Basin 3 at a coal mine broke and released 500,000 m³ of coal sludge (water, dust, clay, lower-grade coal and impurities), which swept away Basins 2 and 1. A 10-m high wave was unleashed, engulfing 16 small towns. 125 of the 5,000 residents affected were killed, another 1,120 were injured and 4,000 left homeless. A total of 507 houses, 44 mobile homes and 30 businesses were destroyed.

Precipitation had fallen for several days leading up to the accident and caused the rise in water level inside the basins, prompting the site operator to proceed with periodic level recordings every 2 hours, yet without issuing the order to evacuate the downstream population. At 8 am on 26 February, a technician noted that the water level had reached the crest on dam no. 3. Five minutes later, this dam enclosure, which had become saturated with water, failed.

Basin 3 had been built on foundations of coal sludge instead of a soil with the requisite geotechnical characteristics. In 1967, the Department of the Interior had indicated to West Virginia authorities the instability and hazard associated with 30 dams located in this State, including this one (Buffalo Creek). This earlier study had been conducted after the 1966 Aberfan accident in the U.K., resulting in 147 deaths. The Buffalo Creek Basin, built prior to passage of the federal “Coal Mine Health and Safety Act”, would not have been approved for construction once this act had been promulgated.

In June 1978, the operator paid $18.3 million to survivors and another $1 million to the State of West Virginia following the outcome of an arbitration proceeding (out-of-court settlement between the parties).