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A geochemical and physical investigation of the Kulanaokuaiki Tephra of Kīlauea volcano, Hawai‘i
Date
2025
Authors
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Journal ISSN
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Publisher
University of Delaware
Abstract
Kīlauea volcano is the youngest subaerial basaltic volcano on the Island of Hawai‘i and has both effusive and explosive eruptions. Kīlauea has had two periods of dominantly explosive activity: the more recent Keanakāko’i Tephra (1500 to ca. early 1800s) and the Uwēkahuna Ash (200 B.C.E. to 1000 C.E.). The Kulanaokuaiki Tephra (400 to 1000 C.E.) is the youngest member of the Uwēkahuna Ash and is found primarily on Kīlauea’s south flank. This dissertation explores the Kulanaokuaiki Tephra from source to surface over four projects. ☐ The varied preservation and geographic extent of Kulanaokuaiki Tephra Units exemplifies the difficulties assessing prehistoric tephra [Chapter 2]. Anticipated hazards and associated risk from explosive eruptions of Kīlauea are difficult to constrain due to the inconsistent nature of deposits. ☐ The relative influences of crustal and mantle processes for generation of the Kulanaokuaiki Tephra were determined using glass major and trace element chemistry [Chapter 3]. My modeling of this data suggests that the Upper-Kulanaokuaiki (Units 3, 4, and 5) melt was slightly oxidized, with low water contents, and stored shallowly. In addition to a main magma storage reservoir, I identify a high K2O and TiO2 melt. This composition repeatedly appears over Kīlauea’s past 2000 years, including the Unit 3 (900 C.E.; this study), Unit K2 of the Keanakāko’i Tephra (early 1800s; Garcia et al., 2018), and Kīlauea Iki (1959; Helz et al., 2020). Ratios of highly over moderately incompatible trace elements suggest that the melts provided to Kīlauea may have been generated from an increasing degree of melting over the time of the Upper-Kulanaokuaiki eruptions. ☐ Storage timescales and eruption initiation of the largest basaltic subplinian eruption from Kīlauea – the Kulanaokuaiki Unit 3 – were investigated using olivine phenocrysts [Chapter 4]. The major element compositions and zoning patterns of olivine phenocrysts indicate crystal growth from undercooling prior to re-equilibration, based on increases in near-rim CaO abundances. Storage timescales of <1 to 12 years based on Fe-Mg diffusion chronometry are relatively longer than those for other Kīlauea explosive and effusive eruptions. Additionally, complex profiles of lithium coupled to phosphorus reveal histories of both growth and diffusion. The absence of diffusive lithium zoning and lack of reversely zoned F-Mg profiles suggests that the Unit 3 eruption was not triggered by a late-stage magma mixing event and was likely driven by gas-driven filter pressing. ☐ To discern the roles of degassing and fragmentation on explosive eruptions, I characterized the deposits and tephra of Units 1, 3, 4, and 5 [Chapter 5]. The Unit 1 tephra, from a high-fountaining Hawaiian style eruption, may appear as a primary deposit in the field, but quantitative dynamic-imaging analyses reveal that it was likely post-eruptively rounded due to ground transport. The rounded, equant vesicles of juvenile Unit 1 pumice support the bottom-up fragmentation that is typical of Hawaiian style fountains. The subplinian Unit 3 deposit systematically changes from lithic- to juvenile- rich and has a clast vesicle shape progression from poorly sorted, irregular, interconnected vesicles to well sorted, rounded vesicles. These observations support bottom-up fragmentation. Pre- and syn-eruptive crystallization likely created an impermeable plug that allowed pressure to build before eruption. Thus, bottom-up fragmentation of basaltic magmas can lead to both fountain-style and subplinian scoria eruptions. A well-preserved summit locality of the Kulanaokuaiki Unit 4 starkly contrasts its preservation on the south flank, highlighting the importance of both physical and geochemically linking tephra deposits. The Kulanaokuaiki Unit 5 remains enigmatic.
Description
"At the request of the author or degree granting institution, this graduate work is not available to view or purchase until August 13 2027".--ProQuest abstract/details page.
Keywords
Hawaii, Magma, Volcano