A combined remote sensing – numerical
modelling approach to the forensic investigation
of three large, catastrophic rock slope failures
A. Wolter, D. Stead, J.J. Clague, M. Havaej, & J. Vivas-Becerra
Simon Fraser University, Burnaby, British Columbia, Canada
ABSTRACT
Significant advances have been made in the study of complex rock slope failures, particularly in remote sensing and
numerical modelling. We investigated the preconditions, initiation, kinematics, and dynamics of three famous rock slope
failures using long-range terrestrial digital photogrammetry, thermal imaging, and sophisticated two- and threedimensional numerical models. The 1963 Vajont Slide in northeast Italy involved failure of a 250 million m 3 carbonatedominated sequence into the newly created Vajont Reservoir. The slide mass generated a wave that overtopped Vajont
Dam and flooded the valley below, killing 1910 people. The Madison Canyon Slide in 1959 was triggered by the largest
historic earthquake (M 7.5) in the Rocky Mountains and involved 20 million m3 of schist and gneiss and a stronger
dolomitic marble that buttressed the toe of the slope prior to the earthquake. The landslide dammed Madison River,
forming Earthquake Lake, and killed 24 people. Finally, the 2010 Mount Meager landslide involved about 48 million m 3 of
rhyodacitic flows and pyroclastic rocks of a Plio-Pleistocene volcanic complex in southwest British Columbia. A rock slide
transformed into a debris flow that travelled 10 km down Capricorn and Meager creeks to Lillooet River. The failure is
one of the largest landslides in Canada and dammed both Meager Creek and Lillooet River, but no lives were lost.
We characterised the largely inaccessible rock masses in the source areas of each landslide, as well as the debris at
Vajont and Madison Canyon, using photogrammetry. Photomodels created using f = 20, 50, 100, 200, and 400 mm focal
length lenses captured features at different scales, and allowed us to measure and characterise discontinuity orientations
and persistence, lineation trends, and failure surface roughness and morphology. Thermal imaging at Mount Meager
provided additional information on structures in the source area and is an important emerging technique for rock slope
characterisation. Using input from previous literature, field work, and remote sensing, we applied a numerical toolbox to
the Vajont and Madison failures to further study their behaviour. The continuum codes Phase2 and FLAC3D and latticespring code Slope Model highlighted in situ stress distributions due to landscape evolution, internal deformation of the
failing masses, and the development of a Prandtl wedge transition zone between the active and passive blocks of each
landslide. The discontinuum codes UDEC and 3DEC were used to examine the effects of discontinuity orientation and
block size on the kinematics of each failure. Preliminary groundwater and dynamic simulations provided insights into the
triggers at Vajont and Madison Canyon – reservoir level fluctuations and seismicity, respectively.