At around 7:30am on the 21st of October 1966 workers arriving at the site of a coal mine near the village of Aberfan in Wales discovered that one of several spoil heaps on site had shifted during the night. Supervisors called a halt to any work that day, and began to assess the damage. They were still doing so at 9:15am, when a huge amount of material broke away from the heap and flowed downhill in a giant wave, directly towards the village below.