From the source area to the deposit: Collapse, fragmentation, and propagation of the Frank Slide

The combination of structural data from the source area and descriptive data from the deposit’s carapace, as well as remote sensing and statistical analysis, allows a better understanding of the collapse, fragmentation, and propagation processes of the Frank Slide rock avalanche. The in situ observed conservation of the stratigraphic sequence of the Turtle Mountain anticline’s normal limb in the deposit is interpreted as the consequence of the collapse mode, involving simple shearing of the mass accompanied by a rotational movement, i.e., a “simple shear” parallel to the topography, and a breakage of the hinge, followed by overthrusting of the normal limb on the inverse limb. Coherence between the block size distributions of the source area and the deposit carapace is interpreted as a demonstration of the primary control of preexisting fracturing on the fragmentation processes. Remote-sensing indexes allow us to uncover a priori hidden morphological features preserved on the surface of the deposit, i.e., longitudinal and compressional features, as well as lobes. Their location on the carapace provides evidence of lateral heterogeneity in the propagation, highlighted by three different types of propagation behaviors. This comprehensive study not only provides elements that contribute to an understanding of the Frank Slide rock avalanche, but it also provides insight into essential parameters to take into account in further modeling of these types of phenomena.