For 50 years up to 1966, millions of cubic metres of excavated mining debris from the National Coal Board's Merthyr Vale Colliery were deposited on the side of Mynydd Merthyr, directly above the village of Aberfan. Early on the morning of Friday, 21 October 1966, after several days of heavy rain, a subsidence of about 3–6 metres (10–20 ft) occurred. At 9.15 am more than 150,000 cubic metres (5,300,000 cu ft) of water-saturated debris broke away and flowed down hill at high speed. The front part of the mass became liquefied and moved down the slope as a series of viscous surges. 120,000 cubic metres (4,200,000 cu ft) of debris were deposited on the lower slopes of the mountain, but a mass of over 40,000 cubic metres (1,400,000 cu ft) of debris smashed into the village in a slurry 12 metres (39 ft) deep. The slide destroyed a farm and 20 terraced houses along Moy Road and slammed into the northern side of the Pantglas Junior School and part of the separate senior school, demolishing most of the structures and filling the classrooms with thick mud and rubble up to 10 metres (33 ft) deep. The final death toll was 144. In addition to five of their teachers, 116 of the dead were children between the ages of seven and 10 – almost half of the children at the Pantglas Junior School.