Basement sliding and the formation of fault systems on Mt Etna volcano

The influence of faulting on the eruptive mechanisms of Mt Etna has been intensively studied, especially regarding the importance of regional tectonics, magma pressure, gravitational spreading and east flank instability. Here we examine the influence of an additional process: the wholesale sliding of the Etna massif along its sloping basement. Using laboratory analogue experiments, we create a series of model volcanoes on sloping basements, with obstructions to represent the mountains and hills surrounding Etna, and an unconstrained downslope edge to represent the unbuttressed seaward slopes. We find that analogues of all the Etna fault systems can be produced in the same model. Furthermore, we find that the relative velocities of transcurrent faulting and extension of each model flank fault system match those of Mt Etna in every case. We also find convincing evidence that gravitational spreading of the summit cone, combined with downslope sliding, controls the position of future eruptive vents around the summit, by creating faults and fractures that form paths of least resistance for magma intrusions. The intruding magma in turn augments fracture opening by an order of magnitude, in a feedback process that dominates within the summit graben. We conclude that gravitational spreading and sliding are the dominant processes in creating faults at Etna, and that these two processes, augmented by magma pressure, are responsible for the rapid seaward movement of the eastern slopes, tectonically cut off from the stable western flanks. The influence of regional tectonism is up to two orders of magnitude lower. The conceptual model derived here could make an important contribution to the investigation and monitoring of eruptive, seismic and landslide hazards, by providing a unified mechanical system that can be used to understand deformation.

A Database of Laboratory Analogue Models of Caldera Collapse Testing the Role of Inherited Structures

Since caldera collapse deformation is extremely difficult to study in real time - due to the high deformation rates that characterize this process and the difficult access to the caldera structures-analogue modeling has been widely used during past decades to integrate field data and, more recently, remote-sensing data (e.g., InSAR). However, the relationships between caldera collapse and inherited discontinuities, such as inherited crustal faults, remain poorly investigated. We therefore provide a new dataset of analogue models that aims to specifically address this issue and that can be potentially compared with literature and natural case studies worldwide. We present a dataset of 13 analogue models of caldera collapse investigating the interactions between caldera collapse processes and inherited crustal discontinuities. The dataset is composed of raw data and elaborations that can be used to qualitatively visualize and/or quantitatively analyze model deformation through the use of top-view photos, digital elevation models (DEM) and digital particle image velocimetry (DPIV).

Compositional heterogeneity amongst salt-rich grains emitted from Enceladus’ subsurface ocean

<p>Salt-rich icy particles within Saturn’s E-Ring are relatively young (<~200 years), and originate from frozen aerosolized droplets of the salty seawater of Enceladus’ subsurface ocean, ejected into space, through fractures in the moon’s south polar region, within a plume of gas and ice particles. The salt-rich grains are therefore believed to reflect the composition of the ocean water. In situ mass spectra of the plume and E-ring icy particles, obtained by the Cosmic Dust Analyzer (CDA) impact ionization mass spectrometer onboard the Cassini spacecraft, indicate significant compositional diversity within the salt-rich population. Understanding the compositions of dissolved salts within the grains, and thus the ocean, can provide important constraints for geochemical models of Enceladus’ core/ocean environment.</p><p>To investigate and quantify variations in grain composition, a Laser Induced Liquid Beam Ion Desorption (LILBID) technique has been used to desorb and ionize a wide range of Enceladean ocean-like solutions containing dissolved salts. The resulting ions were then measured by a reflectron-type time of flight mass spectrometer. As the laser desorption mechanism simulates the ice grain impact process occurring on the CDA target, spectra produced in the laboratory from a large range of well-characterized salt solutions can be used to determine the CDA-applicable spectral appearances of substances within the ice grains emitted from Enceladus’ ocean.</p><p>Here we present the results of an investigation of CDA E-ring spectra, supported by laboratory analogue experiments, which show significant compositional heterogeneity within the salt-rich grains originating from Enceladus’ subsurface ocean. Two main spectral subtypes, representing endmember compositions within the salt-rich grains, are identified. These mass spectra are dominated by features from chloride-rich or carbonate-rich compounds and the laboratory detectability of other, additional, compounds within these brines is discussed.</p>

Generation of photoionized plasmas in the laboratory: Analogues to astrophysical sources

Implementation of a novel experimental approach using a bright source of narrowband x-ray emission has enabled the production of a photoionized argon plasma of relevance to astrophysical modelling codes such as Cloudy. We present results showing that the photoionization parameter ζ = 4πF/ne generated using the VULCAN laser was ≈ 50 erg cm s−1, higher than those obtained previously with more powerful facilities. Comparison of our argon emission-line spectra in the 4.15 - 4.25 Å range at varying initial gas pressures with predictions from the Cloudy code and a simple time-dependent code are also presented. Finally we briefly discuss how this proof-of-principle experiment may be scaled to larger facilities such as ORION to produce the closest laboratory analogue to a photoionized plasma.