Search

Explosive eruptions at basaltic volcanoes have been linked to gas segregation from magmas at shallow depths in the crust. The composition of primary melts formed at greater depths was thought to have little influence on eruptive style. Ocean island basaltic volcanoes are the product of melting of a geochemically heterogeneous mantle plume and are expected to give rise to heterogeneous primary melts. This range in primary melt composition, particularly with respect to the volatile components, will profoundly influence magma buoyancy, storage and eruption style. Here we analyse the geochemistry of a suite of melt inclusions from 25 historical eruptions at the ocean island volcano of Kīlauea, Hawai'i, over the past 600 years. We find that more explosive styles of eruption at Kīlauea Volcano are associated statistically with more geochemically enriched primary melts that have higher volatile concentrations. These enriched melts ascend faster and retain their primary nature, undergoing little interaction with the magma reservoir at the volcano's summit. We conclude that the eruption style and magma-supply rate at Kīlauea are fundamentally linked to the geochemistry of the primary melts formed deep below the volcano. Magmas might therefore be predisposed towards explosivity right at the point of formation in their mantle source region. [ABSTRACT FROM AUTHOR]

Abstract: The 2008–current summit eruption at Kīlauea Volcano, Hawai‘i offers a unique opportunity to test models of degassing and magma plumbing and to improve our understanding of the volatile budget. The aim of this work was to test the hypothesis that gases emitted from a summit lava lake will be rich in carbon dioxide (CO2) and similar to those measured during the persistent lava lake activity in the early 20th century at Kīlauea Volcano (Gerlach and Graeber, 1985). We measured the sulfur dioxide (SO2) and CO2 concentrations in the gas plume from Halema‘uma‘u using electrochemical and non-dispersive infrared sensors during April 2009. We also analysed olivine-hosted melt inclusions from tephra erupted in 2008 and 2010 for major, trace and volatile elements. The gas and melt data are both consistent with the equilibration of a relatively evolved magma batch at depths of 1.2–2.0km beneath Halema‘uma‘u prior to the current degassing activity. The differences in the volatile concentrations between the melt inclusions and matrix glasses are consistent with the observed gas composition. The degassing of sulfur and halogen gases from the melt requires low pressures and hence we invoke convection to bring the magma close to the surface to degas, before sinking back into the conduit. The fluxes of gases (900 and 80t/d SO2 and CO2 respectively) are used to estimate magma fluxes (1.2–3.4m3/s) to the surface for April 2009. The observation of minimal loss of hydrogen from the melt inclusions implies a rapid rise rate (less than a few hours), which constrains the conduit radius to 1–2m. The inferred conduit radius is much narrower than the lava lake at the surface, implying a flared geometry. The melt inclusion data suggest that there is a progressive decrease in melt volatile concentrations with time during 2008–2010, consistent with convection, degassing and mixing in a closed, or semi-closed magma system. The degassing regime of the current summit lava lake activity is not similar to that observed in the early 20th century; instead the gases are extensively depleted in CO2. [Copyright &y& Elsevier]

The weakest explosive volcanic eruptions globally, Strombolian explosions and Hawaiian fountaining, are also the most common. Yet, despite over a hundred years of observations, no classifications have offered a convincing, quantitative way of demarcating these two styles. New observations show that the two styles are distinct in their eruptive time scale, with the duration of Hawaiian fountaining exceeding Strombolian explosions by ~300-10,000 s. This reflects the underlying process of whether shallow-exsolved gas remains trapped in the erupting magma or is decoupled from it. We propose here a classification scheme based on the duration of events (brief explosions versus prolonged fountains) with a cutoff at 300 s that separates transient Strombolian explosions from sustained Hawaiian fountains. [ABSTRACT FROM AUTHOR]