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Antonio Costa

Publications and source records attributed to Antonio Costa.

4 recordsLinked to original sources

Eruption column modelling of explosive volcanism on Venus

Volcanism on Venus has never been directly observed, but several measurements indicate present-day activity. Volcanism could potentially play a role in climatic processes on Venus, especially in the sulfur cycle like on Earth. Observation of volcanic activity is the primary objective of future Venus spacecraft. However, there are many unknowns regarding its Venusian characteristics, like the condition at the vent, the volatile content and composition. Past modelling efforts have only studied explosive volcanic plume propagation over a limited range of flow parameters at the vent and in an idealised Venus atmospheric configuration. We propose to use the 1D FPLUME volcanic plume model in a realistic Venusian environment. In similar Venusian conditions, the height of the plume is consistent with past modelling. The present study shows that explosive volcanism would preferably reach 15 km of altitude. Under certain conditions, plumes are able to reach the VenSpec-H tropospheric altitude range of observations and even the 45 km cloud floor. For the first time, the impact of wind was quantified, and the super-rotating winds have a substantial impact by plume-bending of reducing the height of plumes. Contrary to the Earth, the atmospheric heat capacity depends greatly on temperature, and will disadvantage lower plumes and allow larger plumes to propagate at higher altitudes. The high latitude atmospheric environment, due to the thermal profile and weaker winds, is favorable to plumes reaching higher altitudes.

astro-ph.EP

On isolated strata of p-gonal Riemann surfaces in the branch locus of moduli spaces

The moduli space $\mathcal{M}_{g}$ of compact Riemann surfaces of genus $g$ has orbifold structure, and the set of singular points of such orbifold is the \textit{branch locus} $\mathcal{B}_{g}$. Given a prime number $p \ge 7$, $\mathcal{B}_{g}$ contains isolated strata consisting of $p$-gonal Riemann surfaces for genera $g \ge {3(p-1)\over 2}$,that are multiple of ${p-1 \over 2}$. This is a generalization of the results obtained in \cite{[BCI1]} for pentagonal Riemann surfaces, and the results of \cite{[K]} and \cite{[CI3]} for zero- and one-dimensional isolated strata in the branch locus.

math.GT

Numerical simulation of lava flows based on depth-averaged equations

Risks and damages associated with lava flows propagation (for instance the most recent Etna eruptions) require a quantitative description of this phenomenon and a reliable forecasting of lava flow paths. Due to the high complexity of these processes, numerical solution of the complete conservation equations for real lava flows is often practically impossible. To overcome the computational difficulties, simplified models are usually adopted, including 1-D models and cellular automata. In this work we propose a simplified 2D model based on the conservation equations for lava thickness and depth-averaged velocities and temperature which result in first order partial differential equations. The proposed approach represents a good compromise between the full 3-D description and the need to decrease the computational time. The method was satisfactorily applied to reproduce some analytical solutions and to simulate a real lava flow event occurred during the 1991-93 Etna eruption.

physics.geo-ph

Nonlinear phenomena in fluids with temperature-dependent viscosity: an hysteresis model for magma flow in conduits

Magma viscosity is strongly temperature-dependent. When hot magma flows in a conduit, heat is lost through the walls and the temperature decreases along the flow causing a viscosity increase. For particular values of the controlling parameters the steady-flow regime in a conduit shows two stable solutions belonging either to the slow or to the fast branch. As a consequence, this system may show an hysteresis effect, and the transition between the two branches can occur quickly when certain critical points are reached. In this paper we describe a model to study the relation between the pressure at the inlet and the volumetric magma flow rate in a conduit. We apply this model to explain an hysteric jump observed during the dome growth at Soufrière Hills volcano (Montserrat), and described by Melnik and Sparks [1999] using a different model.

physics.geo-ph