Abstract
Silicic submarine volcanic eruptions can produce large volumes of pumices that may rise buoyantly to the ocean surface and/or sink to the seafloor. For eruptions that release significant volumes of pumice into rafts, the proximal to medial submarine geologic record is thus depleted in large volumes of pumice that would have sedimented closer to source in any subaerial eruption. The 2012 eruption of Havre volcano, a submarine volcano in the Kermadec Arc, presents a unique opportunity to study the partitioning of well-constrained rafted and seafloor pumice. Macro- and microtextural analysis was performed on clasts from the Havre pumice raft and from coeval pumiceous seafloor units around the Havre caldera. The raft and seafloor clasts have indistinguishable macrotextures, componentry, and vesicularity ranges. Microtextural differences are apparent as raft pumices have higher vesicle number densities (109 cm−3 vs. 108 cm−3) and significantly lower pore space connectivity (0.3–0.95 vs. 0.9–1.0) than seafloor pumices. Porosity analysis shows that high vesicularity raft pumices required trapping of gas in the connected porosity to remain afloat, whereas lower vesicularity raft pumices could float just from gas within isolated porosity. Measurements of minimum vesicle throat openings further show that raft pumices have a larger proportion of small vesicle throats than seafloor pumices. Narrow throats increase gas trapping as a result of higher capillary pressures acting over gas–water interfaces between vesicles and lower capillary number inhibiting gas bubble escape. Differences in isolated porosity and pore throat distribution ultimately control whether pumices sink or float and thus whether pumice deposits are preserved or not on the seafloor.
Highlights
Physical volcanology is rooted in the interpretation of volcanic products [Cashman and Sparks 2013; Martí et al 2018]
Microtextural data for giant pumiceous blocks (GP) and GP290 was taken from an extensive study of the giant pumice blocks by Mitchell et al (2019); the fragments selected for GP microtextural analysis were taken only from the modal density category of the density distributions, as some remotely operated vehicle (ROV)-sampled materials were limited, at lower vesicularity
GP blocks have a variety of morphologies and can exhibit very blocky, angular, and irregular exteriors [Fig. 2d–f]
Summary
Physical volcanology is rooted in the interpretation of volcanic products [Cashman and Sparks 2013; Martí et al 2018]. Our understanding of changes in eruptive styles, clast transportation and deposition mechanisms, and key physical parameters. In the deep-sea environment, large volumes of freshly erupted material can be missing from the proximal to medial geologic record due to the dispersal of clasts as pumice rafts during eruptions [Bryan et al 2012; Carey et al 2018] and the complex nature of submarine ash dispersal and settling [Stewart and McPhie 2004]. Conducting studies solely on the preserved proximal seafloor deposits may significantly underestimate eruption volume and mass eruption rate, skewing our understanding of deep-sea volcanic eruptive styles, dynamics, and magma production rates on the seafloor. There has been no study that directly and quantitatively compares clast textures within raft and seafloor deposits sampled in situ through direct submersible operation from the same submarine eruption and/or eruptive vent
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
