A discussion of the mechanisms of explosive basaltic eruptions

Two contrasting models of the dynamics of explosive basaltic eruptions are in current usage. These are referred to as the rise speed dependent (RSD) model and the collapsing foam (CF) model. The basic assumptions of each model are examined, and it is found that neither model is flawed in any fundamental way. The models are then compared as to how well they reproduce observed Strombolian, Hawaiian and transitional eruptive behaviour. It is shown that the models do not differ greatly in their treatment of Strombolian eruptions. The models of Hawaiian eruptions are, however, very different from each other. A detailed examination of the 1983–1986 Puʹu ‘O’o eruption finds that the CF model is inconsistent with observed activity in a number of important aspects. By contrast, the RSD model is consistent with the observed activity. The issues raised in the application of the CF model to this eruption draw into doubt its validity as a model of Hawaiian activity. Transitional eruptions have only been examined using the RSD model and it is shown that the RSD model is able to successfully reproduce this kind of activity too. The ultimate conclusion of this study is that fundamental problems exist in the application of the CF model to real eruptions.