A colliery spoil tip slips onto houses and a school in the village of Aberfan in Wales, killing 144 people, 116 of whom were schoolchildren.

The Aberfan disaster was the catastrophic collapse of a colliery spoil tip on 21 October 1966. The tip had been created on a mountain slope above the Welsh village of Aberfan, near Merthyr Tydfil, and overlaid a natural spring. Heavy rain led to a build-up of water within the tip which caused it to suddenly slide downhill as a slurry, killing 116 children and 28 adults as it engulfed Pantglas Junior School and a row of houses. The tip was the responsibility of the National Coal Board (NCB), and the subsequent inquiry placed the blame for the disaster on the organisation and nine named employees.

October 21 is the 294th day of the year in the Gregorian calendar; 71 days remain until the end of the year.