Petrology as a Volcano-Monitoring Tool: Can Magma Tell Its Story in Time to be Useful?

Abstract:

Changes in lava chemistry that both reflect magma-plumbing complexities and affect eruptive behavior occur during many volcanic eruptions. Standard geochemical techniques are typically considered too slow to contribute to hazard monitoring during a crisis. In 2018, the lower East Rift Zone (LERZ) of Kīlauea Volcano erupted about a cubic kilometer of lava in three months, with devastating effects on several communities on the Island of Hawaiʻi. We developed a rapid-analysis protocol to measure diagnostic elements in lava within a few hours of sample collection throughout the LERZ eruption. Geochemical data and Mg- and Ca-geothermometry provided important information for field crews and civil authorities in advance of changing hazards during the eruption.

At least three different sources of magma fed the eruption. The first two were primarily derived from distinct pockets of residual magma stored in Kīlauea's East Rift Zone for at least 58 years. They were composed of chemically evolved lavas, producing small volume, relatively cool, and slow-moving flows. One fissure even resulted in unusually explosive eruptions of a highly viscous andesite bearing enclaves of crystal mush. The third and dominant source was more-primitive tholeiitic basalt, transported from the draining rift-zone and summit magma reservoirs. The appearance of this hotter magma was recognized geochemically several days before the onset of voluminous effusion of fast-moving, lower-viscosity lava flows that destroyed hundreds of homes. Its arrival also corresponded with distinct changes in seismicity and deformation related to dike opening. Lava erupted during this phase was initially dominated by lower temperature, shallow-stored magma that was gradually replaced by hotter magma from the deeper summit reservoir.

Geochemical analyses of lava samples in near-real time contribute critical information about magma plumbing, transport, and mixing that enhances hazard assessments and risk mitigation during eruptions. The successes and challenges encountered during this crisis led to improvement of protocols, which could make petrologic analysis a more common and valuable tool used to monitor volcanic eruptions.