Landslide incidence and its relationship with climate in three river valleys in the Bearpaw Formation in southern Alberta

Landslide incidences on the Battle, Red Deer, and Bow Rivers were mapped in the Bearpaw Formation in southern Alberta, and the incidences on north- and south-facing slopes of the three river valleys were mapped as well. The results indicate that the incidences decrease from the Battle, to the Red Deer and to the Bow Rivers, and that incidences decrease from north-facing to south-facing slopes. Incidences on north facing slopes are significantly higher than on the south facing slopes on the Red Deer River and the Bow River.; Climate differences are regarded as the main cause of the difference in moisture conditions which in turn causes differences of landslide incidence among the three valleys since the valleys are in different climatic zones but have the same geological formation and similar postglacial histories. Differences in landslide incidence between north- and south-facing slopes are caused by microclimate. Microclimate is controlled mainly by direct short-wave radiation, which in turn controls potential evapotranspiration and Agro-Climatic Moisture Index (AgM Index) on differently facing slopes.; The moisture difference is further reflected in vegetation differences from valley to another and from north-facing and south-facing slopes in the study area. The vegetation characteristics of along different valleys and slopes of different aspect strongly support the moisture differences.; Slope angles under conditions of constant lithology are believed to be controlled mainly by moisture conditions. Average slope angles increase from the Battle valley, to the Red Deer and Bow valleys. Active slopes eroded by rivers are significantly steeper along the Bow River than along the Red Deer River. Abandoned slopes covered by colluvial materials along the three rivers are in a range 6.0 to 6.8°, which shows that materials along the three valleys involved in landsliding are similar.