Simon J. Barker

Rapid priming, accumulation, and recharge of magma driving recent eruptions at a hyperactive caldera volcano

A major challenge in volcanology is determining the factors that control the frequency and magnitude of eruptions at hazardous caldera volcanoes. Understanding the critical sequence of events that may lead to future eruptions is vital for volcanic monitoring and risk assessment. Here we use magma chemistry and mineral diffusion modeling to interpret the magmatic processes and time scales involved in the youngest three eruptions (2.15–1.7 ka) from Taupo volcano (New Zealand), which peaked with the voluminous A.D. 232 eruption. Of the rhyolites erupted since ca. 12 ka, the 2.75 ka) rhyolites that were tapped from the same magma reservoir. Orthopyroxene Fe-Mg diffusion time scales indicate that the onset of rapid heating and priming of the host silicic mush occurred <120 yr prior to the <2.15 ka eruptions, with subsequent melt accumulation occurring in only decades. Elevated mafic magma supply to the silicic mush pile, rapid melt accumulation, and high differential tectonic stress built up and culminated in the ∼105 km3 A.D. 232 eruption, one of the largest and most violent Holocene eruptions globally. These youngest eruptions demonstrate how Taupo’s magmatic system can rapidly change behavior to generate large eruptible melt bodies on time scales of direct relevance to humans and monitoring initiatives.

Evolution of submarine eruptive activity during the 2011–2012 El Hierro event as documented by hydroacoustic images and remotely operated vehicle observations

Submarine volcanic eruptions are frequent and important events, yet they are rarely observed. Here we relate bathymetric and hydroacoustic images from the 2011 to 2012 El Hierro eruption with surface observations and deposits imaged and sampled by ROV. As a result of the shallow submarine eruption, a new volcano named Tagoro grew from 375 to 89 m depth. The eruption consisted of two main phases of edifice construction intercalated with collapse events. Hydroacoustic images show that the eruptions ranged from explosive to effusive with variable plume types and resulting deposits, even over short time intervals. At the base of the edifice, ROV observations show large accumulations of lava balloons changing in size and type downslope, coinciding with the area where floating lava balloon fallout was observed. Peaks in eruption intensity during explosive phases generated vigorous bubbling at the surface, extensive ash, vesicular lapilli and formed high-density currents, which together with periods of edifice gravitational collapse, produced extensive deep volcaniclastic aprons. Secondary cones developed in the last stages and show evidence for effusive activity with lava ponds and lava flows that cover deposits of stacked lava balloons. Chaotic masses of heterometric boulders around the summit of the principal cone are related to progressive sealing of the vent with decreasing or variable magma supply. Hornitos represent the final eruptive activity with hydrothermal alteration and bacterial mats at the summit. Our study documents the distinct evolution of a submarine volcano and highlights the range of deposit types that may form and be rapidly destroyed in such eruptions.

Comment on "Rapid cooling and cold storage in a silicic magma reservoir recorded in individual crystals"

Rubin et al. (Reports, 16 June 2017, p. 1154) proposed that gradients in lithium abundance in zircons from a rhyolitic eruption in New Zealand reflected short-lived residence at magmatic temperatures interleaved with long-term “cold” (<650°C) storage. Important issues arise with the interpretation of these lithium gradients and consequent crystal thermal histories that raise concerns about the validity of this conclusion.