 |
| Researchers set up monitoring equipment in an effort
to unlock the mysteries of Turtle Mountain, responsible
for the famous and tragic Frank Slide. |
Native lore calls it ‘the mountain that moves.’ Researchers
want to know how often and how much – and whether Turtle
Mountain is preparing a sequel to the legendary and deadly
Frank Slide of 1903.
BY BILL CORBETT
Freelance Writer
In the early morning of April 29, 1903, more than 90 million
tonnes of limestone slid from the east face of Turtle Mountain
and swept through a sleeping town in Alberta’s Crowsnest
Pass, killing an estimated 70 people. The Frank Slide,
named for the town it buried, quickly found purchase in
the public imagination as the most celebrated and fatal
landslide in North American history.
Although the mountain has been extensively studied and sporadically
monitored over the years, uncertainty remains over exactly
what happened – and if, or when, it might slide again.
To mark the 100th anniversary of the Frank Slide, the Alberta
Government announced last spring a $1.1-million program to
monitor every creak, groan and shift in the potentially unstable
rock mass on South Peak, one of the two prominent peaks left
on Turtle Mountain by the 1903 slide. The primary goal is
public safety – to better predict a future slide that
could threaten people and valley infrastructure.
But researchers are also improving their understanding of
landslides in general and the mountains that spawn them,
testing new technologies and educating a public still fascinated
by the story.
Shifting Technology
The program provides a perfect opportunity to deploy state-of-the-art
geotechnical and geophysical monitoring technology, some
of which was originally developed for oilfield monitoring,
notes one project researcher.
“Most of our research here is developing methods for
exploring hydrocarbons,” says Dr. Robert Stewart, P.Geoph.,
a geophysics professor at the University of Calgary who also
teaches a popular course in natural disasters. “One
of our technologies involves installing seismic monitors
over oilfields and monitoring the popping, cracking and fracturing
of petroleum reservoirs as they’re being produced.
“The same technology can be used to monitor fracturing
or micro-seismicity in Turtle Mountain.”
Last summer and fall, Dr. Stewart’s team began installing
a series of seismic monitoring stations on the mountain to
measure microseismic activity associated with such things
as vibrations, fracturing, and deformation of the rock mass.
Over a dozen other teams will be installing surface and subsurface
geotechnical and geophysical monitoring systems to measure
displacement, pore pressure, temperature, water outflow,
and climatic data. They’ll also conduct supporting
geological, satellite and photogrammetric studies.
The results from all the installed systems (including deformation
monitoring by an independent Iowa State University researcher)
are being wirelessly transmitted to the Frank Slide Interpretive
Centre, where they can be watched and analyzed in near real-time.
“The whole monitoring effort is
based on the idea that these events (landslides) have precursors.
We suspect Turtle Mountain
will give us some warning if something is going to happen – according
to aboriginal legend, it was known as the ‘mountain
that moves’,” says Dr. Stewart, an APEGGA councillor.
“To be successful, the monitoring has to be sustained
and continuous. We don’t know if something might happen
next week or in the next millennium. But we do know this
is a particularly unstable mountain.”
The Turtle’s Geology
But why is it unstable? As one would assume, part of the
answer lies in Turtle Mountain’s very make-up.
Limestone layers have been geologically squeezed into an
arch, or anticline, which is broken at the mountain’s
top into large fissures. Water percolates down through these
cracks, dissolving the limestone and increasing rock pore
pressure by freezing and then expanding.
In the process, the rock layers on the downward slope of
this anticline become like shingles loosely attached to a
roof – just waiting for something to tip the balance.
Scientists believe the excavation of coal at the turn of
the 20th century from the Frank Mine, which traverses the
toe of the mountain, might have helped trigger the Frank
Slide. Near the coal seam, the Turtle Mountain Thrust Fault
and a small, secondary fault were further destabilizing factors.
But scientists still speculate about what caused the Turtle’s
east flank to fail on such a massive scale or to slide so
far.
The Theories
An early theory was that the massive layers of rock slid
on a compressed cushion of air. Yet old run-out slides
on Mars have been observed, and there’s no atmosphere
there.
A more recent theory is acoustic fluidization. Large volumes
of material generate their own seismic or vibrational energy,
reducing friction and allowing for long run-outs, behaving
more like a fluid than a solid mass.
Whatever the cause, such slides are not peculiar to Turtle
Mountain. Historically, they’ve been quite common in
the Canadian Rockies; indeed, there is evidence of such a
slide in an overgrown area on nearby Bluff Mountain.
What makes the Frank Slide significant is its size and length,
and that it occurred in a valley crowded with people, coal
mines and a railway. Although the adjacent and intact South
Peak of Turtle Mountain is similarly unstable, the good news
is it poses less risk to humans and their interests.
“While it (South Peak) contains five million cubic
metres of rock of the same general structure, it’s
only one-sixth of the original slide’s volume,” says
Dr. Rodney Read, P.Eng., P.Geol. “In an extreme case,
the maximum probable run-out would reach Highway 3.”
Dr. Read is the Okotoks-based project engineer for monitoring
Turtle Mountain. Apparently, interest in the slide runs in
his family – Dr. Read’s great-great-uncle did
the first post-Frank Slide measurements in 1903. Interestingly,
the same uncle – David Alexander Stewart – may
be related to Dr. Robert Stewart, too.
More to Learn
And 100 years later, there’s still plenty for scientists
to learn, Dr. Stewart believes, about what makes Turtle Mountain
tick – or fall apart. “Monitoring landslides
is still new enough around the world that it is not strictly
an engineering solution,” he says.
“
A lot of the technology we’re testing here could be
used for monitoring everything from ice thickness on roads
to snow avalanches in the mountains. They all have similar
components.”
The effort to satisfy the public’s appetite for Frank
Slide information continues, too. Because data and images
from the Turtle Mountain monitoring equipment, weather stations
and video cameras will be accessible, visitors to the Frank
Slide Interpretive Centre and perhaps Internet users will
be able to follow and learn from the research.
Dr. Stewart says some of the program monitoring has already
been incorporated into U of C geophysics and geology courses.
The $1.1-million monitoring project covers some 20 months
and is being spread over 18 work packages. Much of the work
will take place in the summer of this year, including the
drilling of boreholes. Into those holes will go measuring
equipment such as micro-seismic sensors, inclinometers and
extensometers.
Longer-term funding is still undecided, as is the government
agency that will oversee the ongoing operation of the monitoring
system. Whatever happens, it seems that there’s little
doubt the Frank Slide will continue to intrigue scientists,
students and lay people alike for many years to come.
|
