Airblasts caused by large slope collapses
Large slope collapses have been known to trigger extreme rushes of air loaded with projectiles (airblasts) capable of causing destruction and fatalities far beyond run-out of the rock mass. An appraisal of the likelihood of a destructive airblast should be a component of landslide risk assessments. Yet there is an absence of risk studies directly examining landslide-related airblasts. In this work we back-analyze an unreported airblast in the Sikkim Himalayas (India) and several other airblasts documented around the world. We explore the conditions a large slope collapse should meet to trigger a significant airblast, and we establish a semi-empirical relationship linking the potential energy in a collapse with airborne trajectory and the extent of the related airblast. The collapse of thousands or millions of cubic meters falling from a significant height results in a sudden release of energy (1011J to 1013J) and a high degree of comminution of rocks, causing a violent displacement of air. Average wind speeds of airblasts following impacts with airborne trajectory can be double the speed of rock avalanches. The size of the damage zone depends on the potential energy of the falling rock mass and can be amplified or reduced depending on how confined the valley is where the airblast occurs.