TY - JOUR
T1 - Tracking the permeable porous network during strain-dependent magmatic flow
AU - Kendrick, J. E.
AU - Lavallée, Y.
AU - Hess, K. U.
AU - Heap, M. J.
AU - Gaunt, H. E.
AU - Meredith, P. G.
AU - Dingwell, D. B.
N1 - Funding Information:
The authors would like to thank O. Spieler and S. Mueller for sample collection and N. Varley for logistical organisation. D.B. Dingwell wishes to acknowledge the support of a research professorship of the Bundesexzellenzinitiative and an advanced grant ( 247076 EVOKES) of the European Research Council . Y. Lavallée wishes to acknowledge the support of the Deutsche Forschungsgemeinschaft grant LA2191/3-1 as well as the Starter Grant SLiM ( 306488 ) of the European Research Council . We acknowledge the support of a Hubert Curien Partnership (PHC) PROCOPE grant (grant number 27061UE ) of the Deutscher Akademischer Austauschdienst (DAAD) in Germany, and the Ministry of Foreign and European Affairs (MAE) and the Ministry of Higher Education and Research (MESR) , both in France. M. J. Heap also acknowledges CNRS INSU grant “Étude de la stabilité des édifices volcaniques”.
Copyright:
Copyright 2013 Elsevier B.V., All rights reserved.
PY - 2013/6/15
Y1 - 2013/6/15
N2 - Rheological variations have been postulated as the cause of transitions from effusive to explosive volcanic eruption style. Rheology is integrally linked to the composition and textural state (porosity, crystallinity) of magma as well as the stress, temperature and strain rate operative during flow. This study characterises the rheological behaviour and, importantly, the evolution of physical properties of two magmas (with different crystallinity and porosity) from Volcán de Colima (Mexico) - a volcanic system known for its rapid fluctuations in eruption style.Magma samples deformed in a uniaxial press at a constant stress of 2.8, 12 or 24MPa, a constant temperature of 940-945°C (comparable to upper conduit or lava dome conditions) to strains of 20 or 30% displayed different mechanical behaviour and significant differences in measured strain rates (10-2-10-5s-1). The evolution of porosity, permeability, dynamic Young's modulus and dynamic Poisson's ratio illustrate a complex evolution of the samples manifested as strain-hardening, visco-elastic, constant-rate and strain-weakening deformation. Both magmas behave as shear-thinning non-Newtonian liquids and viscosity decreases as a function of strain.We find that strain localisation during deformation leads to the rearrangement and closure of void space (a combination of pores and cracks) followed by preferentially aligned fracturing (in the direction of the maximum principal stress) to form damage zones as well as densification of other areas. In a dome setting, highly viscous, low permeability magmas carry the potential to block volcanic conduits with a magma plug, resulting in the build-up of pressures in the conduit. Above a certain threshold of strain (dependent upon stress/strain rate), the initiation, propagation and coalescence of fractures leads to mechanical degradation of the magma samples, which then supersedes magmatic flow and crystal rearrangement as the dominant form of deformation. This results in lower apparent viscosities than those anticipated for magma of such crystallinity, especially at high strain rates. In a lava dome, this could result in dome collapse and the concomitant depressurisation could trigger an explosive eruption.
AB - Rheological variations have been postulated as the cause of transitions from effusive to explosive volcanic eruption style. Rheology is integrally linked to the composition and textural state (porosity, crystallinity) of magma as well as the stress, temperature and strain rate operative during flow. This study characterises the rheological behaviour and, importantly, the evolution of physical properties of two magmas (with different crystallinity and porosity) from Volcán de Colima (Mexico) - a volcanic system known for its rapid fluctuations in eruption style.Magma samples deformed in a uniaxial press at a constant stress of 2.8, 12 or 24MPa, a constant temperature of 940-945°C (comparable to upper conduit or lava dome conditions) to strains of 20 or 30% displayed different mechanical behaviour and significant differences in measured strain rates (10-2-10-5s-1). The evolution of porosity, permeability, dynamic Young's modulus and dynamic Poisson's ratio illustrate a complex evolution of the samples manifested as strain-hardening, visco-elastic, constant-rate and strain-weakening deformation. Both magmas behave as shear-thinning non-Newtonian liquids and viscosity decreases as a function of strain.We find that strain localisation during deformation leads to the rearrangement and closure of void space (a combination of pores and cracks) followed by preferentially aligned fracturing (in the direction of the maximum principal stress) to form damage zones as well as densification of other areas. In a dome setting, highly viscous, low permeability magmas carry the potential to block volcanic conduits with a magma plug, resulting in the build-up of pressures in the conduit. Above a certain threshold of strain (dependent upon stress/strain rate), the initiation, propagation and coalescence of fractures leads to mechanical degradation of the magma samples, which then supersedes magmatic flow and crystal rearrangement as the dominant form of deformation. This results in lower apparent viscosities than those anticipated for magma of such crystallinity, especially at high strain rates. In a lava dome, this could result in dome collapse and the concomitant depressurisation could trigger an explosive eruption.
KW - Damage
KW - Deformation
KW - Magma
KW - Rheology
KW - Strain localization
KW - Viscosity
UR - http://www.scopus.com/inward/record.url?scp=84880293816&partnerID=8YFLogxK
U2 - 10.1016/j.jvolgeores.2013.05.012
DO - 10.1016/j.jvolgeores.2013.05.012
M3 - Article
AN - SCOPUS:84880293816
SN - 0377-0273
VL - 260
SP - 117
EP - 126
JO - Journal of Volcanology and Geothermal Research
JF - Journal of Volcanology and Geothermal Research
ER -