This dam failure is unique in that

This dam failure is unique in that there are high quality video images of the event that provide insight into the failure mechanism. The videos clearly show a slope failure within the dam starting from the crest and extending to an area just above the First Raising (the Starter Dam). The dam crest dropped and the area above the toe region bulged outwards before the surface of the dam broke apart. The failure extended across much of the face of the dam and collapse of the slope was complete in less than 10 seconds, with 9.7 million cubic meters (Mm3) of material (representing approximately 75 percent (%) of the stored tailings) flowing out of the dam in less than 5 minutes (min). The material in the dam showed a sudden and significant loss of strength and rapidly became a heavy liquid that flowed downstream at a high speed. The videos show that the initial failure was relatively shallow and was followed by a series of rapid shallow slips with steep back slopes that progressed backwards into the tailings impoundment. Based on these observations, it is clear that the failure was the result of flow (static) liquefaction within the materials of the dam. The significant and sudden strength loss indicates that the materials within the dam were brittle.