A 36Cl age determination for Mystery Creek rock avalanche and its implications in the context of hazard assessment, British Columbia, Canada

Abstract

A 36 Cl age determination for Mystery Creek rock avalanche and its implications in the context of hazard assessment, British Columbia, CanadaAbstract The Sea to Sky Corridor has experienced hundreds of historic and prehistoric landslides. The most common types of historical landslides are rock falls and debris flows, which are relatively small in volume but can be damaging. These types of failures are more common in the southern part of the corridor, between Horseshoe Bay and Porteau, where infrastructure has been built in close proximity to steep slopes. Farther north, fewer landslides have been reported historically, but those that have been recorded are usually large and date to prehistoric time (e.g., Cheekye fan and Mystery Creek rock avalanche). As part of a Geological Survey of Canada surficial geology and landslide inventory mapping study, Mystery Creek rock avalanche, near Whistler, British Columbia, was sampled for 36 Cl dating. Samples were collected from three large flat boulders of quartz diorite in the rock avalanche deposit to test a correlation with the previously reported radiocarbon age of 800±100 years BP on charcoal. One sample revealed a mean age of 2,400years and the other two, 4,300 and 4,800 years, respectively. These new results point to four possible interpretations: (1) Mystery Creek landslide is about 800years old; (2) Based on the overlapping 2σ uncertainties, the rock avalanche took place between 2,200 and 3,600 years ago; (3) The rock avalanche deposit is 2,400 years old and the other two blocks are too old; and (4) The rock avalanche is between 4,300 and 4,800 years old. Although there is strength in numbers and it is likely that the age varies between 4,300 and 4,800years, we favor the second interpretation where the age range is broader and statistically significant for all three samples. Moreover, at this time, we favor discounting the radiocarbon age based on a greater number of samples analyzed for 36 Cl analysis and lack of detailed information on the charcoal sampling. The causes and triggers of the Mystery Creek rock avalanche remain unknown, but direct glacial debuttressing can be ruled out. Some of the causes are likely a combination of the regional tectonic setting which produced preferential planes of weakness reflected in the trend of major faults, headscarp, and reverse scarps. Yearly cycles of freezing and thawing are considered a plausible cause based on present-day climate records. Finally, a large earthquake still remains a possible trigger because of the active tectonic setting and the presence of potentially contemporaneous landslides in the same area. Mystery Creek rock avalanche and other historic and pre-historic landslides contributed to validation of a heuristic rock fall/rock slide/rock avalanche susceptibility mapping study, in which their headscarps correlated well with medium-high to high susceptibility zones. In terms of hazard assessment, Mystery Creek rock avalanche, although pre-historic in age, occurred in present-day climatic and geological condit...

Diagnostic characteristics and paleodynamics of supraglacial rock avalanches, Innerdalen, Western Norway

“…Its application to landslide research (Ballantyne et al, 1998;Hermanns et al, 2001Hermanns et al, , 2004Ivy-Ochs et al, 2009;Sturzenegger et al, 2014) is useful for landform interpretation and to determine temporal distribution of landslide events, correlate their occurrence with climatic changes (Ballantyne et al, 2014), assess realistic frequencies for similar events and conditions (Blais-Stevens et al, 2011), and determine long-term slide velocities of slow-moving rockslides (Hermanns et al, 2012b).…”

“…Large boulders were chosen to minimize the effect of influencing factors on TCN production and age calculations, such as snow cover, vegetation, post-depositional movement, and exhumation of a boulder through a moraine by erosion of a till or heaving of the boulder. Additional measurements were taken to adjust for other factors, such as topographic shielding of the cosmic-ray flux and geometric effects, for example, surface dip and proximity to the boulder edge (Blais-Stevens et al, 2011;Hermanns et al, 2012b). The positions (latitude and longitude) of the sampling sites were determined in the form of UTM coordinates (Zone 32) with a handheld GPS device (accuracy 5-10 m) and converted to decimal degrees.…”

36 Cl terrestrial cosmogenic nuclide dating suggests Late Pleistocene to Early Holocene mass movements on the south face of Aconcagua mountain and in the Las Cuevas–Horcones valleys, Central Andes, Argentina

“…Excellent summaries of this method were published by Lal (1991), Cerling & Craig (1994), Kurz & Brooke (1994) and Gosse & Phillips (2001) and the method has been repeatedly used for dating mass movements (e.g. Ballantyne et al 1998;Hermanns et al 2001Hermanns et al , 2004Bigot Cormier et al 2005;Dortch et al 2009;Antinao & Gosse 2009;Welkner et al 2010;Blais-Stevens et al 2011, and references therein). Here, we briefly review only the methods of sampling, principles of the method and correction factors, as they require some special considerations.…”

“…This is necessary because we cannot know if a boulder of 5-10 m length and 10-15 m width is indeed snow-free if it overtops the surrounding area by the snow depth. Thus, we estimate an uncertainty due to snowdrifts by calculating the age without snow cover and a maximum estimated snow cover (Tables 1 & 2) following the principle outlined in Blais-Stevens et al (2011). The resulting difference is significant and amounts to as much as 15 percent of the age.…”

Reconstruction of the history of the Palliser Rockslide based on 36Cl terrestrial cosmogenic nuclide dating and debris volume estimations

“…Ballantyne et al (1998) compared the age of a landslide with deglaciation in Scotland. Blais-Stevens et al (2011) dated the Mystery Creek rock avalanche in Canada. Antinao and Gosse (2009) used TCN to constrain a regional chronology of the Southern Central Chilean Andes rockslides and their associated sediment flux.…”