Conduit processes in crystal-rich dacitic magma and implications for eruptive cycles at Guagua Pichincha volcano, Ecuador

Mathieu Colombier; Benjamin Bernard; Heather M. Wright; Jean-Luc Le Pennec; Francisco Caceres; Corrado Cimarelli; Michael J. Heap; Pablo Samaniego; Jeremie Vasseur; Donald B. Dingwell

doi:10.1007/s00445-022-01612-1

USGS · 70247864

Conduit processes in crystal-rich dacitic magma and implications for eruptive cycles at Guagua Pichincha volcano, Ecuador

Mathieu Colombier·Benjamin Bernard·Heather M. Wright·Jean-Luc Le Pennec·Francisco Caceres·Corrado Cimarelli·Michael J. Heap·Pablo Samaniego·Jeremie Vasseur·Donald B. Dingwell

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Abstract

Stratovolcanoes are commonly characterised by cyclic eruptive activity marked by transitions between dome-forming, Vulcanian, Subplinian and Plinian eruptions. Guagua Pichincha volcano (Ecuador) has been a location of such cyclicity for the past ~ 2000 years, with Plinian eruptions in the first and tenth centuries AD (Anno Domini/after Christ), and CE (Common Era) 1660, which were separated by dome-forming to Subplinian eruptions, such as the recent 1999–2001 eruption. These cycles are therefore a prominent example of effusive-explosive transitions at varying timescales. Here, we investigate the reasons for such shifts in activity by focusing on degassing and outgassing processes within the conduit. We have coupled a petrophysical and textural analysis of dacites from the CE 1660 Plinian eruption and the 1999–2001 dome-forming/Vulcanian eruption, with different percolation models in order to better understand the role of degassing on eruptive style. We demonstrate that the transition from dome-forming to Plinian activity is correlated with differences in phenocryst content and consequently in bulk viscosity. A lower initial phenocryst content and viscosity is inferred for the Plinian case, which promotes faster ascent, closed-system degassing, fragmentation and explosive activity. In contrast, dome-forming phases are promoted by a higher magma viscosity due to higher phenocryst content, with slower ascent enhancing gas escape and microlite crystallization, decreasing explosivity and yielding effusive activity.

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Bulletin of Volcanology Article

Source-reported bounding extent: 0.45944639801014375° to 0.9806815363857169° latitude; -77.96144509158114° to -77.4628312552756° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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Mathieu Colombier, Benjamin Bernard, Heather M. Wright, Jean-Luc Le Pennec, Francisco Caceres, Corrado Cimarelli, Michael J. Heap, Pablo Samaniego, Jeremie Vasseur, Donald B. Dingwell. 2022-11-16. Conduit processes in crystal-rich dacitic magma and implications for eruptive cycles at Guagua Pichincha volcano, Ecuador. https://doi.org/10.1007/s00445-022-01612-1

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