%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Colombier, M.
%A Bernard, B.
%A Wright, H.
%A Le Pennec, Jean-Luc
%A Caceres, F.
%A Cimarelli, C.
%A Heap, M. J.
%A Samaniego, Pablo
%A Vasseur, J.
%A Dingwell, D. B.
%T Conduit processes in crystal-rich dacitic magma and implications for eruptive cycles at Guagua Pichincha volcano, Ecuador
%D 2022
%L fdi:010086409
%G ENG
%J Bulletin of Volcanology
%@ 0258-8900
%K Guagua Pichincha ; Eruptive cycles ; Textural analysis ; Plinian eruption ; Dome-forming eruption ; Effusive-explosive transition ; Degassing ; Percolation model
%K EQUATEUR
%M ISI:000884746100001
%N 12
%P 105 [23 ]
%R 10.1007/s00445-022-01612-1
%U https://www.documentation.ird.fr/hor/fdi:010086409
%> https://horizon.documentation.ird.fr/exl-doc/pleins_textes/2023-01/010086409.pdf
%V 84
%W Horizon (IRD)
%X 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 similar to 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.
%$ 064 ; 066