In geology, unlike business, nothing is too big to fail.
Mountains offer the most spectacular example.
Pushed up by the crumpling of Earth’s crust following the collision of tectonic plates, they could in theory keep rising almost indefinitely.
In practice, they do not.
A suite of geological processes—including the grinding of glaciers, the gentle impact of rain, and forcible cracking by freezing and thawing of water—erode them down to size.
In a paper published in Nature Jerome Lave, a geologist at the University of Lorraine, describes another, much more spectacular mechanism.
Dr Lave has collected evidence suggesting that, in around 1190, an enormous landslide slashed perhaps 500 metres from the height of Annapurna IV, a mountain in the Himalayas that stands about 7,500 metres high today.
If he is right, it would be one of the biggest landslips ever recorded.
The falling mountain top would have displaced up to 27 cubic kilometres of rock—roughly enough to bury the entirety of Manhattan to about the height of the Empire State Building.
As the rubble crashed down, the energy released would have been equivalent to around six times that of the Tsar Bomba, the biggest nuclear weapon ever detonated.
“I don’t think I could imagine what it would sound like,” says Ann Rowan, a geologist at the University of Bergen who was not involved in Dr Lave’s work.
Dr Lave’s suspicions were aroused while doing fieldwork in the Ganga plain in Nepal in 2012.
He noticed that the ground beneath his feet had an unusual composition.
A 50-metre core drilled out of the rock showed an average concentration of limestone of around 10%.
But for one 4-metre stretch the concentration rose to nearly 50%, “which is enormous, and completely abnormal”, he says.
This suggested that the rocks in question had made their way to the Ganga plain from the Annapurna massif, hundreds of kilometres away.
That, in turn, hinted at a massive landslide in the (geologically) recent past.
After examining satellite images of the massif, and taking a helicopter ride to have a look for himself, Dr Lave spotted a large rubble field which looked like it could have been caused by the same event.