The role of magma composition and water content in explosive eruptions: 1. Conduit ascent dynamics

Abstract The role of anhydrous magma composition, water content, and crystal content on the dynamics of explosive eruptions is investigated by modeling the ascent of magma along volcanic conduits and the subsequent pyroclastic dispersion in the atmosphere, described in a companion paper [Neri, A., Papale, P., Macedonio, G., 1998. The role of magma composition and water content in explosive eruptions: 2. Pyroclastic dispersion dynamics. J. Volcanol. Geotherm. Res., 87, 95–115.]. The conduit model used is based on the solution of the fundamental transport equations assuming steady-state and isothermal flow conditions, and includes a composition-based description of magma properties and their variations along the conduit. This study stems from the well-documented vertical compositional variation of many pyroclastic deposits, often associated with reconstructed variations in initial water content. The results of the modeling show complex and sometimes non-intuitive dependence of the distribution of the flow variables on magma composition, crystal and water contents. In general, a water content decrease is expected to produce a decrease in mass flow-rate, decrease in pressure and velocity along the conduit, an increase in the exit gas volume fraction, and a decrease in velocity, pressure, and mixture density at the conduit exit. Reverse variations are expected to occur by decreasing the degree of chemical evolution of the liquid at a constant water content, apart from exit velocities which show more complex variations. The overall effect of increasing crystals is in general similar to that of increasing the degree of chemical evolution of the liquid, or decreasing the water content. The above results are to a large extent interpreted in terms of variations in magma viscosity, which is recognized as the critical magma property besides water content in the dynamics of magma ascent. The common compositional trend of explosive eruptions characterized by chemically evolved, water-richer and crystal-poorer magma erupted first is predicted to be associated with variations in the evolution of the eruption dynamics, depending on the relative magnitude of the changes. However, the exit velocity always decreases in the above trend, and the mass flow-rate increases in most relevant cases, comparing well with the results of chemical and stratigraphic studies of the deposits from explosive eruptions.

[1]  A. Freundt,et al.  Mixing of rhyolite, trachyte and basalt magma erupted from a vertically and laterally zoned reservoir, composite flow P1, Gran Canaria , 1992 .

[2]  C. Mandeville,et al.  Magma mixing, fractional crystallization and volatile degassing during the 1883 eruption of Krakatau volcano, Indonesia , 1996 .

[3]  W. Hildreth,et al.  The plinian eruptions of 1912 at Novarupta, Katmai National Park, Alaska , 1992 .

[4]  J. Ritchey.  Divergent magmas at Crater Lake, Oregon: Products of fractional crystallization and vertical zoning in a shallow, water-undersaturated chamber , 1980 .

[5]  R. Cioni,et al.  Compositional Layering and Syn-eruptive Mixing of a Periodically Refilled Shallow Magma Chamber: the AD 79 Plinian Eruption of Vesuvius , 1995 .

[6]  Bradford Sturtevant,et al.  Laboratory studies of volcanic jets , 1984 .

[7]  P. Papale,et al.  Magma flow along the volcanic conduit during the Plinian and pyroclastic flow phases of the May 18, 1980, Mount St. Helens eruption , 1994 .

[8]  F. Spera.  Some Numerical Experiments on the Withdrawal of Magma from Crustal Reservoirs , 1984 .

[9]  R. Santacroce,et al.  Magma mixing and convective compositional layering within the Vesuvius magma chamber , 1991 .

[10]  C. Bacon.  Eruptive history of Mount Mazama and Crater Lake Caldera, Cascade Range, U.S.A. , 1983 .

[11]  A. Freundt,et al.  Petrogenesis of rhyolite‐trachyte‐basalt composite ignimbrite P1, Gran Canada, Canary Islands , 1995 .

[12]  Grant Heiken,et al.  Geochemical zoning, mingling, eruptive dynamics and depositional processes — the Campanian Ignimbrite, Campi Flegrei caldera, Italy , 1997 .

[13]  G. Valentine,et al.  Entrainment of Country Rock during Basaltic Eruptions of the Lucero Volcanic Field, New Mexico , 1996, The Journal of Geology.

[14]  G. Ivey,et al.  Density and viscosity gradients in zoned magma chambers, and their influence withdrawal dynamics , 1986 .

[15]  H. Sigurdsson,et al.  Temporal variations in column height and magma discharge rate during the 79 A.D. eruption of Vesuvius , 1987 .

[16]  Augusto Neri,et al.  Influence of eruption parameters on the thermofluid dynamics of collapsing volcanic columns , 1994 .

[17]  One‐dimensional, time‐dependent, homogeneous, two‐phase flow in volcanic conduits , 1995 .

[18]  A. Neri,et al.  Erosion processes in volcanic conduits and application to the AD 79 eruption of Vesuvius , 1994 .

[19]  C. W. Criswell,et al.  Chronology and pyroclastic stratigraphy of the May 18, 1980, eruption of Mount St. Helens, Washington , 1987 .

[20]  N. Zuber,et al.  Drag coefficient and relative velocity in bubbly, droplet or particulate flows , 1979 .

[21]  G. Walker.  Explosive volcanic eruptions — a new classification scheme , 1973 .

