CALORIMETRIC DETERMINATION OF LAVA CRYSTALLINITY: THE FISSURE 17 FLOW, KILAUEA 2018

In order to determine crystallinity of lava samples, petrographical estimates can be limited by sample heterogeneity, and by the difficulty of determining crystallinity of groundmass. An alternative approach is to measure the enthalpy of fusion of a sample using Differential Scanning Calorimetry (DSC). For samples with significant glass fractions, the magnitude of the glass transition peak can also be compared with the peak height obtained from remelted glass. Here we use calorimetry to determine the crystallinity and thermal budget of different magmatic end-members that were potentially involved in the 2018 eruption on Kilauea’s Lower East Rift Zone.

Of the 24 different fissures that erupted during the 2018 eruption, Fissure 17 erupted lava that was more silicic (icelandite), and more explosive, than any other segment. This has been attributed to mixing between juvenile mafic lava and an older, more evolved magma body (Gansecki et al. 2019 Science). However, inclusions within the Fissure 17 lavas are generally crystalline and mafic, suggesting that the hot juvenile mafic lava encountered both mobile intermediate magma, and cool immobile mafic magma, potentially left over from the 1955 eruption. Geochemical data can be used to infer mixing end-members, but hypotheses based on geochemistry can be tested with physical investigation of magma rheology and thermal budgets.