Frank Slide

On April 29, 1903 at 4:10 a.m., 30 million cubic metres of limestone hurtled down the east face of Turtle Mountain. Boulders piled up to 30 metres deep to cover more than 2.5 square kilometres of the Crowsnest River valley in awesome testimony to the destructive power of the Frank Slide. In only 100 seconds, boulders were spread across the 1000 metre wide valley and 120 metres up the opposite valley wall. Part of the town of Frank was buried, the rail line barricaded, the entrance to the coal mine was temporarily sealed, and over 70 people were killed. Because of the potential for further slope failure, Turtle Mountain is monitored for any movement. The Frank Slide Interpretive Centre sits high above the rubble across the valley from the mountain, and a 1.5-kilometre trail leads down to the slide itself.

This rockslide has become the classic example of mass movement because it is one of the largest slides to have eyewitness descriptions as well as numerous detailed geological reports.

Many miners believe that mining and blasting at the base of the mountain weakened the mountain. Before the slide, they had commented on the cracking of the wood supports in the mine. As well, prior to the slide, cracks had formed in the exposed bedrock at the mountain's summit. Local weather conditions just before the slide indicates that it was hot, so snow would have melted and filled the cracks with water. The temperature turned cold on the night of April 28 and the water likely froze and expanded, wedging the cracks apart. This, then, may have been the final strain on an already unbalanced mountain.

Whatever the reason, once the rock mass was in motion, it slid down along bedding planes in the limestone and then followed the plane of the fault at the foot of the mountain.