Nepal flood surged at 163kmph, seismic waves detected 19k-km away: Study

The massive ice-rock collapse that triggered Nepal's devastating Aug 26 Bhote Koshi-Trishuli flood sent a torrent surging at speeds up to 163kmph — faster than Pakistani pacer Shoaib Akhtar's world-record delivery of 161.3kmph against England in the 2003 Cricket World Cup. The collapse also generated seismic waves detected as far as 19,000km -- almost half the globe -- away, while more than 60 smaller seismic events were recorded in the preceding two weeks, including a magnitude 2.5 tremor just 17 minutes before the disaster, the first peer-reviewed seismic study of the catastrophe found.Published in scientific journal Seismica, the research was led by Nepalese seismologists Lok Bijaya Adhikari and Shiba Subedi, along with 17 other scientists from seven countries. It found that seismic monitoring could help detect catastrophic mountain collapses and provide crucial warning time to communities downstream, although researchers could not establish whether the earlier tremors were precursors to the disaster.Scientists analysed seismic recordings from 45 monitoring stations in Nepal and Tibet, selecting 19 with high-quality data, alongside satellite imagery and hydrological observations to reconstruct the sequence of events. They traced the collapse to the northern slope of Tsangbu Ri, a 6,781m-high mountain near Langtang Lirung, where an estimated 100 million cubic metres of material, predominantly rock mixed with ice, broke away and unleashed a flood that travelled more than 200km through the Lhende Khola and Trishuli river valleys.The torrent reached a peak speed of around 163kmph along the initial 25km, where the terrain dropped nearly 3,000m, before slowing to approximately 33kmph farther downstream. The collapse generated seismic surface waves travelling at around 4km per second, allowing monitoring stations thousands of kilometres away to detect the event.Researchers also identified more than 60 smaller seismic events in the fortnight before the collapse, including a magnitude 2.5 tremor just 17 minutes and four seconds earlier, less than 10km from its source. Scientists suggested some of these events might have been slide-quakes associated with unstable rock or ice, but they could not establish a causal connection with the disaster.The analysis revealed a second, smaller landslide nearly three hours after the main collapse, involving an estimated 10 million cubic metres of material. Satellite images showed no glacial lake at the source, distinguishing the catastrophe from a conventional glacial lake outburst flood.Researchers said automated systems could potentially identify major collapses and track the resulting flood activity, allowing authorities to issue alerts before floodwaters reached downstream settlements. Such monitoring could complement existing early-warning systems in Himalayan valleys vulnerable to sudden landslides and floods.The Aug 26 disaster killed at least 1,498 people — 1,455 in Nepal and 43 in Tibet — while 5,804 remained missing, including 5,285 in Nepal and 519 across the border, based on separately reported figures.You use AI every day. Now get your AI Quotient. Take the AIQ test.