[22]  Lionel Wilson,et al.  Ascent and eruption of basaltic magma on the earth and moon , 1981 .

[23]  Highlights of two-phase critical flow: On the links between maximum flow rates, sonic velocities, propagation and transfer phenomena in single and two-phase flows , 1976 .

[24]  R. Lange,et al.  Densities of Na2O-K2O-CaO-MgO-FeO-Fe2O3-Al2O3-TiO2-SiO2 liquids: New measurements and derived partial molar properties , 1987 .

[25]  D. Turcotte,et al.  A mathematical model of vulcanian eruptions , 1990 .

[26]  Andrew W. Woods,et al.  The decompression of volcanic jets in a crater during explosive volcanic eruptions , 1995 .

[27]  D. Yuen,et al.  Simulations of magma withdrawal from compositionally zoned bodies , 1992 .

[28]  A. Bertagnini,et al.  The Pomici di Base plinian eruption of Somma-Vesuvius , 1998 .

[29]  D. Yuen,et al.  Dynamics of magma withdrawal from stratified magma chambers. , 1986 .

[30]  P. Papale,et al.  Modeling of the ascent of magma during the plinian eruption of Vesuvius in A.D. 79 , 1993 .

[31]  H. R. Shaw.  Viscosities of magmatic silicate liquids; an empirical method of prediction , 1972 .

[32]  Susan Werner Kieffer,et al.  Sound Speed in Liquid-Gas Mixtures' Water-Air and Water-Steam , 1977 .

[33]  R. Scandone.  Factors controlling the temporal evolution of explosive eruptions , 1996 .

[34]  G. Walker.  Downsag calderas, ring faults, caldera sizes, and incremental caldera growth , 1984 .

[35]  Hans-Ulrich Schmincke,et al.  Petrogenesis of the Zoned Laacher See Tephra , 1984 .

[36]  P. Lipman.  Mineral and chemical variations within an ash-flow sheet from Aso caldera, Southwestern Japan , 1967 .

[37]  K. Cashman,et al.  Permeability development in vesiculating magmas: implications for fragmentation , 1996 .

[38]  S. Morse.  Magmatic processes: Physicochemical principles: Edited by B. O. Mysen. The Geochemical Society, spec. pub. no. 1, 1987, 500p., $45.00 (Geochemical Society Members), $65.00 (other). (ISBN 0-941809-005) , 1988 .

[39]  P. Papale.  Modeling of the solubility of a one-component H2O or CO2 fluid in silicate liquids , 1997 .

[40]  Augusto Neri,et al.  NUMERICAL SIMULATION OF COLLAPSING VOLCANIC COLUMNS , 1993 .

[41]  C. Jaupart,et al.  Gas content, eruption rate and instabilities of eruption regime in silicic volcanoes , 1991 .

[42]  M. Rosi,et al.  The 1631 Vesuvius eruption. A reconstruction based on historical and stratigraphical data , 1993 .

[43]  Lionel Wilson,et al.  Explosive volcanic eruptions — IV. The control of magma properties and conduit geometry on eruption column behaviour , 1980 .

[44]  S. Self,et al.  The October 1902 plinian eruption of Santa Maria volcano, Guatemala , 1983 .

[45]  A. Woods,et al.  Control of magma volatile content and chamber depth on the mass erupted during explosive volcanic eruptions , 1997 .

[46]  G. Buresti,et al.  One-dimensional adiabatic flow of equilibrium gas–particle mixtures in long vertical ducts with friction , 1989, Journal of Fluid Mechanics.

[47]  H. Sigurdsson,et al.  The intensity of plinian eruptions , 1989 .

[48]  G. Wallis.  One Dimensional Two-Phase Flow , 1969 .

[49]  G. Ivey,et al.  Magma-mixing and the dynamics of withdrawal from stratified reservoirs , 1986 .

[50]  Paolo Papale,et al.  The role of magma composition and water content in explosive eruptions: 2. Pyroclastic dispersion dynamics , 1998 .

[51]  L. Wilson,et al.  Explosive volcanic eruptions - VI. Ejecta dispersal in plinian eruptions: the control of eruption conditions and atmospheric properties , 1987 .

[52]  S. Vergniolle,et al.  Separated two‐phase flow and basaltic eruptions , 1986 .

[53]  R. A. Bailey,et al.  The Bandelier Tuff: A study of ash-flow eruption cycles from zoned Magma Chambers , 1966 .

[54]  F. Dobran.  Nonequilibrium flow in volcanic conduits and application to the eruptions of Mt. St. Helens on May 18, 1980, and Vesuvius in AD 79 , 1992 .

[55]  L. Lirer,et al.  Two Plinian Pumice-Fall Deposits from Somma-Vesuvius, Italy , 1973 .

[56]  R. Sparks,et al.  The dynamics of bubble formation and growth in magmas , 1978 .

[57]  H. Sigurdsson,et al.  Eruption dynamics and magma withdrawal during the Plinian Phase of the Bishop Tuff Eruption, Long Valley Caldera , 1991 .

[58]  R. K. Duggins,et al.  Speed of Sound in Bubbly Liquids , 1969 .

[59]  B. Marsh.  On the crystallinity, probability of occurrence, and rheology of lava and magma , 1981 .