Believe me when I say there is no missing the Frank Slide as you drive along Highway #3 through the Crowsnest Pass in southern Alberta, near the British Columbia border.
I’m a sucker for geologically related stories. Past articles I’ve posted include the formation of the Baja Peninsula, the fossils of the Burgess Shale, time travelling through the Canadian Badlands, the journey of Big Rock erratic, and the origin of Victoria Falls. So now – the fast, furious and unforgiving Frank Slide.
From either direction you see the evidence of a massive rockslide well before reaching the area. A large bare section of the mountain is easily visible as you drive westward. Then soon the landscape changes from green hills and trees to rocks and boulders – including some very enormous ones!
The unimaginable happens
On April 29, 1903 at 4:10 AM, the quiet coal mining town of Frank, Alberta, Canada, population 600, is abruptly awoken by sound and rumbling later reported heard 200 kilometres (125 miles) away.
A section of Turtle Mountain some 1000 metres (3300 feet) wide, 425 metres (1390 feet) high and 150 metres (490 feet) thick, breaks free and careens towards the town of Frank.
In less than 100 seconds, the rock debris rockets down the mountain, across the valley floor, and partially up the hills on the opposite side, annihilating the Frank Mine buildings, the railway camp and the east side of Frank on its way. The video below illustrates this.
The rockslide reaches speeds up to 110 kilometres/hour (70 miles per hour). In total the Frank Slide debris covers 300 hectares (750 acres) with an average thickness of 14 metres (47 feet).
Try to imagine it. The sound, the wind, the ground shaking. All in one and a half minutes. Fast, furious and unforgiving!
No one has a chance to react as most are still in bed. It is dark out so the people of Frank cannot see what is coming. About 100 to 120 individuals are in the path of the rockslide. Of these, an estimated 70 to 90 people lose their lives. We will never know the exact number of casualties as only 12 bodies are recovered shortly after the catastrophic event.
20 miners are working at the Frank coal mine at the time of the rockslide. Three unlucky souls are taking a well deserved break on surface and don’t stand a chance. The remaining 17 miners are trapped in the mine, but alive. After unsuccessfully trying to dig their way back out through the entrance, one of the miners has an idea. They dig through a coal seam that reaches the surface.
After several grueling hours they breath in fresh air, but emerging is too dangerous due to rock fall. They divert there digging to a safer spot on surface. All 17 survive.
The rockslide obliterates the railroad camp, killing all 12 rail workers residing there. Miraculously, 128 other rail workers avoid the same fate. Their scheduled train ride from a small town 90 kilometres (55 miles) for the previous day did not materialize.
One brave Canadian Pacific Railway brakeman rushes across the very unstable field of rocks, to warn an oncoming train about the rockslide. He is successful, and most likely prevents even more casualties.
What caused the Frank Slide?
In a foreshadowing way, stories passed down by the Blackfoot and Ktunaxa First Nations refer to Turtle Mountain as “the mountain that moves.”
The Geologic Survey of Canada (GSC) concludes the primary cause of the slide was a precarious anticline formation. In simple terms, older limestone rested on top of younger, softer rock resulting in an unstable, steep cliff.
Cracks in Turtle Mountain allowed water to penetrate the critical stress areas within. A warm and wet winter created repeated thawing and freezing within the cracks of the mountain. On the night of the Frank Slide, a sudden dip in temperature to -18 C (-0.4 F) may have contributed to the breaking point.
A more controversial possible contributing factor, is the active coal mining under Turtle Mountain at the time of the Frank Slide. Later studies theorize the mountain was in a state of unforgiving equilibrium. This means the coal mining activity may have been enough to upset the equilibrium and allow the other destabilizing factors to take hold.
Why was the Frank Slide so Fast, Furious and Unforgiving?
Two theories have been debated as to how the rockslide was able to move so rapidly and reach so far.
The “air cushion” theory suggests that a layer of air became trapped between the rockslide debris and the mountain. This allowed the rock to travel faster and farther over a cushion of air.
The “acoustic fluidization” concept theorizes the large mass of moving material generated seismic energy that reduced friction between the debris and the mountain, again allowing faster and farther travel.
Either way, the Frank Slide acted very much like a typical large snow avalanche, so the new term of “debris avalanche’ was created.
Whatever the cause, I think one could use “fast, furious and unforgiving” to describe the Frank Slide.