The failure is also unique in that

The failure is also unique in that it occurred with no apparent signs of distress prior to failure. High quality video from a drone flown over Dam I only seven days prior to the failure also showed no signs of distress. The dam was extensively monitored using a combination of survey monuments along the crest of the dam, inclinometers to measure internal deformations, ground-based radar to monitor surface deformations of the face of the dam, and piezometers to measure changes in internal water levels, among other instruments. None of these methods detected any significant deformations or changes prior to failure. Post-failure satellite image analyses indicated slow and essentially continuous small downward deformations of less than 36 millimeters per year (mm/year) were occurring on the dam face in the year prior to the failure, with some acceleration of deformation during the wet season. In the lower part of the dam, the deformations measured in the 12 months prior to failure included horizontal deformations ranging from 10 to 30 mm. Such deformations are consistent with slow, long-term settlement of the dam, and would not alone be indicative of a precursor to failure.