The enormous devastation in Nepal and Tibet appears to be the result of a ticking time bomb that went unnoticed until it was too late. That is the initial assessment experts make barely a day later about the broken glacier in the Himalayas. Although more clarity is expected in the coming days and weeks about what has transpired, it is possible that this time bomb was partly triggered by global warming.
"On new satellite images from this morning, you can very clearly see that a part of a glacier has broken off. It measures about 1.5 by 1 kilometer," says professor of mountain hydrology Walter Immerzeel from Utrecht University. "I don't know exactly how thick, but think of 100 or 200 meters. That mass came down through a steep valley and then ended up in the border river between Tibet and Nepal."
There are still questions about the further circumstances. "Residents have indicated that the river flow decreased somewhat for a while first," says earth scientist Tjalling de Haas from Utrecht University. "That could indicate that the river was blocked by a landslide. Then a kind of dam forms, behind which river water begins to accumulate." That becomes a temporary lake.
More frequent natural disasters
But that natural dam can break, for example due to the ever-increasing pressure from the growing amount of water, or because a large mass suddenly falls into it. "How exactly that happened now is not clear. For example, more could have broken off that ended up in that accumulated river water." However, there are also other scenarios. In any case: a gigantic flood surge has arisen.
Immerzeel certainly knows the Langtang valley well. He has visited the region about twenty times since 2012 and conducted research for years in a side valley a few kilometers from the border post where the devastating flood passed yesterday. It is an area familiar with natural disasters: in 2015 there was a severe earthquake that caused thousands of deaths. People also died in his research valley.
The images of the border post between Nepal and Tibet went around the world yesterday:
Yet Immerzeel also did not expect a disaster of this magnitude at this specific location. "You really cannot predict or foresee these kinds of super-extreme events." His fellow scientist De Haas thinks the same. "Those mountain areas are very large and there are rock walls everywhere that can collapse. Exactly where is difficult to predict."
Minutes matter
Even if you notice it, it is a matter of minutes, says flood risk researcher Tim Busker from the Free University in Amsterdam. "Between the glacier breaking off and the moment the flood wave reached the border crossing was seven minutes. That is too little. People would have to act very quickly. I have read that lives were saved with warnings from the flood service, but that was more downstream."
Whether the danger is definitively over after yesterday's disaster is not yet clear. In theory, at another point, due to all the shifts, a large accumulation of water can form again, and the same process can repeat itself, although the scale is probably smaller than yesterday. China and Nepal warn that a new dam lake has now formed, which could possibly lead to a new flood.
More warming, more unstable mountains
This problem may occur more often in a changing climate. Professor Immerzeel: "It is now of course an enormous coincidence of circumstances that makes it such a big disaster." It is a very narrow valley, the buildings are close along the river, and the rainy season coincides with the melting season.
But even without all those factors that make it a big disaster, the process underlying this will occur more often on a warming planet. "I think that chance is high due to warming. The permafrost high in the mountains holds the rocks together. That is melting further and further. And then you have the meltwater: if that gets between the glacier and the rocks, the whole thing can start sliding."
Further global warming in mountain areas worldwide equals further thawing and melting. Even if further warming stops, glaciers will continue to melt for centuries, scientists concluded just last year. This means the problem will occur more often, on equally large or smaller scales.
A day after the deadly flood that flowed through Nepal, the impact becomes visible. In this story, they show what natural force struck the area: