Weathering as a predisposing factor to slope movements: an introduction

Recognition of weathering as a primary process in the development of landforms dates back at least to the late 19th and early 20th century, as indicated by several contributions from various countries (e.g. Cortese 1895; Branner 1896; Falconer 1911; Jutson 1914; Walther 1915); nevertheless, it was only in the second half of the last century that systematic studies on weathering and related topics such as geomorphology, engineering geology and petrography were carried out. In a recent review paper Ehlen (2005) found through an on-line search more than 9000 hits where the term ‘weathering’ was used, dating from the mid-1950s to the beginning of the 21st century. Such a huge number of citations clearly demonstrates the attention that the scientific community has dedicated to the in-place breakdown of rocks by chemical, physical and biological processes. However, despite the high frequency of landslides and erosional phenomena in weathered materials, and the damage and casualties they repeatedly cause, not very much is known about the direct and indirect relationships between weathering and slope movements. The matter is further complicated by the high variability of landslide features (Working Party on World Landslide Inventory 1993). According to the local conditions, a variety of slope movements may take place in the weathered rock masses. Shallow soil slips evolving to rapid and catastrophic debris flows are probably the most common type in steep residual soil slopes, whereas thicker failures, also including deep-seated complex movements, can affect large volumes of weathered rocks.Following the first, simplified attempts to classify slides in natural slopes of residual soils (e.g. Morgenstern & de Matos 1975; Vargas & Pichler 1975), Durgin (1977) provided a comprehensive scheme of the relationships existing between landslides and weathering (Table 1). In general terms, studies on weathering-related landslides showed that in the …