Q1.
A devastating flood struck the Chamoli district in Uttarakhand in February 2021 in which many people and livestock lost their lives. There was severe damage to buildings, roads, bridges, and hydel projects, and connectivity to villages was adversely affected. Can you find out the reasons that led to the sudden and unexpected flood?
Answer
The flood came from the mountain itself, not from rain. That is the key to the whole event — it happened in February, in the middle of winter, when there is no monsoon and no snowmelt to speak of. So the water had to be released suddenly from something already stored high up.
The chain of reasons:
- A mass of rock and ice broke away high on a steep slope. The Chamoli area lies in the high Himalaya, where slopes are very steep, the rock is fractured, and repeated freezing and thawing prises it apart — the physical weathering described on page 19.
- The falling mass shattered on impact and mixed with ice and snow. The heat of the fall melted part of the ice, turning solid debris into a fast-moving slurry of water, mud and boulders.
- The slurry poured into a narrow valley. A steep, narrow Himalayan valley cannot spread a flood out sideways, so the water rose into a wall instead of a sheet, and travelled downstream at great speed.
- It reached the Rishiganga and Dhauliganga rivers, and struck what lay in the valley floor — bridges, roads and two hydel project sites, where workers were inside tunnels. This is why the loss of life was concentrated and sudden.
Why it was "sudden and unexpected":
- There was no rainfall warning to go by, because rain was not the trigger. Flood warning systems watch the weather, and the weather that day was ordinary.
- The source was high, remote and unmonitored — nobody was watching that slope.
- The flood travelled down a steep gradient, so the time between the collapse and its arrival in the villages was minutes, not hours.
The deeper reason — why the Himalaya is fragile at all: it is a young fold mountain, still being pushed up by the collision of the Indo-Australian and Eurasian plates (page 15). Young mountains are high, steep and made of rock that has been crushed and fractured by that same collision. Add glaciers and daily freeze–thaw, and the slopes are loaded with loose material waiting to move. Building roads, tunnels and hydel projects at the bottom of such valleys puts people directly in the path of whatever comes down.
Connect it forward: pages 33–35 name the three hazards that combine in an event like this — a landslide or rock-and-ice avalanche starting it, and a GLOF as the closely related danger, since rising temperatures are enlarging glacial lakes across the Himalaya and weakening the ice and moraine dams that hold them.
Try this: find newspaper reports of the Chamoli event and note down the times — when the collapse happened and when the water reached each village. That time gap is exactly what an early-warning system has to work inside.