Due to heavy rainfall debris mass got saturated. Presence of weakness plane at the interface of rock and overburden mass facilitatedsliding of overburden on this plane. Also, road cutting at steeper angle during  widening of road  aggravated the problem.
An Interim Report on Preliminary  Geological  Slope Stability Assessment of the Recent Disaster Affected Areas in Parts of Chamoli District, Uttarakhand by Bhupendra Singh, Bhupender Singh, Ajay Kumar and Arindam Roy, Senior Geologists, M-IV, NR GSI Dehr
UK_CHA_NH_ 059
Patalganga –II, left bank of Ganesh Ganga
Toe wall for support to overburden, slope modification by benching, mulching of suitable plants to arrest soil erosion.
Heavy rainfall caused saturation of overburden and reduction in its shear strength. Road cutting at steep angle and presence of shear zone at the interface of rock and overburden provided the sliding plane.