Catastrophic Earthquakes In Nepal During Medieval Era

A team of international researchers found that during the medieval period three catastrophic earthquakes occurred in Nepal. These earthquakes took place during the years 1100, 1255 and 1344 with magnitudes of Mw 8, which resulted in massive collapses, mass movements along with the redistribution of material, and debris flows on mountain ranges.

In their study, the researchers found that flows of rock, sand and gravel debris poured over a distance of 60 km from the high mountain peaks of the Annapurna massif to downstream. Annapurna is a collection of mountains that makes up the Himalayas. Pokhara is Nepal's second largest town, and it was built on massive debris deposits, which are affiliated with strong medieval earthquakes.

"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," Christoff Andermann, coauthor of the study from the GFZ German Research Centre for Geosciences, said in a news release.

A massive boulder that was situated on top of sediment depositions, which weighed about 300 tons with a ten meters diameter, was of great interest to the researchers. On the top of the boulder, the team measured the concentration of a Beryllium isotope, which is generated from cosmogenic radiation. The results revealed that deposition from the boulder matched another massive earthquake that took place in 1681.

The researchers are not sure if the large boulder was transported by the last dated earthquake or if was moved by strong shaking. However, it is possible that the movement of the large boulder was linked to this strong earthquake, according to the researchers.

The researchers' study is shedding new light on the movement of large volumes of materials, which is affiliated with massive earthquakes. In addition, dating of these earthquakes could provide significant information of future recurrences of earthquakes in the Himalayas. It also provides new data on the role of earthquakes and how they shape mountain ranges and landscapes.

The findings of this study were published in Science.

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