Since the occurrence of the Frank Slide in 1903, studies have identified
potentially unstable volumes on Turtle Mountain adjacent to the original
slide source. In the 1930's, a mass of 5 million m3, known as South
Peak, was identified as the most unstable. Limited monitoring was
carried out for close to 70 years. The monitoring system was upgraded
at the turn of the millennium, as part of a comprehensive risk management
program, concerning identified elements at risk in the valley. Intensive
monitoring has now been carried out for 6 years and an early warning
system implemented. With the acquisition of airborne LiDAR in 2005,
a computer based structural mapping tool, COLTOP, was applied to
better understand the structural controls on the Frank Slide, South
Peak and other portions of the eastern face of Turtle Mountain. Recent
studies by Jaboyedoff et al (2009), Froese et al. (In Press) and
Pedrazzini et al. (2008) have highlighted structural controls on
instabilities on the eastern face of the mountain that differ from
those previously known for both the South Peak and for another portion
of the mountain, Third Peak, which had not been identified in previous
studies. The computer based structural models were confirmed with
field structural mapping and a Sloping Local Base Level (SLBL) technique
was used to estimate scenarios implying different volumes of potential
future instabilities. To understand the level of activity of these
volumes, an expanded monitoring network was installed in 2007 and
2008. It is expected that these portions of the mountain are moving
at a very slow rate (sub-millimeter to millimeter per year) and conclusive
evidence as to the level of activity may take years to ascertain.
In order to better understand the extent of the potential impact
of the hazards posed by these various unstable volumes (scenarios),
dynamic runout analyses have been undertaken. A three-dimensional
dynamic model has been calibrated using the experience from the Frank
Slide and other regional rock avalanches and applied to the volumes
derived from the SLBL to better define areas that are potentially
susceptible to impact from landslides below the eastern face of Turtle
Mountain. The results will be used to improve contingency plans within
the hazard area.