Science is often considered a master of certainty with privileged access to nature. However, when it comes to volatile and highly unpredictable environments like volcanoes (earthquakes, tsunami’s, and landslides too) science operates in murkier territory. This talk will focus on selected episodes in the history of science on Mt. Merapi in the twentieth century. It will ask questions such as: what does it look like to ‘know’? How is it performed? Is certainty just an effect of technological devices and tools, the real masters of truth? What is the role of the fragile human body in volatile environments?