During the first three weeks of October 1966 there were of rainfall, nearly half of which were in the third week. During the night of 20–21 October the peak of Tip 7 subsided by and the rails on which the spoil was transported to the top of the tip fell into the resulting hole. The spoil movement was discovered at 7:30am by the first members of the morning shift manning the heaps. One of the workers walked to the colliery to report the slip; he returned with the supervisor for the tips, and it was decided that no further work would be done that day, but that a new tipping position would be decided on the following week.