In this chapter I show that it is possible to identify across a range of different thinkers a shared analytical investment in collective behaviour that allows one to distil the notion of social avalanches or social avalanching. The fundamental claim I make is that Durkheim, Simmel, Tarde and many others sought to respond to an experience that gained particular prominence in the late nineteenth and early twentieth centuries: various forms of social change increasingly produced situations in which individuals felt the ground disappearing beneath them, carrying them away in a collective turbulence which, once set in motion, acquired its own self-organising properties. In addition to developing the notion of social avalanching from late-nineteenth-century social theory, this chapter explores the prosocial character of avalanches. Elaborating on the concept of social avalanching, I examine the extent to which a metaphor such as ‘avalanche’ merits inclusion in the realm of proper sociological concepts and connect it to discussions within physics about self-organised criticality. Finally, I discuss the notion of social avalanching in relation to social action as conceived in the sociology of Max Weber.