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Marilena Filippucci
Ruolo
Ricercatore a tempo determinato - tipo A
Organizzazione
Università degli Studi di Bari Aldo Moro
Dipartimento
DIPARTIMENTO DI SCIENZE DELLA TERRA E GEOAMBIENTALI
Area Scientifica
AREA 04 - Scienze della Terra
Settore Scientifico Disciplinare
GEO/10 - Geofisica della Terra Solida
Settore ERC 1° livello
Non Disponibile
Settore ERC 2° livello
Non Disponibile
Settore ERC 3° livello
Non Disponibile
Recent laboratory studies on the rheology of lava samples from different volcanic areas have highlighted that the apparent viscosity depends on a power of the strain rate. Several authors agree in attributing this dependence to the crystal content of the sample and to temperature. Starting from these results, in this paper we studied the effect of a power law rheology on a gravity-driven lava flow. The equation of motion is nonlinear in the diffusion term, and an analytical solution does not seem to be possible. The finite volume method has been applied to solve numerically the equation governing the fully developed laminar flow of a power law non-Newtonian fluid in an inclined rectangular channel. The convergence, the stability, and the order of approximation were tested for the Newtonian rheology case, comparing the numerical solution with the available analytical solution. Results indicate that the assumption on the rheology, whether linear or nonlinear, strongly affects the velocity and/or the thickness of the lava channel both for channels with fixed geometry and for channels with constant flow rate. Results on channels with fixed geometry are confirmed by some simulations for real lava channels. Finally, the study of the Reynolds number indicates that gravity-driven lava channel flows are always in laminar regime, except for strongly nonlinear pseudoplastic fluids with low fluid consistency and at high slopes.
We studied the conditions of crust and tube formation of a lava flow moving under the effect of gravity in a rectangular cross-section channel and assumed a power-law rheology for lava. We followed the work of Valerio et al. (2008), who studied the effect of surface cooling on the formation and accretion of the crust in the central region of the channel, assuming for lava a Newtonian rheology. According to these authors, tube formation is influenced by topography and channel morphology. In this work, we extended this study to a non-Newtonian rheology, in particular to the power-law rheology. Results indicate that a power-law rheology strongly influences the condition of crust formation but does not produce significant differences as a function of topographical or morphological variations.
We present here the results from dynamical and thermal models that describe a channeled lava flow as it cools by radiation. In particular, the effects of power-law rheology and of the presence of bends in the flow are considered, as well as the formation of surface crust and lava tubes. On the basis of the thermal models, we analyze the assumptions implicit in the currently used formulae for evaluation of lava flow rates from satellite thermal imagery. Assuming a steady flow down an inclined rectangular channel, we solve numerically the equation of motion by the finite-volume method and a classical iterative solution. Our results show that the use of power-law rheology results in relevant differences in the average velocity and volume flow rate with respect to Newtonian rheology. Crust formation is strongly influenced by power-law rheology; in particular, the growth rate and the velocity profile inside the channel are strongly modified. In addition, channel curvature affects the flow dynamics and surface morphology. The size and shape of surface solid plates are controlled by competition between the shear stress and the crust yield strength: the degree of crust cover of the channel is studied as a function of the curvature. Simple formulae are currently used to relate the lava flow rate to the energy radiated by the lava flow as inferred from satellite thermal imagery. Such formulae are based on a specific model, and consequently, their validity is subject to the model assumptions. An analysis of these assumptions reveals that the current use of such formulae is not consistent with the model.
The cooling of a lava flow, both in the transient and the steady state, is investigated considering that lava rheology is pseudoplastic and dependent on temperature. Lava exits from the vent with constant velocity and flows down a slope under the effect of gravity force inside a channel of rectangular cross section. We consider that cooling of lava is caused by thermal radiation into the atmosphere and thermal conduction at the channel walls and at the ground. The heat equation is solved numerically in a 3D computational domain and the solution is tested to evaluate the numerical errors. We study the steady state and the initial transient period of lava cooling. Results indicate that the advective heat transport significantly modifies the cooling rate of lava slowing down the cooling process. Since the lava velocity depends on temperature, the cooling rate depends on the effusion temperature. Velocity profiles are modified during cooling showing two marginal static zones where the crust can form and remain stable. The fraction of crust coverage is calculated under the assumption that the solid lava is a plastic body with temperature dependent yield strength. We numerically confirm that heat advection can not be neglected in the mechanism of formation of lava tubes.
In this work we studied the effect of a power-law rheology on a gravity driven lava flow. Assuming a viscous fluid with constant temperature and constant density and assuming a steady flow in an inclined rectangular channel, the equation of the motion is solved by the finite volume method and a classical iterative solutor. Comparisons with observed channeled lava flows indicate that the assumption of the power-law rheology causes relevant differences in average velocity and volume flow rate with respect to the Newtonian rheology.
We investigated the cooling of a lava flow in the steady state considering that lava rheology is pseudoplastic and dependent on temperature. We consider that cooling of the lava is caused by thermal radiation at the surface into the atmosphere and thermal conduction at the channel walls and at the ground. The heat equation is solved numerically in a 3D computational domain. The fraction of crust coverage is calculated under the assumption that the solid lava is a plastic body with temperature dependent yield strength. We applied the results to the Mauna Loa (1984) lava flow. Results indicate that the advective heat transport significantly modifies the cooling rate of lava slowing down the cooling process also for gentle slope. Progress in Industrial Mathematics at ECMI 2012Progress in Industrial Mathematics at ECMI 2012 Look Inside Other actions Reprints and Permissions Export citation About this Book Add to Papers Share Share this content on Facebook Share this content on Twitter Share this content on LinkedIn
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