Havre 2012 pink pumice is evidence of a short-lived, deep-sea, magnetite nanolite-driven explosive eruption

Joseph Knafelc,Michael W M Jones,Guil Mallmann,David Gust,Eric C Ferré,Henrietta E Cathey,Daryl L Howard,Scott E Bryan,Andrew J Berry

doi:10.1038/s43247-022-00355-3

Abstract

The Havre 2012 deep-sea rhyolite eruption went unobserved and was initially recognised from a massive pumice raft at the sea surface. Havre pumices are predominantly white or grey, however pink pumice is common in the raft. In subaerial explosive eruptions, pink pumice is understood to result from high-temperature atmospheric iron-oxidation. The presence of pink pumice questions the effusive eruption model for the Havre raft. Here we report results from X-ray Absorption Near Edge Structure spectroscopy, magnetic measurements, TEM imaging and glass chemistry that collectively show the colour results from increasing amounts of magnetite nanolites in the raft pumice glass oxidizing to hematite. This suggests a short-lived but powerful explosive eruption phase penetrated the water column allowing hot pyroclasts to oxidise in air. Our results therefore challenge the known depth limits for explosive eruptions in the marine realm and suggest pink pumice can be an indicator of magnetite nanolite-driven explosive eruptions.

Highlights

The Havre 2012 deep-sea rhyolite eruption went unobserved and was initially recognised from a massive pumice raft at the sea surface
Due to the relatively short time pyroclasts are exposed to atmospheric oxygen conditions at high temperatures compared to oxygen diffusion rates in glass[11], we hypothesize that the pink colourisation is likely due to oxidation of magnetite microlites or nanolites to hematite
Magnetic analysis, backscattered electron (BSE) imaging, transmission electron microscopy (TEM) images and X-ray fluorescence microscopy (XFM) elemental maps indicate magnetite nanolites are pervasive in the Havre white raft pumice and are oxidized to hematite in the pink raft pumice

Summary

Introduction

The Havre 2012 deep-sea rhyolite eruption went unobserved and was initially recognised from a massive pumice raft at the sea surface. We show that the Havre pink pumice reflects hightemperature oxidation of magnetite nanolites and microlites and we interpret an explosive eruption column ejected pumice into the atmosphere at near magmatic temperatures (890 ± 27 °C41).

Results

Conclusion