The Rheological and Thermal History of Kilauea's 2018 Fissure 17 Eruption
Kilauea's Fissure 17 eruption of 2018 was an anomaly among the other 24 fissures that erupted in the Lower Eastern Rift Zone in that it erupted explosively. Fissure 17 compositionally is an icelandite (an Fe-rich, Al-poor andesite) with highly crystalline mafic inclusions of an unknown origin. The presence of mafic inclusions in the icelandite indicates that mixing between at least two different magma bodies occurred prior to the eruption. The aim of this study is to understand why and how this fissure could have erupted explosively by attempting to identify the origins of the mafic inclusions. Two hypotheses were formulated for the origins of the inclusions, either (i) the mafic inclusions resulted from the injection of hot juvenile basaltic lava into the cooler icelandite, likely the same juvenile lava as was erupting from the dominant Fissure 8, , or (ii) the mafic inclusions are cold, brittle inclusions of wall rock (likely formed in 1955) that were mixed into the hotter icelandite. To test the hypotheses, crystallinity estimates for the icelandite (~64-80%), mafic inclusions (~68-91%), and 1955 lavas (~58-89%) were obtained via differential scanning calorimetry. MELTS modelling was utilized to test temperatures associated with the crystallinity and equilibrium temperatures associated with mixtures of 50:50, 60:40, and 70:30 mafic inclusions to icelandite. The observation of angular inclusions, and better match between the calculated and modeled crystallinity, suggest cold 1955 lava as the origin for the mafic inclusions, although with the current dataset we cannot disprove that Fissure 8 could be their source.