Magmatic architecture of dome-building eruptions at Volcán de Colima, Mexico

• Published in: Bulletin of volcanology Vol. 74; no. 1; pp. 249 - 260
• Main Authors: Lavallée, Yan, Varley, N. R., Alatorre-Ibargüengoitia, M. A., Hess, K.-U., Kueppers, U., Mueller, S., Richard, D., Scheu, B., Spieler, O., Dingwell, D. B.
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer-Verlag 01.01.2012; Springer; Springer Nature B.V
• Subjects: Crystalline rocks; Earth and Environmental Science; Earth Sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Exact sciences and technology; Geology; Geophysics/Geodesy; Igneous and metamorphic rocks petrology, volcanic processes, magmas; Magma; Mineralogy; Natural hazards: prediction, damages, etc; Permeability; Porosity; Research Article; Rheology; Sedimentology; Volcanoes; Volcanology; Mexico; Colima Mexico; Fragmentation energy; Failure forecast method; Ascending magma; Rheology; Lava dome; Volcán de Colima; Explosive eruptions; Porosity; Permeability; pyroclastic flows; domes; shallow depth; North America; fragmentation; homogeneity; lava; instruments; deformation; craters; fragments; explosions; flow; eruptive cycles; density; porosity; explosive eruptions; magmas; lead; vents; extrusions; physicochemical properties; buildings; plugs; growth; style
• ISSN: 0258-8900; 1432-0819
• DOI: 10.1007/s00445-011-0518-4

Changes in the physical, chemical and rheological properties of ascending magma regulate the style of volcanic eruptions. Volcán de Colima’s eruptive cycles of lava dome growth and explosions have been thoroughly monitored during the period 1998–2010 and provide a remarkable opportunity for deepening our understanding of the underlying processes responsible for the evolution of magma properties. Here, we integrate direct observation with analytical and experimental data to: (1) constrain the configuration of the shallow plumbing system and its influence on eruptive activity, (2) describe the rheological behaviour of the magma and (3) assess the conditions that lead to fragmentation and, ultimately, to explosive eruptions. The configuration of the shallow plumbing system was inferred from direct observation of extrusion sites and porosity of the erupted products. During the ongoing eruptive phase, magma was never extruded from a central vent: Both explosive and effusive activities were restricted to discrete vents inside the crater. Extensive field-based density measurements on 500 blocks in pyroclastic flow deposits reveal a bimodality of porosity at values of 12 and 26 vol.%. The least porous rocks tend to be altered, whereas the more porous rocks are pristine. This bimodal distribution, combined with the lack of a central vent, suggests the presence of a central, dense, altered plug, the fragments of which are entrained during explosive eruptions. During effusive periods, the plug appears to deflect the ascent of magma at a shallow depth and, consequently, the site of lava extrusion. The rheological properties and deformation-induced seismogenic behaviour of the magmas were investigated using a uniaxial deformation apparatus instrumented with acoustic sensors. The homogeneity in the physicochemical properties of the erupted magma permits the description of a flow law at eruptive temperature and strain rate conditions. The crystal-rich magma of Volcán de Colima exhibits a shear thinning rheology and becomes increasingly brittle at higher strain rates. Complete failure of magma can be predicted using the material failure forecast method, which integrates the acceleration of released acoustic energy throughout the deformation. Rapid decompression experiments of samples pressurised with argon were performed to assess the fragmentation conditions under which explosive eruptions progress. In the absence of gas loss due to permeable flow, the pore pressure required to fragment volcanic products is inversely proportional to the porosity. At Volcán de Colima, a rapid decompression of >6 MPa is required to fragment magma averaging 26 vol.% pores and to thereby instigate an explosive eruption. Analysis of ballistic impacts (4–6 km away from the vent) from recent explosive eruptions further requires decompression as great as 20 MPa, which is sufficient to disrupt the more porous material as well as a fraction of the denser plug. The continuing growth of a lava dome and of a larger, more impermeable plug could have consequences for the stability of the edifice and development of stronger and more erratic explosive activity at Volcán de Colima.