Abstract
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.
Highlights
Laboratory studies on basaltic melts show that lava rheology can show nonNewtonian behavior under certain conditions, which include vesicularity [Spera et al 1988, Stein and Spera 1992, Badgassarov and Pinkerton 2004], crystal concentration [Pinkerton and Stevenson 1992, Smith 2000, Sonder et al 2006, Champallier et al 2008], and temperature and shear rates [Shaw et al 1968]
The literature indicates that magmas have nonNewtonian, pseudoplastic behavior, with the exception of Smith [2000], who attributes a dilatant rheology to lava at high crystal concentrations
We explored how variations in the channel width, ground slope and volume flow rate can affect the formation of a lava tube, assuming a power-law rheology
Summary
Laboratory studies on basaltic melts show that lava rheology can show nonNewtonian behavior under certain conditions, which include vesicularity [Spera et al 1988, Stein and Spera 1992, Badgassarov and Pinkerton 2004], crystal concentration [Pinkerton and Stevenson 1992, Smith 2000, Sonder et al 2006, Champallier et al 2008], and temperature and shear rates [Shaw et al 1968]. We consider the effects of the curvature of a channel on the lava velocity and shear stress, and on the formation of the solid crust at the flow surface. We evaluated the effects of the nonlinearity of the lava rheology on crust formation, by modeling the plastic behavior of the crust using a temperature-dependent yield strength x, given by: x
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