Understanding of basaltic eruption dynamics and mechanisms : effusive and explosive eruptions in Hawaiʻi

Hawaiʻi is viewed as the “type example” for many fundamental basaltic volcanic phenomena (Garcia, 2017). The extensive geophysical and visual monitoring network maintained by the Hawaiian Volcano Observatory (HVO) (Guffanti et al., 2010) allows for numerous basaltic eruption styles and their products to be described in great detail. Hawaiian volcanoes are famous for effusive eruptions and they are mainly built of pahoehoe and a’a lavas. However, two Hawaiian volcanoes, Kīlauea and Mauna Loa, have been the location of numerous examples, both historical and modern, of other low intensity basaltic eruptive styles. These include Hawaiian-style fountaining, persistent lava lake activity and rootless littoral cone eruptions (Heliker et al., 2003; Jaggar and Finch, 1924; Moore and Ault, 1965; Orr, 2008; Patrick et al., 2016). The products of such activity are rarely preserved in the rock record, and yet they are a common and typical part of these volcanoes’ long-term behaviour and provide valuable constraints on fundamental dynamic processes. Three case studies of such ephemeral eruptive activity, each focussed on a different phenomenon, are presented in this thesis: five episodes of Hawaiian-style fountaining in the 1983-present eruption of Puʻu ʻŌʻō on Kīlauea, the 2010-2018 stable Halemaʻumaʻu lava lake at the summit of Kīlauea, and the rootless littoral cones at Puʻu Kī and ʻAuʻau Point on Mauna Loa. These studies provide a better understanding of the full spectrum of activity typical of basaltic volcanoes. Tephra from the early Hawaiian fountaining episodes of the ongoing eruption of Puʻu ʻŌʻō in the East Rift Zone (ERZ) of Kīlauea provides an opportunity to study the vesicle microtextures of pyroclasts erupted from a single vent over a prolonged period of time. The results of microtextural analysis of pyroclasts from five of Puʻu ʻŌʻō’s high (>200 m) Hawaiian fountaining episodes (episodes 32, 37, 40, 44 and 45) erupted during 1985–1986 are reported. The aims of the research are to constrain the parameters that led to large variations in fountain height at Puʻu ʻŌʻo, and the extent to which pyroclast residence times in the fountain modified microtextures. The results confirm the finding of Stovall et al. (2011, 2012) that pyroclasts from a single Hawaiian fountain can vary greatly in texture (from bubbly to foamy) and have vesicle volume densities (N\(^m\)\(_v\)) and vesicle to melt ratios (V\(_G\)/V\(_L\)) that vary by an order of magnitude. Pyroclast microtextures can range from high density (typically >500 kg m\(^{-3}\)), high N\(^m\)\(_v\) (2.2×10\(^6\) to 4.4×10\(^6\)), low V\(_G\)/V\(_L\) (2.06 to 4.65) bubbly textures to low density (