Contribution of fine ash to the atmosphere from plumes associated with pyroclastic density currents

A co-pyroclastic density current (co-PDC) plume forms as a mixture of fine-grained (<90 μm) particles and hot gas lofts from the top of a pyroclastic density current. Such plumes can rise tens of kilometers and inject substantial volumes of fine ash into the atmosphere with significant implications for airspace disruption, populations, livestock, and agriculture in downwind areas. Co-PDC deposits have a remarkably consistent grain size that remains constant with distance from source, regardless of eruption style, highlighting the complex sedimentation mechanisms that control deposition of co-PDC ash due to its fine grain size. Observations and numerical simulations of co-PDC onset emphasize the role played by the dynamics of PDCs in the development of co-PDC columns and plumes. The key differences between co-PDC and vent-derived plume source conditions and dispersion dynamics have important implications for application of remote sensing and numerical modeling methods

Resistance to experimental infections with Haemonchus contortus in Romanov sheep

International audienc

Performances de reproduction des brebis berrichonnes du cher, romanov et croisées. II. – Composantes de la prolificité

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Performances de reproduction des brebis berrichonnes du cher, romanov et croisées. I. – Activité sexuelle en début de saison et a contre saison

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Efficacy of once daily darunavir/ritonavir 800/100 mg in PI/r-experienced HIV-1 infected patients with suppressed HIV-1 replication: the RADAR study

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How do the grain size characteristics of a tephra deposit change over time?

Financial support was provided by the National Science Foundation of America through grant 1202692 ‘Comparative Island Ecodynamics in the North Atlantic’ and grant 1249313 ‘Tephra layers and early warning signals for critical transitions’ (both to AJD).Volcanologists frequently use grain size distributions (GSDs) in tephra layers to infer eruption parameters. However, for long-past eruptions, the accuracy of the reconstruction depends upon the correspondence between the initial tephra deposit and preserved tephra layer on which inferences are based. We ask: how closely does the GSD of a decades-old tephra layer resemble the deposit from which it originated? We addressed this question with a study of the tephra layer produced by the eruption of Mount St Helens, USA, in May 1980. We compared grain size distributions from the fresh, undisturbed tephra with grain size measurements from the surviving tephra layer. We found that the overall grain size characteristics of the tephra layer were similar to the original deposit, and that distinctive features identified by earlier authors had been preserved. However, detailed analysis of our samples showed qualitative differences, specifically a loss of fine material (which we attributed to ‘winnowing’). Understanding how tephra deposits are transformed over time is critical to efforts to reconstruct past eruptions, but inherently difficult to study. We propose long-term, tephra application experiments as a potential way forward.Publisher PDFPeer reviewe