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Understanding Basaltic Plinian Activity at Masaya Caldera, Nicaragua
Bamber EC, Arzilli F, Polacci M, La Spina G, Petrelli M, Hartley ME, Di Genova D, Fellowes J, Chavarria D, Saballos JA, De' Michieli Vitturi M & Burton MR
Bamber EC, Arzilli F, Polacci M, La Spina G, Petrelli M, Hartley ME, Di Genova D, Fellowes J, Chavarria D, Saballos JA, De' Michieli Vitturi M & Burton MR (2020) Goldschmidt Abstracts, 2020 117
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05d: Room 2, View in program
Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.
HI Emily, nice and interesting work. Have you estimated the ascent rate? Do you have any idea on the main factors switching to a basaltic Plinian eruption (e.g., pre-eruptive condition, conduit geometry)?
Hello Chiara, this is a great question! I think it is difficult to determine the ascent rate, particularly as we do not expect a constant rate during the ascent, but we can make an estimate from the constraints on the timescale of syn-eruptive microlite crystallisation and depth of the system, which provides an average ascent rate on the order of 10s of m/s. This ascent rate is comparable with other basaltic Plinian eruptions and does point to a role of fast magma ascent in basaltic Plinian activity. Regarding the main factors which may promote explosive rather than effusive activity, there appears to be a role of low-moderate pre-eruptive storage temperatures and its role in driving high undercooling and rapid crystallisation. The influence of conduit geometry is interesting to explore, however there is unfortunately less information on the conduit structure and vent location, especially looking at older eruptions such as that of the Fontana Lapilli (60 ka). However, these are great factors to investigate in greater detail.
Thank you Emily for your presentation! Understanding of dynamics driving Plinian eruptions at basaltic volcanic systems is really a challenge for the modern volcanology. We have similar examples here in Italy at Mt. Etna, as you mentioned in the presentation. What moves the volcanic system from an effusive or low-to-moderate explosivity towards highly vigorous and energetic eruptions still remains poorly understood. Fast ascent? Tectonically-driven changes in the conduit geometry? In any case, transitions seem to be driven by modifications in the recharge/discharge rate of magma/gas in the plumbing system. Although the two issues can be strictly correlated, are there other indications for Masaya leading to disambiguation about the role of conduit processes (what processes) vs. fast ascent?
Hello Marco, thank you for your great question! Identifying and understanding the driving mechanisms of basaltic Plinian activity at systems such as Masaya and Etna is definitely an interesting challenge. Fast ascent seems to play a role in driving basaltic Plinian activity, also from comparison with studies which estimate an ascent rate for the Fontana Lapilli and Etna eruptions. Also a low-moderate pre-eruptive storage temperature, promoting high undercooling and rapid syn-eruptive crystallisation can drive rheological change within the conduit, magma fragmentation and a resulting Plinian eruption. Looking at the influence of conduit geometry may be more difficult for Masaya when studying its past Plinian activity, especially for the Fontana Lapilli eruption. However, the tectonic setting of the Masaya area may suggest an influence of tectonic changes through time on the transition in activity at Masaya. Modifications in the recharge/discharge rate of magma/gas is a very interesting point in driving explosive activity, constraining the volatile budget of these eruptions and investigating the role of volatiles such as CO2 will be very helpful to assess this contribution.
Hi Emily, great presentation! In your Masaya Triple Layer samples, the adjacent microlite-poor and microlite-rich sections bounded by oxides are quite interesting! Do you have any hypotheses for what might be causing these heterogeneous inter-mingling regions of 20 to 50 vol% microlite content? In our study at Masaya we speculate that a temporary or partial sealing of the conduit may lead to transition to explosive behavior. When the seal breaks and triggers rapid ascent, perhaps some kind of temperature gradient may occur with respect to the conduit wall?
Hello Lisa, thank you for your question, the cause of the textural heterogeneity in the Masaya samples is very interesting! I think that these inter-mingling regions could represent conduit zonation, possibly in relation to velocity or temperature, which could enable the stagnation, degassing and crystallisation of the microlite-rich end member in closer proximity to the conduit wall. A temperature gradient could facilitate more extensive crystallisation with respect to a hotter, rapidly ascending central flow of lower viscosity, microlite-poor magma. The effect of this heterogeneity on conduit dynamics is very interesting and could contribute to sealing within the conduit.
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