Marcel Hürlimann: The melting of more glaciers in the Himalayas is a danger

BarcelonaThe great flood between Nepal and Tibet has caused hundreds of deaths and more than a thousand missing. We speak with Marcel Hürlimann, professor at the UPC and expert in natural risks, to clarify the nature of this phenomenon.

There has been considerable confusion about the origin of the catastrophe. There was talk of an earthquake, but it has been ruled out. How is this confusion explained?

— It is complex. It has been verified that there was no prior earthquake. What happens is that an avalanche or landslide of these dimensions generates vibrations so strong that seismographs register them as seismic signals. Distinguishing the origin of these signals – whether it is an earthquake, a volcanic eruption, or a large landslide – is difficult, but possible. Thanks to satellite images, we know that the cause was purely the collapse of the mountain and not a seismic event.

Did a glacier fall?

— According to the commission of experts on glaciers and permafrost [soil that remains permanently frozen], it seems that a part of the rocky massif of Langtang Lirung peak, at an altitude of about 5,000 meters, broke off, and on top of the massif there was a very powerful glacier. When the massif detached, it dragged the glacier and caused a gigantic avalanche of ice, rocks, and sediments that descended into the valleys.

How was so much water generated?

— The avalanche descends with so much mechanical energy that it is capable of melting ice very quickly and transforming it into water. As it advances down the valley, this water incorporates sediments from the bottom and its volume multiplies. We are talking about an initial volume of about 100 million cubic meters. To give us an idea, last year in Switzerland there was a similar avalanche incident that covered an entire village, Blatten. Well, this Himalayan episode has been between 10 and 30 times larger than the one in Switzerland. It is an absolutely extreme event.

What is the relationship between the instability of these rocks and climate change?

— It plays a decisive role on glaciers and permafrost. With climate change, temperatures rise, ice melts and water filters into the cracks of the rocky massif. This generates enormous instability in the rock. The massif that broke off on Wednesday was in a zone of "temperate permafrost", where temperature fluctuations of the zero isotherm are constant. In fact, the Himalayas is currently the area of the planet where this ground is thawing most rapidly and where the mountain suffers most movements and instability, which makes the melting of more glaciers a danger.

Therefore, should we expect these types of catastrophic episodes to repeat more often?

— Everything points to yes. Scientifically, it has already been proven that rising temperatures make high mountains much more unstable. I don't have direct data from the Himalayas because I don't work there personally, but all hypotheses and models indicate that, indeed, there will be more extreme episodes in the future.

How can we foresee these landslides and protect the valleys?

— We already have the technology and scientific knowledge. Using satellites, we can daily measure millimeter movements of the ground to detect instabilities before they occur. There are also early warning systems or vibration sensors in the valleys. The real limitation is not technical, but economic: implementing all this costs a lot of money.

Why is access for rescue teams to the affected area proving so difficult?

— On the one hand, the mixture of water and sediment that remains is like liquid concrete, and you have to be very careful where you step. In addition, the roads have been destroyed. On the other hand, there is a real danger that a second episode will occur. Satellite images show that an almost vertical scar has been left on the mountain. That is to say, a part of the glacier behind the one that has broken off remains in an unstable state. You cannot send rescue teams to work near a place where another fragment of the glacier can still fall.