It took nearly 100 years for a Paleozoic boulder-which fell from the Rocky Mountains as part of the historic 1903 Frank Slide-to reach eastern Canada and the end of its 2500 kilometer cross-country odyssey. In a nutshell, that's the story, and that's how the University of Waterloo campus came to be the end-of-the-road for what may be the world's most traveled, rock-from-a-rockslide rock. The Frank Slide boulder currently rests in the Peter Russell Rock Garden.
The Frank slide
The university's well-traveled boulder began its eastern exodus at 4:10 a.m. on April 29th, 1903. At that time it was part of an 82 million tonne mass of rock which fell from the summit of Turtle Mountain onto the coal mining town of Frank. Within 90 seconds, at least 70 people were dead-most still in their beds. Buildings were on fire and survivors cried for help. Even then, the pre-dawn darkness hid the magnitude of the event from most of the people of the Crowsnest Pass-then a clustered grouping of coal mining communities in the Northwest Territories, today part of the Municipality of Crowsnest Pass in southwestern Alberta.
The rockslide buried part of the town. It also obliterated a two kilometer stretch of the Canadian Pacific Railroad, surface buildings of the Canadian American Coal and Coke Company, two ranches, a portion of the Frank-Grassy Mountain Railway line to the historic coal mining town of Lille, a construction camp, and livery stables. Fortunately, most of the town's populace-600 people-lived a stone's throw beyond the area buried. Approximately 100 people were in the direct path of the slide, and 23 of those-mostly children-escaped death.
Early warning
It was a local rancher who gave Turtle Mountain its name-derived from what was envisioned as the outline of an advancing turtle's face and overriding shell. Prior to this contemporary naming of the mountain, it had been reported that the Blackfoot and Kutenai had oral traditions which referred to the mountain as "the mountain that moves." Supporting these statements, it is said that they did not camp in the area which was subsequently impacted by the slide. Certainly the prehistoric people who mined high altitude chert across the valley as much a 5000 years ago and left pictographs near timberline on adjacent Bluff Mountain, had traversed Turtle Mountain's crest and seen the expansive network of summit fissures.
Causes of the slide
The primary cause of the Frank Slide was the mountain's unstable structure. During the later stages of the Rocky Mountain Orogeny, which ended some 70 million years ago, Turtle Mountain was formed as beds of Paleozoic carbonates from the Rundle Group (300-350Ma) were "thrust" to the northeast along the Turtle Mountain Thrust Fault. These deposits overrode structurally weaker-nearly vertical-Mesozoic deposits (sandstones, siltstones, shales, conglomerates, and coal).
The orogeny also deformed the beds of Paleozoic carbonates-folding these sedimentary deposits to form the Turtle Mountain Anticline and creating zones of flexural slip (movement along sedimentary layers caused by the sliding and/or bending of these once-horizontal beds). This upside-down "U" subsequently fractured along its mountain-top fold-action which, increasingly, created a conduit for water to access the mountain's core. Water within the mountain reduced cohesion-particularly between sedimentary layers and deformation fractures-and dissolved the limestone in a cold water solution.
(ABOVE) Cross section of the Frank Slide used with permission of D.M. Cruden and C.B. Beaty.
The Crowsnest Pass is home to some of Canada's most spectacular limestone caves. While it's the elevated expanses of karst passages such as those of Yorkshire Pot (14.5 kilometers of passageways) and Gargantua (6 kilometers) which were created during past millennia-when groundwater was at a much higher elevation-that attract the greatest attention from spelunkers, the Crowsnest valley is still home to several large springs which continue to erode and dissolve the limestone caves through which they flow. Turtle Mountain has a small-dissolved limestone-cave near its South Peak summit and a sulphur spring which continues to "eat" its foundation beneath North Peak. The 9.1° Celsius spring flows at a rate of 450 liters/min.
By the time the orogeny had concluded, Turtle's summit and eastern face were cracked. Beneath these surface fissures-beneath almost the entire mountain-was the Turtle Mountain Thrust Fault. A splay (a divergent "small" fault) also existed. Significantly, water which then entered the gaping summit fractures was draining into the mountain's fractured core.
From bad to worse
Then came the Ice Age. The Pleistocene played a key role in shaping Turtle Mountain for an ensuing rockslide. During periods of glaciation, valley glaciers carved through the Rockies, separating Turtle from Bluff Mountain, its Siamese sister to the north. (Interestingly, Bluff, too, produced a rockslide-much older and of greater volume than the Frank Slide. Bluff's prehistoric rockslide carried its mass into the Gold Creek valley a mere four kilometers from-and within view of-the Frank Slide.)
