Although explosion may initiate volcanism of the type represented at central vents, it is not essential for continued activity. Nor is such violent action necessary even for the opening of central vents, as shown by the pit‐craters of Hawaii. These are genuine volcanic vents and yet are not rimmed with ash, tuff, or breccia, the normal products of explosion. On the other hand, the pit‐craters, like Kilauea and many other craters on islands and continents, were opened and kept open by fluxing magmatic gas, rising quietly. Quiet emanation of gas is the essential part of the mechanism that gives prolonged activity. But emanation from what? This is the ineluctable, chief problem of volcanology. The root of the volcano is the root of the mat