Immense India Flash Flood Might Have Been Part Of Worrying Climate Change Hazard

Rescue workers in India after last weekend's huge flash
flood, initially blamed on a glacial lake failure. 

An extreme flash flood swept through part of the Indian state of Uttarakhand over last weekend, killing as many as 125 people and causing a swath of destruction through a mountain valley. 

According to the BBC, a wall of water and rocks poured down the valley, bursting through a dam and sweeping away pretty much everything in its path. 

News reports, at least the ones I've seen so far, don't make it clear why such a huge flood hit that part of India. However, initial speculation pointed toward something called a glacial lake outburst flood, and it's one more in a long list of dangerous effects that could easily be brought on by climate change. 

It turns out the disaster might have had another source: A huge chunk of snow fell off a mountain near Raini village, perhaps temporarily blocking a river, according to the Indian Express. 

Very heavy snow fell in the mountains on February 5 and 6, then began melting on February 7. The melting probably caused the snow to slide off the sides of the mountain, picking up water and soil along the way.

This mess, again, possibly briefly collecting behind a brief debris dam, then roared down the valley. The avalanche could have released 3 to 4 cubic meters of water into the rivers affected by the flash flood, says the Indian Express. 

If these scientists and observers are correct, this wasn't a glacial lake outburst.  However the phenomenon is still a huge threat that could cause as big or worse disasters. 

Climate change is making mountain glaciers retreat in most of the world, including the Himalayas. As the glaciers melt, the resulting water sometimes collects in a lake a little below the retreating glacier.  These lakes and potential floods also occur in the European Alps, Central Asia, South America, Iceland and other places. 

The material holding back the water is often weak and unstable.  The dam might consist of a pile of rocks and soil left behind a moving glacier. Or the dam might be a melting wall of ice that finally gives way. 

The water will finally break through the dam, maybe because of heavy rain or the splash from a chunk of ice falling off the glacier.  The hole in the dam keeps widening, so soon a torrent of water roars down a valley toward places where people are.  The wall of water picks up rocks and other material from the destroyed dam or other areas downstream, so the flash flood is full of battering rams that destroy everything in their path. 

These can happen repeatedly in the same area.  The dam that was breached by the glacial lake can re-form, then collapse again.  

There has not been an apparent, real increase in these floods due to climate change, but scientists do worry this will become an increasing problem in areas with mountain glaciers as the world continues to warm. 

Ominously, glacial lakes are growing and becoming more numerous in the Himalayas as glaciers melt, so you can see how this is going to be issue to be reckoned with in future generations.