Mt. Merapi in Central Java is one of the worlds most active and populous volcanoes. It has roughly a million people living on its flanks and volcanic events occur every four to five years. As a site of permanent environmental instability, it is a case through which to consider more broadly applicable strategies for living with environmental uncertainty. My study focuses on the role of gatekeepers as they interface, make meaningful and negotiate the volcanic system. These gatekeepers are the *Juru Kunci*, scientists and community radio operators. The *Juru Kunci* (Indonesian for key holder or gatekeeper) is appointed by the Sultan in the plains below and conducts diplomacy between his realm and the world of gods inside the volcano. Scientists negotiate the volcanic system, the contemporary state and its emergency operations. Radio operators position themselves in relation to a history of flight from the lowland sultanates and colonial occupation and horizontal forms of disaster mitigation. I frame their divergent practices according to three conceptual preoccupations: agency, boundary work and controversy. Together these account for the role of the human in volatile material milieus.