REPEAT STRUCTURE-FROM-MOTION SURVEYING OF A HAZARDOUS MASS WASTING FEATURE IN STEEP TERRAIN NEAR DURANGO, CO
To better understand how the mass wasting feature changes over time and what hazard it may present in the future, a repeat-surveying campaign utilizing a cheap, consumer-grade UAV paired with RTK GPS and structure-from-motion processing was launched in Oct 2016. Five surveys have been conducted in total, each taking place in April (post-snowmelt) or October (post-monsoon).
Although challenging to conduct on the steep slopes of the study area, the surveys yielded digital terrain models with spatial resolution as high as 3 cm/pixel and remarkably precise georeferencing. Comparison of successive surveys in GIS reveals a zone of progressive scarp failure near the main rockfall mass, and multiple zones of material accumulation downslope. Nearly all movement occurred during spring snowmelt, while the monsoon exerted a surprisingly minimal effect. During the study period, a newly-formed, boulder-dammed debris field was identified as a future hazard; that dam broke in 2019, sending the largest, coarsest debris flow yet downslope and burying the roadway at the base of the slope in up to 5 m of debris.
These results support the utility of using UAVs paired with structure-from-motion to monitor rapidly-changing geohazards, despite the extreme terrain and ever-evolving survey strategies.