It was so loud it is said that some people in the town of Cochrane, outside Calgary – over 200 kilometres (120 miles) away – heard the noise from the Frank Slide.Įar-witnesses in and around Frank said the slide lasted approximately 100 seconds and the sound was like steam escaping under high pressure.īased on how far the rocks extend across the Crowsnest River valley and the time the slide lasted, scientists estimate that rocks were moving at speeds up to 120 kilometres/hour (70 miles/hour). People for many kilometres around heard the roar of the slide. How long did it last? How loud was it? How fast were the rocks moving? In the years following the slide, coal mining has been identified by scientists as a secondary or contributing factor, but it was the unstable geological structure that was the main cause of the massive rock avalanche. Immediately following the slide, coal mining, which had begun in 1900, was blamed for the disaster. Turtle Mountain was a mountain ready to fall. Water continued to eat away at the limestone and the freezing and thawing action of water and ice worked to widen the cracks, creating even more instability. Large surface cracks along the summit of the mountain allowed water to enter deep within Turtle Mountain. The erosion by water and ice of sandstone and shale layers on the lower half of the mountain beneath the older layers of limestone on the upper half of the mountain created a significant overhang.
The thrust fault further divides and weakens the layers of rock within the mountain. A major thrust fault – the Turtle Mountain Thrust Fault – runs through the mountain.
The mountain’s once horizontal layers of sedimentary rock had been folded during the mountain building process until almost vertical – the ultimate in mountain instability. The primary cause of the Frank Slide was the unstable geological structure of Turtle Mountain. The Frank Slide occurred at 4:10 in the morning on April 29, 1903. Learn more about Frank Slide: when it occurred, its impact, and if we're likely to see another rock avalanche from Turtle Mountain.