With the rise of environmental concerns and the advent of the precautionary principle, disaster risk reduction has become a central issue in public policy. In this context, researchers and operators of monitoring networks of telluric phenomena are increasingly called upon by the authorities and the general public to intervene as experts. However, the transition from the practice of research to the situation of expertise is not without difficulty. In that respect, the case of volcanic risk in the Lesser Antilles arc is particularly revealing given the highly variable spatio-temporal scales that characterize it, the numerous actors spanning the entire spectrum of society, the intrinsic and considerable epistemic and aleatory uncertainties, its low recurrence rate compared to other risks, but also the considerable chain-link specificity of its impacts that can significantly effect small vulnerable island states embedded in the legacy of a complex history, regional, and international context. One of the difficulties—rarely addressed by researchers acting as experts and by researchers studying expertise situations—is the fragmentation of disciplines into different specialties. This issue can only be tackled by transcending traditional disciplinary boundaries. This article, written jointly by researchers in political science and in Earth sciences, illustrates how knowledge of the epistemological tensions that underlie Earth sciences can contribute to enriching the analysis of public action on the issue of risk management. Our reflection is illustrated by two case studies: the crisis associated with the phreatic eruption of La Soufriere in Guadeloupe (in 1976), and the crisis associated with the magmatic eruption of the Soufriere Hills Volcano of Montserrat (1995-ongoing). It reveals that the tools mobilized by politists—like the concepts of expertise, controversies, instruments of public action or even epistemic communities—cannot fully capture the plurality of knowledge and know-how developed by experts facing intricate problems. This observation is not unique to volcanic risks. Most of the phenomena that threaten our societies today require, indeed, to take into account a complexity that goes well beyond traditional disciplinary boundaries. Getting out of the disciplinary isolation is difficult. This is evidenced by the Intergovernmental Panel on Climate Change (IPCC) experts’ efforts over more than three decades to harmonize not only the contributions of different research communities but to articulate them to make them operational for international public policy. Yet, the analysis of public action can only enrich itself to make the bet of such a dialogue.