So he visited the site the following year, becoming only the second geologist known to have done so, and took some samples.
Examining the surrounding cliffs for signs of a collapse, he noticed that a peak known as Annapurna IV offered a relatively smooth, steep face which seemed to fit.
Back home, he sent samples from the rubble field, the rock core and others from the path the landslide might have taken for dating.
Should their ages roughly correspond, that would suggest they were linked to the same event.
By measuring the abundance of chlorine-36 (a radioactive isotope which accumulates in surface rocks and decays once they are buried), and carbon-14 (another which accumulates in living matter and decays after death), his colleagues dated the samples to the late 12th century, and to within a couple of decades of each other.
That is within the accuracy limits of the dating techniques themselves.
Besides shedding light on a previously unknown cataclysm, Dr Lave’s work could plug a gap in the dominant explanation for why mountains stop growing, which is known as the “glacial buzzsaw” hypothesis.
Under this model, it is glaciers, which are extremely effective at carving scoops out of mountains, that are mostly responsible for curbing their growth.
The problem with that theory, says Dr Rowan, is that there are some peaks that manage to escape the erosive effect of glaciers, and then grow so steeply that glaciers can no longer stick to their sides.
“The question is,” she asks, “what stops these mountains getting bigger?”
Landslides could well be one answer.
While the exact trigger for the Annapurna landslide is unknown, Dr Lave’s idea is that, with nothing to shave rock off their tips, very high mountains simply keep growing until their weight is too much for their lower slopes—which do still experience erosion—to support.
Working out exactly how and when the tipping point is reached will require examining other such rockslides.
Unfortunately, due to the actions of both glaciers and swollen rivers during the monsoon season, the rubble from the Annapurna landslip is vanishing fast.
Dr Lave reckons that only about 10% of the dislodged material now remains in place.
Older rockslides, assuming there were any, may already be impossible to reconstruct.