Highly explosive 2010 Merapi eruption: Evidence for shallow-level crustal assimilation and hybrid fluid

Abstract

samples documents the release of an aqueous fluid enriched in Cl, Na, Ca, Cd, Sb and Zn during the paroxysmal subplinian eruption. The paroxysmal eruption may have been produced by saturating the pre-eruptive basaltic andesite magma with this hybrid aqueous carbonic NaCl-HCl-rich fluid due to bulk assimilation creating high partial pressure of CO 2 at shallow crustal conditions of about 200 MPa. In contrast, mildly explosive block-and-ash flows (typical Merapi-type) may result from incomplete (selective) assimilation of the carbonatebearing xenoliths and lower CO 2 partial pressure that may not lead to explosive degassing.

Pre- and syn-eruptive degassing and crystallisation processes of the 2010 and 2006 eruptions of Merapi volcano, Indonesia

“…Large increases of CO 2 /SO 2 , CO 2 /HCl and CO 2 /H 2 O were detected in fumarolic gases in the months leading up to the 2010 eruption, with a dramatic increase in CO 2 abundance from 10 mol% in September 2010 up to 35-63 mol% on 20 October, interpreted to be due to a progressive shift to degassing of a deeper magmatic source (Surono et al 2012). CO 2 fluxing is a process that likely takes place at Merapi and occurred prior to the 2010 and 2006 eruptions, both from depth and from the crust (Surono et al 2012;Borisova et al 2013;Troll et al 2013). However, isobaric dehydration due to CO 2 fluxing should result in melt inclusion compositions positioned along isopleth lines on a H 2 O-CO 2 plot and show a relatively continuous range of H 2 O and CO 2 contents (Reubi et al 2013).…”

“…Previous workers (e.g. Chadwick et al 2007;Deegan et al 2010;Troll et al 2012Troll et al , 2013Borisova et al 2013) have proposed that CO 2 liberation via crustal carbonate assimilation has the potential to sustain and intensify eruptions at Merapi. Monitoring data of the 2010 eruption indicate large CO 2 emissions prior to the 2010 eruption (Surono et al 2012), and previous melt inclusions have been interpreted to reflect CO 2 fluxing at Merapi (Nadeau et al 2013).…”

“…In addition, crustal carbonate assimilation and the resulting CO 2 liberation has also been invoked to play a significant role in governing the explosivity of eruptions (Chadwick et al 2007;Deegan et al 2010;Troll et al 2012Troll et al , 2013Borisova et al 2013). Secondary ion mass spectrometry (SIMS) volatile data (CO 2 , H 2 O, F, Cl, S) of Merapi clinopyroxene and amphibole-hosted silicate melt inclusions in lava and scoria from unknown eruptive origins have recently been published by Nadeau et al (2013).…”

Preexplosive conduit conditions during the 2010 eruption of Merapi volcano (Java, Indonesia)

“…This led to the hypothesis that the minor amount of 2010 magma involved in this event was responsible for its highly explosive nature [Surono et al, 2012]. The involvement of large amounts of carbonates and CO 2 was at first evoked as a possible cause of the 2010 explosivity [Deegan et al, 2010;Borisova et al, 2013], but recent petrologic evidences concur that the role of carbonates was not abnormal [Costa et al, 2013;Erdmann et al, 2016]. The cryptodome created degassing conditions that seem similar to those of the previous domes, which suggests that the upper part of the conduit did not sustain unusually high overpressure [Kushnir et al, 2016].…”

The 2010 explosive eruption of Java's Merapi volcano—A ‘100-year’ event

“…585 Some of the CO 2 and H 2 S escaped to the surface via a permeable fracture network and was 586 detected at Merapi's high temperature fumaroles, providing an early warning. Did this new 587 mafic magma rise to higher level and remobilize a more differentiated magma, alreadylikely (there is evidence of magma mixing in samples from Merapi, see Borisova et al, 2011), 590 this question requires further petrological studies that might, for instance, constrain the timing 591 of mixing to just before the eruption as documented at Pinatubo (Pallister et al, 1996) Emissions increased again significantly on 3 November, simultaneously with increasing 605 tremor amplitude, and peaked during the climactic explosive eruptions of 4-5 November. 606…”