Direct observation of degassing during decompression of basaltic magma.

Transitions in eruptive style during volcanic eruptions strongly depend on how easily gas and magma decouple during ascent. Stronger gas-melt coupling favors highly explosive eruptions, whereas weaker coupling promotes lava fountaining and lava flows. The mechanisms producing these transitions are still poorly understood because of a lack of direct observations of bubble dynamics under natural magmatic conditions. Here, we combine x-ray radiography with a novel high-pressure/high-temperature apparatus to observe and quantify in real-time bubble growth and coalescence in basaltic magmas from 100 megapascals to surface. For low-viscosity magmas, bubbles coalesce and recover a spherical shape within 3 seconds, implying that, for lava fountaining activity, gas and melt remain coupled during the ascent up to the last hundred meters of the conduit. For higher-viscosity magmas, recovery times become longer, promoting connected bubble pathways. This apparatus opens frontiers in unraveling magmatic/volcanic processes, leading to improved hazard assessment and risk mitigation.

Dendritic crystallization in hydrous basaltic magmas controls magma mobility within the Earth's crust.

The majority of basaltic magmas stall in the Earth's crust as a result of the rheological evolution caused by crystallization during transport. However, the relationships between crystallinity, rheology and eruptibility remain uncertain because it is difficult to observe dynamic magma crystallization in real time. Here, we present in-situ 4D data for crystal growth kinetics and the textural evolution of pyroxene during crystallization of trachybasaltic magmas in high-temperature experiments under water-saturated conditions at crustal pressures. We observe dendritic growth of pyroxene on initially euhedral cores, and a surprisingly rapid increase in crystal fraction and aspect ratio at undercooling ≥30 °C. Rapid dendritic crystallization favours a rheological transition from Newtonian to non-Newtonian behaviour within minutes. We use a numerical model to quantify the impact of rapid dendritic crystallization on basaltic dike propagation, and demonstrate its dramatic effect on magma mobility and eruptibility. Our results provide insights into the processes that control whether intrusions lead to eruption or not.

In situ observation of nanolite growth in volcanic melt: A driving force for explosive eruptions.

Although gas exsolution is a major driving force behind explosive volcanic eruptions, viscosity is critical in controlling the escape of bubbles and switching between explosive and effusive behavior. Temperature and composition control melt viscosity, but crystallization above a critical volume (>30 volume %) can lock up the magma, triggering an explosion. Here, we present an alternative to this well-established paradigm by showing how an unexpectedly small volume of nano-sized crystals can cause a disproportionate increase in magma viscosity. Our in situ observations on a basaltic melt, rheological measurements in an analog system, and modeling demonstrate how just a few volume % of nanolites results in a marked increase in viscosity above the critical value needed for explosive fragmentation, even for a low-viscosity melt. Images of nanolites from low-viscosity explosive eruptions and an experimentally produced basaltic pumice show syn-eruptive growth, possibly nucleating a high bubble number density.

Nanoscale uniform self-assembled monolayers of fluorescent zinc(II) complexes on the Si(100) surface.

The synthesis of self-assembled monolayers on Si(100) substrates of a new fluorescent Zn(II) Schiff-base complex is reported. Chemisorbed species are characterized by the combination of fluorescence scanning near-field optical/atomic force microscopy (SNOM/AFM), and by fluorescence spectroscopy. Both SNOM/AFM results indicate the existence of a monolayer on the surface, while optical SNOM images highlight the contribution of the monolayer to the local fluorescence. While chemisorbed molecular monolayers exhibit a distinct fluorescence, analogous to that observed in solution, cast thin films do not show any emission. Photoluminescent properties of the monolayer can be related to its nanoscale uniform, ordered structure.

Engineering coordination assemblies of dinuclear CuII complexes.

Hybrid organic-inorganic coordination assemblies are synthesized using modified aminocarboxylic acid ligands as the structure-directing agents. The synthetic approach results in two novel dinuclear copper(II) complexes, K2[CuII(hnida)]2.2H2O (1) and K4[CuII(chnida)]2.4H2O.4MeOH (2) that assemble in the presence of suitable counterions into a densely packed hexagonal array or an open-framework structure. The functionality of the aminocarboxylic acid ligands provides a tool to control the supramolecular structure. The materials combine promising thermal stabilities with the necessary flexibility to withstand structural changes induced by calcinations or the uptake and release of guest molecules. The structural and physicochemical properties of the complexes were investigated using X-ray diffraction, magnetic measurements, thermogravimetric analysis and spectroscopy.