Growth rates of lava domes with respect to viscosity of magmas

I. Yokoyama


In the discussion of lava dome formation, viscosity of magma plays an important role. Measurements of viscosity
of magmas in field and laboratory are briefly summarized. The types of lava dome emplacements are classified
into two, squeeze- and spine-type, by kinetic processes. The squeeze-type is the formation of a dome as a
result of squeezes of magma through conduits and the latter is solidified magma forced to ascend by underlying
fluid magma. An important parameter in the formation of such lava domes is their growth rates. Lava domes of
squeeze-type are governed by the Hagen-Poiseuille Law which involves their viscosoties and other eruption parameters.
At present, the real viscosity of magmas at the site of lava dome is still inaccessible. In order to avoid
uncertainty in viscosity of magmas, a conception of «macroscopic viscosity» is proposed, which involves effects
of chemical components, mainly SiO2 and volatile material, crystals and temperature, and their changes with
time. Lava dome formations during the 20th century are briefly examined and their growth rates are estimated.
The relationship between the growth rates and the SiO2 content of the magma is statistically studied, and the
macroscopic viscosity is empirically expressed as a function of SiO2 content. The linearity between the two parameters
is reasonably interpreted. This means that formation processes of lava domes are dominantly controlled
by macroscopic viscosity of magma.


lava domes;squeeze of magma;growth rates of domes;Hagen-Poiseuille Law;macroscopic viscosity

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Published by INGV, Istituto Nazionale di Geofisica e Vulcanologia - ISSN: 2037-416X