Why was the Sunset Crater eruption so powerful? View Dr. Chelsea Allison's (AZ State Univ.) 53-minute video to understand the role of carbon dioxide gas.
Photo by Ted Grussing; Sunset Crater cinder cone in the foreground, the San Francisco Peaks mantled by clouds in the background.
Video ABSTRACT. The eruption of Sunset Crater in northern Arizona ca. 1085 CE is the most explosive basaltic scoria cone eruption yet documented. This anomalous sub-Plinian eruption with >20 km high plumes is the most recent of >600 monogenetic scoria cone eruptions over the past ~6 Ma in the San Francisco Volcanic Field along the edge of the Colorado Plateau. Recent study of melt inclusions in olivine phenocrysts from Sunset Crater has found high concentrations of CO2 and sulfur as well as evidence for an exsolved CO2 phase in the magma at ~15 km depth prior to the eruption. This exsolved CO2 phase was critical in fueling rapid magma ascent to produce the highly explosive eruption, perhaps analogous to mechanisms that drive silicic caldera-forming eruptions. While these very large volume silicic eruptions are known to have climatic effects, an explosive basaltic volcano with significant sulfur content like Sunset Crater can impact the atmosphere from eruptions of more modest volumes.
Dr. Allison is now at Butler University as a Post-Doctoral research associate.