A catastrophic debris flow in the Rishiganga and Dhauli ganga river in Uttarakhand, India on 7th February 2021 left a trail of disaster. Around 200 people lost their lives, two hydro-power project were badly damaged and a bridge across the Rishiganga River was washed off in the event. Study shows that the debris flow is caused due detachment of 0.59 km2 right lobe of a hanging glacier and resultant ice-rock avalanche. This right lobe of the glacier was located over a mountain slope having an average slope of 35o at 4700–5555 m a.s.l. and travelled 12.4 km before hitting the infrastructure projects. Role of precipitation, snow cover, land surface temperature and permafrost processes were investigated for identifying causes of the event. Since 2012, monsoon precipitation and mean annual land surface temperature (LST) showed significant increasing trend. Snow cover during monsoon months showed increasing trend and September, October and November experienced decreasing trend at glacier elevations. Mean annual LST increased from − 0.3 oC in 2012 to a peak of 0.4 oC in 2016. Central lobe of the glacier advanced during this period and eventually fell off in 2016 suggesting that the LST warming forced reduction of frictional drag at the interface facilitating it advancement and eventual dislodgement. Permafrost modelling suggest warm permafrost below 50 m and conditions favorable for intense frost cracking at to 10–15 m. At ~ 40 m depth, the delayed response of 2012–2016 warming produced peak positive temperature conditions by December and probably facilitated the formation of thin film of water at the deeper layers acting as a lubricant for glacier sliding. It is also suggested that the increase in summer precipitation might have forced thickening of the accumulation area and thereby increasing the shear stress for sliding of the glacier. It is proposed that the recent change in the weather conditions in the region is primarily responsible for this event through geological, glaciological and permafrost processes. Flood modeling study suggest a flood volume of ~ 10 MCM generating 24.5 m flow depth at the bridge site with 12.7 m/s flow velocity. The event highlighted the need for improved monitoring of the cryospheric areas of the Himalaya to capture the early warning signs for better preparedness.