Thermoporomechanics of creeping landslides: The 1963 Vaiont slide, northern Italy

The catastrophic Vaiont landslide (Southern Alps, Italy) of 9 October 1963 moved 2.7 × 108 m3 of rock that collapsed in an artificial lake, causing a giant wave that killed 1917 people. The landslide was preceded by 2-3 years of creep that ended with the final collapse of the rock mass slipping at about 30 m s-1. Assuming that creep was localized in a clay-rich water-saturated layer, in this study we propose shear heating as the primary mechanism for the long-term phase of accelerating creep. We study only the creeping phase of the slide, and we model this phase using a rigid block movig over a thin zone of high shear strain rates. Introducing a thermal softening and velocity strengthening law for the basal material, we reformulate the governing equations of a water-saturated porous material, obtaining an estimate for the collapse time of the slide. Our model is calibrated upon real velocity measurements from the Vaiont landslide and provides an estimation of the critical time of failure up to 169 days before the collapse. We also show that the slide became critical ∼21 days before the collapse, when shear heating started localizing in the clay-rich layer, inducing a tendency for slip localization and thermal runaway instability in a plane. The total loss of strength in the slipping zone during the last minutes prior to the slide is explained by the onset of thermal pressurization, triggered by the temperature rise within the clay-rich layer. Copyright 2007 by the American Geophysical Union.