Gravitational instabilities such as debris flows and landslides play a key role in erosion processes and represent one of the major natural hazards threatening population and infrastructures all over the world. They are also closely related to volcanic, seismic, and climatic activity and thus represent potential precursors or proxies for the time change of these activities.

One of the ultimate goals of research on gravitational mass flows is to produce tools for detection of landslides and for prediction of their velocity and runout extent. The theoretical description and physical understanding of these processes are extremely challenging problems. In recent years, significant progress in the mathematical, physical, and numerical modelling of gravitational flows, as well as advances of monitoring techniques, have made it possible to develop and use numerical models to investigate process dynamics and assess associated risks. However, key questions still remain unanswered, for instance concerning the reason for the high mobility of natural landslides.

Two severe limitations prevent a full understanding of landslide dynamics. First, the mechanical behavior (rheology) of these flows is still an open issue and the resulting mathematical and numerical models are oversimplified and not always well-posed. In particular they do not take into account complex natural phenomena such as interaction of fluid and solid phases, cohesion or fragmentation. Secondly, field measurements relevant to the dynamics of natural landslides are scarce due to the unpredictability and destructive power of such events, making it nearly impossible to validate the description of the physical processes in the models. In this context, the analysis of the seismic signal generated by these instabilities provides a unique tool to recover information on flow dynamics.

The Advanced School provides an overview of the state-of-the-art in these different fields going from the behavior of granular material involving cohesion, fragmentation, presence of a fluid-phase up to the behavior of landslides at the field-scale and their interaction with climatic, seismic, volcanic, and human forcing. The courses will span from theoretical work on granular flow models, experimental work on granular flows, discrete and continuum simulations up to field measurements as well as inversion of the generated seismic waves. A focus will be made in each field on the limitations and complementarity of the different approaches and on the open issues.

Two poster and brainstorming sessions dedicated to:
1) physics and rheology of lab-scale granular flows;
2) measurements and simulation of field-scale landslides.

The brainstorming sessions will more particularly address the two challenging issues, which play a key role in the description of natural gravitational flows:
1) What are the limits of the current rheological laws such as μ(I) when applied to describe transient flows?
2) Which processes can be at the origin of the unexplained high mobility of natural landslides?

We expect that confronting the different and possibly contradictory points of view of the speakers and assembly on these issues will make it possible to identify original research directions in physics, mechanics, modelling and field measurements.

The Vajont field trip will focus on the biggest landslide-related disaster in Italian modern history. On October 9th, 1963, a devastating landslide occurred in the valley of Vajont, Italy. After filling the reservoir behind a recently built dam, around 250-300 Mm³ of rock and debris detached and slit into the reservoir. The resulting flood wave overtopped the dam and destroyed settlements and infrastructure along the way, causing more than 2,000 casualties. During the field trip we will visit the dam and the landslide as well as the Museo Longarone Vajont.