Rheology of dacitic volcanoes: from magma chamber to eruptive style
Metadata[+] Show full item record
[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Arc and especially dacitic volcanoes present a large variety of eruptive styles, from effusive to explosive, that depends on the ability of the magma to degas. The rate of degassing is controlled by the viscosity of the melt, which strongly depends on the temperature and the composition, particularly the fraction of dissolved water. Measuring the viscosity of hydrous and anhydrous remelts in the range [approximate sign]10 to 1013 [pascal-second] between 663 and 1773 K, we show that the viscosity of hydrous arc magma on the calc-alkaline differentiation trend can be simplified to a function of temperature, silica and water contents. An empirical model for melt viscosity was developed that applies to the differentiation processes in the magma chamber, and to the liquid phase during its ascent in the conduit. Compaction experiments on natural rock samples reveal a temperature-dependent, non-Newtonian, shear-thinning, power-law rheology, with apparent viscosity reduced by the presence and deformation of vesicles. Applied to the volcanic activity of Santiaguito, Guatemala, the study supports current models of a magmatic slug pushed toward the surface like a piston, thanks to the shearing of the bubbles at the margin of the conduit. Moreover, it shows that lava has no yield strength, or lower than 5 [pascal-second]104 Pa at 890[degree sign]C, and therefore the dimensions of the flow are controlled by the temperature and the amount of material, i.e. thermodynamic properties and the effusion rate.
Access is limited to the campus of the University of Missouri-Columbia.