This paper uses a case study from Latin America to investigate the geological politics surrounding borderland volcanoes. As scientific technologies for volcano monitoring improve, and the number of volcanoes monitored globally increases, a growing awareness of transborder volcanic risk is developing. In parallel to this, developments in geopolitics have started to embrace the idea of vertical territory: territory as a material volume, re-emphasising the geological in politics and the political in geology. This paper considers the dynamics of territory through time, with a particular focus on extreme “geo-events” that reshape institutions, reveal cross-border differences in nation-state assemblages and redistribute the earth in dynamic ways. This raises interesting challenges for scientists because of the diverse scientific histories and institutional structures between nations, but it also raises potential geopolitical challenges. The paper thus argues that volcanoes can provide focal points for the politics of the geos, as experienced by communities and by scientists: awareness of “the other” side of the volcano-border, and experiencing the activity of the earth in a liminal setting is important in how people interpret the earth and their own identities. Volcanic eruptions highlight the diversity of institutional approaches across the border, and can provoke reconfiguration of national priorities.