TOPPLES ON UNDERDIP SLOPES IN THE HIGHWOOD-PASS, ALBERTA, CANADA

Sixteen topples up to 15 m thick are exposed on underdip slopes in the Highwood Pass, Alberta. Toppling modes are controlled by ratios of joint spacings to bedding thicknesses (block ratios), rock strength and topography. Block flexure topples occur where block ratios are less than 2, while block topples form where block ratios are larger than 2. Multiple block topples develop sliding surfaces which may fracture thin beds rather than follow discontinuities. Chevron topples are retrogressive, simple block topples whose rupture surfaces coincide with hinge surfaces which may also develop into sliding surfaces. Chevron topples form on slopes over 35-degrees and are typically less than 5 m thick. The development of sliding surfaces during block toppling may allow the displaced masses to become slides.