Recent cloudburst-induced landslides around Okhimath, Uttarakhand

摘要

On 13 September 2012, the Okhimath region in Rudraprayag district, Uttarakhand was revisited by cloudburstinduced landslides which killed 66 people and damaged land and property (Figure 1). On that day, Okhimath Tehshil received 212.5 mm of rainfall. Cloudburst by definition is a localized torrential rain event in which the downpour rate is 200–1000 mm/h (fall down with around 10 m/sec), with drop size between 4 and 6 mm (ref. 1). Such a highfocused rain event results in the increase in pore water pressure. If such highintensity rain falls on the unconsolidated debris-laden moderate to steep slopes (as was the case around Okhimath), it causes decrease in the frictional drag with a concomitant increase in the shear stress 2 . The final outcome is the generation of multiple landslides of varying magnitude that will be governed by the debris thickness and the underlying lithology.