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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Comunicações orais ► em encontros internacionais


Referência Bibliográfica

LAVALLÉE, Y., VARLEY, N., SPIELER, O., HESS, K-U., RICHARD, D., MUELLER, S., CORDONNIER, B., KUEPPERS, U., SCHEU, B., KREMER, S., DINGWELL, D.B. (2007) - Volcán de Colima’s recent eruptive phase: a comprehensive experimental contribution. AGU Joint Assembly, Acapulco, México, 22 - 25 de Maio (Comunicação Oral).


Volcán de Colima’s most eruptive phase of lava dome growth and explosions was investigated through an array of rheological apparatus mimicking physical processes. Samples were chosen which represent the full range of materials present in the conduit and the lava dome; this was ascertained by thorough field-based density distribution campaigns.


The viscosity of dome and conduit margin material, i.e., bubble-poor, crystal-rich lavas was investigated using a uniaxial deformation apparatus. The strain-rate dependence of viscosity presents a shear thinning rheology which favours the ascent through a conduit as a plug flow. Yet the lower viscosity of Colima’s lava (relatively less viscous than other dome growing lavas) suggest that micro-fracturing may be lesser at the range of strain rates estimated along the conduit margin.


Fragmentation and permeability measurements on inner conduit material with a high porosity were achieved through a shock-tube apparatus. For instance, the threshold for fragmentation of 24 \% porosity samples required $<$11 MPa of overpressure, whereas denser samples with 15 \% pores fragmented with only 8 MPa. This large threshold at higher porosity is explained by a higher permeability. In fact Colima samples generally exhibit a comparatively high permeability, giving rise to a low explosivity.


The results help constrain the ongoing eruptive phase. A relatively dense, yet permeable magma with low pore pressure and buoyancy slowly ascends through the conduit. Slow ascent and relatively low viscosity in turn lessen the occurrence of micro-cracking in the magmas and thus the detection of seismic activity during effusive extrusion periods. Faster effusion episodes, like that of 2004, have been accompanied by far more seismicity with a swarm of LF events occurring prior to the onset of dome growth, resulting from faster ascent. The magma was relatively degassed so did not produce a large explosion. The slow ascent and high permeability further allow significant volatile loss which prevents rapid pressure accumulations necessary for large eruptions; the activity is rather characterized by small explosions daily. The overall level of activity has been increasing since the onset of the eruptive phase in 1998 and our results suggest that progressive sealing and closing of the conduit and lowering of the permeability could lead to much stronger explosive events.