The Frank Slide Story
At 4:10 a.m. on April 29th, 1903, 82 million tonnes of rock fell from
the summit of Turtle Mountain into the Crowsnest River valley below.
The slide lasted a mere 90 seconds and in that short time at least
90 people were killed – Canada’s deadliest rockslide.
At the southeast
edge of the small coal mining town of Frank, buildings were on fire and
survivors called for help. Despite the obvious devastation, the pre-dawn
darkness hid the magnitude of the event from the people of the Crowsnest
Pass – then a clustered grouping of coal mining communities in the Canada’s
Northwest Territories – today part of the Municipality of Crowsnest Pass
in the southwestern corner of the Province of Alberta.
The rockslide
buried the eastern outskirts of the town. It also obliterated a two kilometre
stretch of the Canadian Pacific Railway, surface buildings of the Canadian
American Coal and Coke Company, two ranches, a portion of the Frank and
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 literally a stone's throw beyond the area
buried. Just over one hundred people were in the direct path of the slide,
and twenty-three of those, in cottages on Manitoba Avenue along the western
edge of the slide, escaped death.
Early Warning
It was local rancher Louis O. Garnett who gave Turtle Mountain
its name - derived from what was envisioned as the outline of a turtle
shell along the summit ridge of the mountain. Prior to Garnett’s naming
of the mountain, it had been reported that the native peoples of the
area, the Blackfoot and K’tunaxa, had oral traditions which referred
to the peak as "the
mountain that moves." Supporting these statements, it is said that
they did not camp in the area that was subsequently impacted by the slide.
Almost certainly, the prehistoric people who mined chert, or flint, across
the valley as much as 5000 years ago and left pictographs near timberline
on adjacent Bluff Mountain had traversed Turtle Mountain's crest, where
it is believed that they would have seen the massive cracks and fissures
along the summit ridge. They may also may have observed seasonal rockfalls.
Causes
of the Slide
The primary cause of the Frank Slide was the mountain's unstable
geological structure. During the later stages of the creation of the
Rocky Mountains, which was active in the vicinity of Turtle Mountain
some 70 to 65 million years ago, beds of Paleozoic carbonates from the
Rundle Group (300-350 million years old) were "thrust" to the
east along the Turtle Mountain Thrust Fault to create the mountain. These
deposits overrode structurally weaker, nearly vertical, Mesozoic deposits
of sandstone, siltstone, shale, conglomerate and coal.
The mountain building
process also deformed the beds of Paleozoic carbonates, folding these
sedimentary deposits into the arched form of the Turtle Mountain Anticline.
The force of gravity caused slippage and movement along bedding planes
– the zones between the layers of sedimentary rock. Removal of rock layers
through erosion and the subsequent release of pressure caused fractures
to open up along the top of the mountain. Through the large summit cracks
water was able to access the mountain’s core. Water within the mountain
reduced cohesion – particularly along bedding planes between sedimentary
layers – and dissolved the limestone.
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
in length) and Gargantua (six kilometers) – which were created during
past millenia 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 that continue to erode and enlarge
the limestone caves through which they flow. Turtle Mountain has a small
cave near its South Peak summit and a sulfur spring, which continues
to "eat" the mountain's foundation beneath
North Peak. The constant 9.1° Celcius spring flows year round at a rate
of 450 liters/minute.
By the time mountain building had concluded, Turtle
Mountain's summit and eastern face had significant cracks. Beneath the
surface fissures – beneath almost the entire mountain – was the Turtle
Mountain Thrust Fault. Water continued to drain 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 what was now an inevitable rockslide.
During periods of glaciation, valley glaciers carved through the Rockies,
separating Turtle Mountain from Bluff Mountain, its twin sister to the
immediate north.
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 strata
– the mountain's Paleozoic "shell" - and exposed its weaker
Mesozoic foundation. The eventual retreat of the valley ice exposed the
severely weakened eastern base of the Turtle Mountain Anticline. It left
the top of the mountain without adequate structural support. Turtle Mountain’s
eastern face was, in effect, was "left hanging" high above
the valley.
Similar conditions have existed elsewhere in the Rocky Mountains,
and the Frank Slide is but one of an estimated one thousand rockslides
to have occurred during the past ten thousand years. However, unlike
the cascades of rock which fell elsewhere and had no effect on the human
population, the Frank Slide would make history as Canada’s deadliest
rockside.
While Turtle Mountain's weak internal foundation and the effects
of glaciation had set the stage for structural failure, the mountain
was to receive yet another strategic attack: mining. Glaciation had exposed
seams of high quality coal within Turtle Mountain and turn-of-the-twentieth-century
entrepreneurs were quick to exploit it due to its proximity to the Crowsnest
branch of the Canadian Pacific Railway which was completed in 1898. Coal
from the Frank Mine was removed by excavating enormous underground chambers
for almost two kilometres inside Turtle Mountain. Between 1901 and April,
1903, more than a quarter of a million tons of coal were removed from
the Frank Mine. Later, many would claim that it was the removal of too
much coal that caused the Frank Slide to come down.
Although coal mining
within Turtle Mountain undoubtedly had an effect on the timing of the
slide, scientists believe that the top of the mountain would have given
way and the slide would have come down at some point in time. And there
is evidence that in the months leading up to the slide that the mountain
was foreshadowing the catastrophic events to come. Unfortunately, the
miners were not able to interpret these signs.
Men working underground
at the Frank Mine had reported strange movements as much as seven months
prior to that fateful morning of 1903. Large timbers holding up the roof
were cracking much more often than normal – a sign that there was increasing
pressure in the layers of rock. Miners on the morning shift often found
that overnight the coal had "mined
itself" and had fallen from the face. There were times, usually
during the early morning hours, when the floor of the mine pitched as
if it were a ship rocked by an ocean wave – again a sign that the rock
layers within the mountain were shifting. Amazingly, 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 seventeen men on night shift were safe inside the mine. They were
much safer than the men outside the mine who were crushed by the falling
rock. The seventeen miners were trapped inside the mine, but managed
to dig their way to the surface after thirteen 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 been
the trigger that set off the slide on that tragic night. March of 1903
had left a heavy snowpack on Turtle Mountain's summit. April of 1903
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 – down to -18°C. People later said that the night the slide
came down was the coldest night of the winter – quite unusual for late
April. Water in the summit cracks froze, expanding as ice and creating
a giant wedge that forced an enormous block of rock away from the mountain’s
face. The giant block has been estimated by scientists to be one kilometre
wide by almost half a kilometre high and 150 metres deep. Rock avalanched
from the mountain peak into the valley below. The roar was so great that
it is said that the slide could be heard two hundred kilometres away.
The entire event lasted a mere 90 seconds, with three square kilometres
of the valley bottom covered by rubble to an average depth of 15 metres.
A Flow of Rock
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
at the base of the slide debris 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 rock particles), granular flow
(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.
More info
Last reviewed/revised: May 8, 2012
