It is unclear what role the experimental drug and convalescent plasma had in the recovery of these patients. Prospective clinical trials are needed to delineate the role of investigational therapies in the care of patients with EVD.

The mechanisms of hazardous silicic eruptions are controlled by complex, poorly-understood conduit processes. Observations of recent Chilean rhyolite eruptions have revealed the importance of hybrid activity, involving simultaneous explosive and effusive emissions from a common vent. Such behavior hinges upon the ability of gas to decouple from magma in the shallow conduit. Tuffisite veins are increasingly suspected to be a key facilitator of outgassing, as they repeatedly provide a transient permeable escape route for volcanic gases. Intersection of foam domains by tuffisite veins appears critical to efficient outgassing. However, knowledge is currently lacking into textural heterogeneities within shallow conduits, their relationship with tuffisite vein propagation, and the implications for fragmentation and degassing processes. Similarly, the magmatic vesiculation response to upper conduit pressure perturbations, such as those related to the slip of dense magma plugs, remains largely undefined. Here we provide a detailed characterization of an exceptionally large tuffisite vein within a rhyolitic obsidian bomb ejected during transitional explosive-effusive activity at Chaitén, Chile in May 2008. Vein textures and chemistry provide a time-integrated record of the invasion of a dense upper conduit plug by deeper fragmented magma. Quantitative textural analysis reveals diverse vesiculation histories of various juvenile clast types. Using vesicle size distributions, bubble number densities, zones of diffusive water depletion, and glass H 2 O concentrations, we propose a multi-step degassing/fragmentation history, spanning deep degassing to explosive bomb ejection. Rapid decompression events of ∼3-4 MPa are associated with fragmentation of foam and dense magma at ∼200-360 m depth in the conduit, permitting vertical gas and pyroclast mobility over hundreds of meters. Permeable pathway occlusion in the dense conduit plug by pyroclast accumulation and sintering preceded ultimate bomb ejection, which then triggered a final bubble nucleation event. Our results highlight how the vesiculation response of magma to decompression events is highly sensitive to the local melt volatile concentration, which is strongly spatially Saubin et al.Chaitén Tuffisites Record Conduit Processes heterogeneous. Repeated opening of pervasive tuffisite vein networks promotes this heterogeneity, allowing juxtaposition of variably volatile-rich magma fragments that are derived from a wide range of depths in the conduit. This process enables efficient but explosive removal of gas from rhyolitic magma and creates a complex textural collage within dense rhyolitic lava, in which neighboring fused clasts may have experienced vastly different degassing histories.

The degassing of magmatic volatiles during eruptions beneath ice sheets and glaciers, as recorded by the dissolved volatile content quenched in volcanic rocks, could provide powerful new constraints on former ice thicknesses in volcanic areas. As volcanic rocks are readily dateable using radiometric methods, subglacial volcanoes may therefore provide crucial information on the timing of palaeo-environmental fluctuations in the Quaternary. Volatile degassing is also likely to control the mechanisms of subglacial eruptions and their associated hazards. In this paper we lay out a number of criteria that must be satisfied for degassing to potentially record palaeo-ice thicknesses, using a variety of new datasets and calculations to highlight existing problems with the technique. These include uncertainties about volatile solubilities, non-equilibrium degassing, sample heterogeneity, hydration, post-quenching movement and whether subglacial pressures deviated significantly from glaciostatic. We propose new strategies for improvement of the technique and discuss how magmatic volatiles may control the style of subglacial eruptions.

Rhyolitic eruptions beneath Icelandic glaciers can be highly explosive, as demonstrated by Quaternary tephra layers dispersed throughout northern Europe. However, they can also be small and effusive. A subglacial rhyolitic eruption has never been observed, so behavioral controls remain poorly understood and the influence of preeruptive volatile contents is unknown. We have therefore used secondary ion mass spectrometry to characterize pre-eruptive volatile contents and degassing paths for five subglacial rhyolitic edifices within the Torfajökull central volcano, formed in contrasting styles of eruption under ice ~400 m thick. This includes the products of the largest known eruption of Icelandic subglacial rhyolite of ~16 km 3 at ca. 70 ka. We find pre-eruptive water contents in melt inclusions (H 2 O MI ) of up to 4.8 wt%, which indicates that Icelandic rhyolite can be significantly more volatile rich than previously thought. Our results indicate that explosive subglacial rhyolite eruptions correspond with high H 2 O MI , closed-system degassing, and rapid magma ascent, whereas their effusive equivalents have lower H 2 O MI and show open-system degassing and more sluggish ascent rates.

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