will take some time to establish that. But imagine a heap of rice. If the base is not strong and grains accumulate, there will at some point be a single rice grain, that when added to the heap, will cause it to crumble. So we have to determine structural weaknesses too.
Do such accidents show that it’s foolhardy to construct hydropower projects in Uttarakhand beyond a certain elevation?
Ideally, before projects are conceived, there are expert assessments done and these are expected to be followed.
Published - February 10, 2021 05:55 pm IST
