Abstract Distinctive suites of landslides occur in five stratigraphic-structural provinces in the Foothills area of southwestern Alberta. The Porcupine Hills are characterized by slumps and earthflows on slopes steepened by fluvial activity. The ridges of the Rocky Mountain Foothills have a low frequency of landsliding due to slope angles that are generally lower than bedding-plane dip angles. Extensive landsliding around the Mokowan Butte upland is likely due to shearing of bedrock beneath the Lewis thrust and glacial oversteepening. Glaciolacustrine valley fills form the floors of interridge valleys within the Foothills. These glaciolacustrine sediments fail as rotational slumps and flows. Rockslides and rock avalanches cluster along major thrust faults in the eastern Rocky Mountains. Glacial steepening and the exposure of cliff-forming Proterozoic and Paleozoic carbonates and clastics overlying recessive clastics, particularly along thrust faults, are identified as significant destabilizing factors. A mass-wasting feedback loop is suggested, cliff-forming massifs driving failure in underlying recessive rocks, which in turn triggers failures in the massif. Creep is suspected as a factor in footwall slope instability. Landsliding has likely been a prime agent in the retreat of the mountain front for at least the past 2.6 m.y. Recession rates of 0.2 cm/yr can be computed for this period.

Abstract Large slope failures in fractured rocks are often controlled by the combination of pre-existing tectonic fracturing and brittle failure propagation in the intact rock mass during the pre-failure phase. This study focuses on the influence of fold-related fractures and of post-folding fractures on slope instabilities with emphasis on Turtle Mountain, located in SW Alberta (Canada). The structural features of Turtle Mountain, especially to the south of the 1903 Frank Slide, were investigated using a high-resolution digital elevation model combined with a detailed field survey. These investigations allowed the identification of six main discontinuity sets influencing the slope instability and surface morphology. According to the different deformation phases affecting the area, the potential origin of the detected fractures was assessed. Three discontinuity sets are correlated with the folding phase and the others with post-folding movements. In order to characterize the rock mass quality in the different portions of the Turtle Mountain anticline, the geological strength index (GSI) has been estimated. The GSI results show a decrease in rock mass quality approaching the fold hinge area due to higher fracture persistence and higher weathering. These observations allow us to propose a model for the potential failure mechanisms related to fold structures.

Abstract This guidebook chapter outlines a walking tour that provides an introduction to the geological, archaeological, and historical setting of Pittsburgh, with an emphasis on the use of local and imported geologic materials and resources in the eighteenth and nineteenth centuries. The focus is on downtown Pittsburgh, the low-lying triangle of land where the Monongahela and Allegheny Rivers join to form the Ohio River, and Coal Hill (Mount Washington), the escarpment along the Monongahela River to its south. Topics include the importance of—and concomitant effect of—historic coal use; use of local and imported geologic materials, including dimension stone used for buildings and gravestones, and chert used for gunflints and millstones; the frontier forts built at the site; and the ubiquitous landslides along Coal Hill.