Nepal’s second-largest city and its leading tourist hub Pokhara is built on massive debris deposits which are associated with strong medieval earthquakes, a new study has found.
Three quakes, in 1100, 1255 and 1344, with magnitudes of around eight moment magnitude (Mw) triggered large-scale collapses, mass wasting and initiated the redistribution of material by catastrophic debris flows on the mountain range.
An international team of scientists led by the University of Potsdam in Germany has discovered that these flows of gravel, rocks and sand have poured over a distance of more than 60 kilometres from the high mountain peaks of the Annapurna massif downstream.
“We have dated the lake sediments in the dammed tributary valleys using 14C radiocarbon. The measured ages of the sediment depositions coincide with the timing of documented large earthquakes in the region,” said Christoff Andermann from the GFZ German Research Centre for Geosciences in Potsdam. One big boulder, situated on top of the sediment depositions, has raised the interest of the scientists.