The transition from endogenous to exogenous growth of lava domes with the development of shear bands

Abstract:The 1995-present eruption of Soufrière Hills Volcano on Montserrat has produced over a cubic kilometre of andesitic magma, creating a series of lava domes that were successively destroyed, with much of their mass deposited in the sea. There have been five phases of lava extrusion to form these lava domes: -March 1998-July 2003 August 2005-April 2007July 2008-January 2009 and October 2009-February 2010. It has been one of the most intensively studied volcanoes in the world during this time, and there are long instrumental and observational datasets. From these have sprung major new insights concerning: the cyclicity of magma transport; low-frequency earthquakes associated with conduit magma flow; the dynamics of lateral blasts and Vulcanian explosions; the role that basalt-andesite magma mingling in the mid-crust has in powering the eruption; identification using seismic tomography of the uppermost magma reservoir at a depth of 5.5 . 7.5 km; and many others. Parallel to the research effort, there has been a consistent programme of quantitative risk assessment since 1997 that has both pioneered new methods and provided a solid evidential source for the civil authority to use in mitigating the risks to the people of Montserrat.At the time of writing (January 2013), the Soufrière Hills Volcano (SHV) is in its 17th year of eruption, placing it with a select group of very long-lived eruptions from silicic volcanoes. Within the Caribbean plate, only two other silicic volcanoes have had longer-lived historical extrusive eruptions: Santiaguito, Guatemala (1922( -present: Harris et al. 2003 and Arenal, Costa Rica (1968 -present: Wadge et al. 2006). As with both of these volcanoes, SHV has not extruded lava continuously for the whole eruption, but has erupted intermittently. In fact, it has been extruding lava for a cumulative total of only 8.5 years out of 17. So in what sense can we consider this a single eruption rather than a series of shorter ones? The longest gaps between extrusive phases have been about 2-3 years (July 2003-August 2005 February 2010-present). However, during the pauses between extrusion at SHV, there have been many indications that the volcanic system remains active. These have included inflation of the island's surface, the release of volatiles in quantities similar to those seen during lava extrusion, swarms of low-frequency seismicity, explosions and the production of ash. This suggests that there are processes within the system responsible for producing alternating extrusive and non-extrusive states. Melnik & Sparks (2005) showed theoretically how non-linear response to relatively minor perturbations of the magmatic system can result in such behaviour.Recognition of the long-term continuity of the eruption process has direct consequences for the tasks of monitoring and estimating the risks posed by the volcano. It means that the Montserrat Volcano Observatory (MVO) must monitor the volcano continuously, even during periods of relative quiescence and apparent inactivity. The probabil...

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“…The transition from endogenous to exogenous growth (cf. Hale & Wadge 2008) occurred in November 2005 ( Fig. 1.9).…”

Section: Phase 3 (1 August 2005 -20 April 2007)mentioning

confidence: 97%

Chapter 1 An overview of the eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010

Wadge

Voight

Sparks

et al. 2014

Memoirs

139

119

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“…Moreover, the growth of a lava spine occurred only once during the last 12 years, showing that strong shear localization has not been typical (e.g. Hale and Wadge 2008). To avoid this, the strain rates near the conduit margins must have been relatively low (presumably within the ductile field below~10 −4 s −1 ), especially considering the shear thinning rheological properties of the magma.…”

Section: Eruption-style Transitionmentioning

confidence: 99%

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

Lavallée¹,

Varley

Alatorre‐Ibargüengoitia

et al. 2011

Bull Volcanol

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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 Editorial responsibility: M.A. Clynne

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“…As a consequence, this model is only suitable for considering lava dome growth that replicates the large-scale structure and not the fine-scale detail. Modelling localised and hence exogenous dome growth would require additional physics, such as the development and evolution of shear bands and flow discontinuities, whose initiation and evolution are poorly constrained (Hale and Wadge, 2008).…”

Section: Computational Modelmentioning

confidence: 99%

Modelling the lava dome extruded at Soufrière Hills Volcano, Montserrat, August 2005–May 2006

Hale

Calder

Wadge

et al. 2009

Journal of Volcanology and Geothermal Research

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Lava domes comprise of core, carapace, and clastic talus components. They can grow endogenously by inflation of a core and/or exogenously with the extrusion of shear bounded lobes and whaleback lobes at the surface. Internal structure is paramount in determining the extent to which lava dome growth evolves stably, or conversely the propensity for collapse. The more core lava that exists within a dome, in both relative and absolute terms, the more explosive energy is available, both for large pyroclastic flows following collapse and particularly for lateral blast events following very rapid removal of lateral support to the dome. Knowledge of the location of the core lava within the dome is also significant for hazard assessment purposes. A spreading toe or lobe of core lava over a talus substrate may be both relatively unstable and likely to accelerate to more violent activity during the early phases of a retrogressive collapse.Soufrière Hills Volcano, Montserrat has been erupting continuously since 1995 and has produced numerous lava domes which have suffered collapse events. We consider one continuous dome

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The transition from endogenous to exogenous growth of lava domes with the development of shear bands

Cited by 70 publications

References 49 publications

Chapter 1 An overview of the eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010

Chapter 1 An overview of the eruption of Soufrière Hills Volcano, Montserrat from 2000 to 2010

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

Modelling the lava dome extruded at Soufrière Hills Volcano, Montserrat, August 2005–May 2006

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