The glacier which occupied the Crowsnest River valley during the peak of glaciation carved off much of Turtle Mountain's eastern face, action which removed vast quantities of the steeply dipping bedding planes-the mountain's Paleozoic "shell"-and exposed its softer Mesozoic foundation. The subsequent demise of valley ice exposed the ravaged eastern ramparts of the Turtle Mountain Anticline. Worse, it left them without adequate support. In a structural sense, the mountain's eastern face was "left hanging."
Similar conditions existed elsewhere in the Rocky Mountains, and the Frank Slide is but one of an estimated 1000 rockslides to have occurred during the past-post-glacial-10,000 years. Unlike the cascades of rock which fell elsewhere, however, the Frank Slide came-to-town and crashed head-on into Canada's celebrated western exodus.
While Turtle's fickle foundation and its more recent glaciation had set the stage for structural failure, the mountain's eastern face was targeted to receive yet another strategic attack: mining. Glaciation had exposed seams of high quality coal within Turtle Mountain's Mesozoic basement, and entrepreneurs were quick to mine it, doubly quick when it was but a stone's throw from the recently completed (1898) railway. Most of the underground coal was removed by room-and-pillar mining-an excavation strategy which honeycombed the linear-nearly perpendicular-coal seam-a seam which ran parallel to and 1000 meters beneath the mountain's unstable eastern crest.
Between 1900 and April of 1903, more than a quarter of a million tonnes of coal were removed from the mine. Were the mountain a gun, it could be said that it was loaded, aimed, and cocked. What pulled the trigger?
Mining played with the trigger, but may not have pulled it. Men working underground had reported strange movements as much as seven months prior to that fateful morning of 1903. Large timbers had cracked, and coal-under pressure-had "mined itself" at night. Early mornings were particularly active. There were times when the mine pitched as if rocked by an ocean wave! Yet, during the rockslide, the mine's internal workings suffered little damage; some tunnels pinched closed, rock fell from the roof, and ventilation raises were blocked, but the entire crew (17 men)-temporarily trapped-dug their way to the surface after 14 grueling hours. Their first glimpse of daylight exposed them to the unfathomable: A huge rockslide had thundered over their heads and crossed the valley.
Ice may have pulled the trigger. The winter of 1902-1903 had left a huge snowpack on Turtle's summit. April had been unseasonably warm, and much of the snow had melted to feed the mountain's summit fissures. Then, on the starlit night of April 28th, it froze hard...
A flow of rock
If the cause of the slide is cloaked in mystery, the movement of rock across the valley has proved even more difficult to describe in a way that meets universal acceptance. It is more than two kilometers from Turtle Mountain's summit to the farthest extent of the rockslide. Why didn't the falling rock simply land at the base of the mountain as would have been the case with the fall of isolated boulders?
Most scientists believe the rockslide flowed like a thick liquid-in contact with the ground and following its contours, even detouring around elevated areas. As evidence, organically stained sand testifies to the fact that at least some of the rockslide passed through the Crowsnest River and along the ground. But, how could rock flow?
There are various mechanisms which, individually or collectively may have been involved. These include: mechanical vibration, acoustic fluidization (creation of a sound with just the right pitch and intensity to cause the rock to flow), propagation of kinetic energy (transfer of momentum by collision of rocks), granular flows (in which the rocks on the bottom of the mass absorb most of the friction, while the bulk of the material, slightly elevated, moves forward as a solid mass-much like a car on wheels), and the entrapment of fluidizing agents (steam, air, water, dust, or mud).
It has also been hypothesized that the rockslide was not in consistent contact with the ground, but rode on a thin layer of air which had been trapped when the falling rock-in contact with the mountain-hit a projecting shelf near the base of the slope and was launched above the valley floor. The mass, riding trapped air, is speculated to have traveled east until it ran out of gas.
Regardless of the means through which the rockslide moved downslope and across the valley, the Frank Slide continues to attract attention from scientists and the countless motorists who travel Highway 3 through the Crowsnest Pass-the lowest trans-Rocky Mountain pass between New Mexico and Jasper National Park.
The University of Waterloo's "new" boulder comes with a storied past. Its presence is sure to promote historical reviews and spark future debates-facts which should please Peter Russell. About the writers: B. Monica Field manages the Frank Slide Interpretive Centre in the Crowsnest Pass and David M. McIntyre is an Alberta writer, photographer and naturalist who lives in the Crowsnest Pass.