The Influence of Rainfall and Temperature on the Displacement Rates of Two Slow-Moving, Clayey Landslides

The paper compares experimental data of displacements obtained by inclinometer measurements in two landslides which occur in the same slope of the southern Italian Apennines, in the same clay formation, the Varicolored Clays (Upper Cretaceous—Lower Miocene). The landslides have very different sizes: the largest one reaches 40 m depth, the smallest is about 5–6 m deep. The two landslides are thought to have been triggered by different causes in different times, and it is observed that they underwent different morphologic evolution. Currently, they are both sliding on well-defined surfaces, in conditions close to the residual. Their yearly displacement rates, in the order of a few cm/year, have been almost constant in the last twenty years but the time trend of displacement exhibits important seasonal variations. Such variations are very different in the two landslides: the deep landslide accelerates in wintertime whereas the shallow one accelerates in summertime. A strong correlation has been shown to hold among displacement rates, pore water pressures and rainfall for the deep landslide. For the shallow one, a correlation seems to hold between air or surface temperature and basal displacement rate.