Andrea Tallarico

Temperature distribution inside and around a lava tube

Abstract We propose a model describing the thermal effects of a lava tube. The tube is a circular cylinder, embedded in a solid medium and filled with a Newtonian liquid flowing under the gravity force. Steady-state conditions are considered. The velocity field in the tube, evaluated by the Navier–Stokes equation, is introduced into the heat equation taking into account the viscous dissipation. The temperature distribution is evaluated both inside the tube and in the surrounding solid medium. Under the assumption that the lava tube is embedded in a solid half-space, the surface heat flow due to the presence of the tube is calculated. It is shown that heat flow measurements at the Earth’s surface can give information on the depth, size and temperature of the buried lava tube.

Modeling of the steady-state temperature field in lava flow levées

The rationale of lava flow deviation is to prevent major damage, and, among the possible techniques, the opening of the flow levees has often been demonstrated to be suitable and reliable. The best way to open the levees in the right point, in order to obtain the required effect, is to produce an explosion in situ, and it is then necessary to map with the highest precision the temperature field inside the levees, in order to design a safe and successful intervention. The levees are formed by lava flows due to their non-Newtonian rheology, where the shear stress is lower than the yield stress. The levees then cool and solidify due to heat loss into the atmosphere. In this work we present analytical solutions of the steady-state heat conduction problem in a levee using the method of conformal mapping for simple geometrical shapes of the levee cross-section (triangular or square). Numerical solutions are obtained with a finite-element code for more complex, realistic geometries.

Interaction between shallow and subcrustal dislocations on a normal fault

Abstract We propose a model which may explain seismic sequences which are often observed in seismogenic regions, as for example in the Apenninic chain (Italy). In particular, we consider a normal fault and earthquakes taking place at different depths: a first shock in a shallower layer and a second in a deeper one. The normal fault is embedded in a viscoelastic half-space. As a consequence of the rheology, there are two different brittle layers, a shallower and a deeper one, where earthquakes can nucleate. Between these two layers, the rheological behavior is ductile. The thicknesses of the layers depend on the geothermal profile that is calculated taking into account the profile of the thermal and rheological parameters with depth. The fault plane, crossing layers with different rheological behavior, is heterogeneous in respect to the slip style: seismic in the brittle layers, aseismic in the ductile layer. Dislocations in the shallower layer are assumed to produce aseismic slip in the area of the fault belonging to the ductile layer. The stress concentrated, by the seismic and aseismic dislocations, on the fault plane section in the deeper brittle layer is evaluated. It is compared with the tectonic stress rate in order to calculate how much earlier the second earthquake would occur compared to if just the bare tectonic sstress was acting. It results that such an advance is comparable with typical recurrence times of earthquakes and so a mechanism of interaction between different seismic sources, mediated by aseismic slip, can be supposed. The strains and displacements at the Earth’s surface due to seismic and aseismic slip are calculated. They are large enough to be detected by present geodetic techniques.

Thermal and Rheological Aspects in a Channeled Lava Flow

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.