caa a22 4500 475826310 CHVBK 20180406123829.0 cr unu---uuuuu 170329e20000801xx s 000 0 eng 10.1007/s004450000072 doi (NATIONALLICENCE)springer-10.1007/s004450000072 Melnik Oleg Institute of Mechanics, Moscow State University, 1-112-b, Mitchurinski pr., 119192, Moscow, Russia Fax: +7-095-939-01-65 e-mail: melnik@inmech.msu.su, RU aut Dynamics of two-phase conduit flow of high-viscosity gas-saturated magma: large variations of sustained explosive eruption intensity [Elektronische Daten] [Oleg Melnik]  The ascent of gas-saturated magma in a conduit can lead to the transition from the laminar flow of a bubble-rich melt to the turbulent flow of particle-rich hot gas in upper part of the conduit. This process is investigated with a help of a disequilibrium two-phase flow model for steady and unsteady conditions. For the description of different gas-magma flow regimes in the conduit separated sets of equations are used. The main difference from previous conduit flow models is the consideration of the pressure difference between a growing bubble and the surrounding melt. For a bubbly liquid to evolve into a gas-particle flow a critical overpressure value must be exceeded. This transition region is simulated by means of a discontinuity, namely by a fragmentation wave. The magma flow calculations are carried out for a given conduit length and overpressure between the magma chamber and the atmosphere. The steady solution of the boundary problem is not unique and there are up to five distinct steady regimes corresponding to fixed eruption conditions. Within the framework of the quasi-steady approach (governing parameters being varied monotonically) the transition from one regime to another can take place suddenly and is accompanied by the fundamental restructuring of the conduit flow, resulting in rapid or abrupt changes in the intensity of explosive eruptions. Abrupt intensification of an explosive eruption occurs when the chamber pressure becomes sufficiently less than saturation pressure, and therefore corresponds to the case of shallow-depth magma chamber and high initial water content. A regime with minimum flow rate may relate to the growth of a lava dome following the explosive phase of eruption. These models can explain geological observations that imply large and sudden changes of discharge rate in large-magnitude explosive eruptions, particularly at the transition between plinian phase and ignimbrite formation. Springer-Verlag Berlin Heidelberg, 2000 Key words Volcanic eruption nationallicence Conduit flow model nationallicence Magma chamber nationallicence Bubbly melt nationallicence Gas-particle dispersion nationallicence Fragmentation nationallicence Bubble overpressure nationallicence Discharge rate nationallicence https://doi.org/10.1007/s004450000072 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/s004450000072 text/html Onlinezugriff via DOI NATIONALLICENCE 100 1- Melnik Oleg Institute of Mechanics, Moscow State University, 1-112-b, Mitchurinski pr., 119192, Moscow, Russia Fax: +7-095-939-01-65 e-mail: melnik@inmech.msu.su, RU aut Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer