Integration of ground-based radar and satellite InSAR data for the analysis of an unexpected slope failure in an open-pit mine

On 17 November 2016, an unexpected slope failure occurred in an undisclosed copper open-pit mine. The nature of the event urged for a thorough back-analysis of slope monitoring data in order to assess its size and temporal evolution, and to determine whether precursors potentially able to anticipate the failure were present. To this aim, satellite InSAR data spanning over the final 9 months before the event were, in retrospect, acquired and coupled with measurements from a ground-based radar that was in use at the time of the failure. Although progressive deformation was detected by the ground-based radar in correspondence of the two uppermost benches in the pit, the satellite InSAR data revealed that the vast majority of the instability actually involved a large part of natural slope above the mine crest. This sector was not visible by the ground-based radar. Thanks to the short revisit time of the Sentinel-1 mission, clear slope accelerating creep was observed for the first time in satellite InSAR measurements over an open-pit mine. The delimitation of the area featuring accelerating creep behavior matched remarkably the source area of the failure as mapped in the field after the event. Considerations on the volume of the instability and on the development of the failure process (both in space and time) were consequently derived. The results provided a clear example of the value of jointly using ground-based and satellite interferometry to reduce the uncertainties inherent to the identification and characterization of impending catastrophic slope failures.