The hill slope was cut for road widening and remained unsupported. During heavy rainfall the overburden material  resting over steep slope got saturated, lost its shear strength and started flowing down. It had retrogressive impact on the slope. 

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_ 029
Upstream of Alkhanda – Birhi Confluence
Slope dressing with benches, improvement of drainage networks, breast wall with weep holes and lined toe drain.
Saturation of overburden mass due to heavy rainfall resulted in mobilization of debris material along the slope, planar failure in rock.