This article presents a musicological and ecocritical close reading of the song "Brennisteinn" ("sulphur" or, literally, "burning rock") by the acclaimed post-rock band Sigur Rós. The songand its accompanying music video-features musical, lyrical, and audiovisual means of registering the turbulence of living in volcanic landscapes. My analysis of Sigur Rós's music opens up a window into an Icelandic cultural history of inhabiting a risky Earth, a condition captured by anthropologist Gísli Pálsson's concept of geosociality, which emerged from his ethnography in communities living with volcanoes. Geosociality allows for a "down to earth" perspective that accounts for the liveliness of the ground below our feet. Likewise, in Sigur Rós's "Brennisteinn", we encounter a musical imagination of the geologic that poses a challenge to hegemonic concepts of nature founded on notions of equilibrium and permanence. The article culminates with a consideration of what such a geologically minded aesthetics can offer us in the age of the Anthropocene.