A Rare Phenomenon Makes Some Glaciers Extremely Dangerous

If the overwhelming majority of glaciers melt without causing any damage (at least immediately), some of them decline in a completely different way. Under certain conditions, they can detach themselves from their rocky bases to begin a slide that nothing can slow down. This phenomenon, called “ glacial surge », concerns approximately 1% of the world’s glaciers; when it occurs, these colossi can move at astonishing speeds, sometimes 10 to 100 times faster than normal.

Why is it dangerous?

A glacier is a colossal mass of water that can weigh from 50 million to several billion tons; it is held only by the force of friction and gravity which presses it against its base. Normally, meltwater circulates under this mass via a network of tunnels which evacuate it to the outside and the ice thus remains firmly anchored to the rocky ground. The heavier the glacier, the more it crushes the ice against the rock, which exerts a colossal friction force: when it melts, it only advances a few centimeters per day, because it is slowed down by its own base.

In glaciers affected by surge, this network of tunnels is blocked and the meltwater can no longer drain properly. It accumulates under the ice, increases in pressure, lifts the enormous mass of ice by only a few millimeters, and this pressure cancels out the friction: the glacier then detaches from its base and skates on a pressurized film of water.

In some cases, it can happen that a glacier advances 60 meters per day; its walls are crushed by mechanical stress, creating crevices and seracs that wreck the area where it moves.

By progressing beyond its usual bed, the glacial tongue can obstruct the course of a neighboring river and create a completely shaky natural dam. Behind this newly formed wall of ice, millions of m³ of water inflate this improvised reservoir, and when the pressure is too intense or the glacier fractures further, the dam can fail without warning.

When such a flood occurs, the waters, loaded with blocks of ice and debris, pulverize everything in their path. In the Karakoram (northern Pakistan), between 2019 and 2022, the Shisper glacier, in the space of a few months, began a meteoric push forward, hitting the bed of a river head-on flowing from the nearby Muchuhar Glacier valley.

The dam thus formed, several hundred meters thick, completely blocked its flow. In May 2022, under the influence of an early heat wave that accelerated the melting, the water pressure became unbearable for the ice dam. The latter let go brutally, releasing an extremely violent glacial lake drain, which devastated everything in its path.

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This flash flood swept down the Hunza Valley, causing enormous material damage, starting with the Hassanabad Bridge on the Karakoram Highway (see video above). This road is the only land route linking Pakistan to China, a vital artery for trade and supply to these isolated regions. After this surge, entire villages lost their arable land and the region found itself cut off from the rest of the world.

Surges existed long before man appeared on Earthbecause they are intrinsically part of the life cycle of certain glaciers. Nevertheless, they tend to become more difficult to anticipate than before due to global warming in certain regions of the globe (Arctic, Himalayas, Andes, Central Asia, in particular), because rising temperatures and changes in precipitation patterns disrupt the thermal balance of these giants. For the moment, no homogeneous trend is not yet established on a global scalebut these episodes could be the subject closer monitoring in the decades to come. If the phenomenon accelerates, its human and financial cost would, therefore, also risk flying away.