Mobility of pyroclastic flows and rock avalanches: a functional relationship of scaling parameters

Abstract

Flows of angular rock fragments are released down a concave upward chute in the laboratory to study their mobility which is measured considering the travel distance of the centre of mass of the granular masses. The prediction of flow mobility is necessary, in volcanic and mountain regions, to assess natural hazards caused by pyroclastic flows and rock avalanches. The longitudinal profile of our chute is similar to that of the flanks of Mayon volcano in the Philippines. Our flows are dry and they have different masses (30 and 60 g) and different grain size ranges (0.5-1, 1-2 and 2-3 mm). The values of all the other variables that can affect the travel distance are held constant. Flow mobility is measured as the reciprocal of the apparent coefficient of friction that is equal to the ratio of the vertical drop of the centre of mass to its horizontal distance of travel. Our dimensional analysis generates a functional relationship between the apparent coefficient of friction and a scaling parameter that contains grain size and flow volume.