Juvenile magma recognition and eruptive dynamics inferred from the analysis of ash time series: The 2015 reawakening of Cotopaxi volcano

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• 作者：H. Elizabeth Gaunt^a ; ^{egaunt@igepn.edu.ec} ; Benjamin Bernard^a ; Silvana Hidalgo^a ; Antonio Proa&ntilde ; o^a ; Heather Wright^b ; Patricia Mothes^a ; Evelyn Criollo^c ; Ulrich Kueppers^d
• 关键词：Volcanic ash ; Volcano monitoring ; Cotopaxi volcano ; Eruption dynamics ; Hazard assessment
• 刊名：Journal of Volcanology and Geothermal Research
• 出版年：2016
• 出版时间：15 December 2016
• 年：2016
• 卷：328
• 期：Complete
• 页码：134-146
• 全文大小：2640 K
• 卷排序：328

文摘

Juvenile ash fragments are recognized in Cotopaxi ash based on the presence of unaltered glass containing few microlites. Microprobe analysis of the fresh glass shows high analytical totals and compositions consistent with previous eruptions at Cotopaxi, but unlike compositions of the groundmass in hydrothermal material. Juvenile material in the initial explosions (Phase 1) is glassy and contains opal in contact with fresh melt preserving evidence for interaction between magma and the hydrothermal system. The componentry of ash evolved from dominantly hydrothermal and lithic material to dominantly juvenile material through the 2015 eruptive sequence. Increasingly high micro-crystallinities in the juvenile grains from phases 2-4 suggest slowing ascent rates and increasing duration of shallow storage in a system open to gas loss where fragmentation was a result of brittle breakage of a shallow magmatic plug. Geophysical signals (high LP and VT event rates, buried explosion signals, elevated SO2 emissions, detection of BrO, high SO2/H2S ratios and inflation of the volcanoes flanks) support the conclusion of the involvement of juvenile magma.