Papers by Mikhail Sindang
Geology
One of the biggest challenges in volcanology is assessing the role of magma properties (volatile ... more One of the biggest challenges in volcanology is assessing the role of magma properties (volatile budgets, storage depths, and ascent rates) in controlling eruption explosivity. We use a new approach based on apatite to estimate volatile contents and magma ascent rates from a sequence of sub-Plinian, effusive, and Vulcanian eruption deposits at Rabaul caldera (Papua New Guinea) emplaced in 2006 CE to probe the mechanisms responsible for the sudden transitions in eruption styles. Our findings show that all magmas were originally stored at similar conditions (2–4 km depth and 1.8–2.5 wt% H2O in the melt); only the magma that formed the lava flow stalled and degassed at a shallower level (0.2–1.5 km) for several months. A more energetic batch of magma rose from depth, bypassed the transient reservoir, and ascended within ≤8 h to Earth's surface (mean velocity ≥0.2 m/s), yielding the initial sub-Plinian phase of the eruption. The shallowly degassed magma was then able to reach the su...
Sample description and whole-rock chemistry for rocks from the Rabaul Pyroclastics and 2014 erupt... more Sample description and whole-rock chemistry for rocks from the Rabaul Pyroclastics and 2014 eruptions of Rabaul, Papua New Guinea.
<p>Caldera-forming eruptions are some of the most devastating events on Earth; however, the... more <p>Caldera-forming eruptions are some of the most devastating events on Earth; however, the volcanoes that produce these eruptions frequently have much more minor activity. Knowing if a restless caldera is currently primed for a large eruption, therefore, has important implications for hazard assessment and risk management. Many calderas, including Rabaul in Papua New Guinea, show cycles of activity with multiple caldera-forming eruptions interspersed with more minor activity. We present data that spans an entire cycle, from one caldera-forming eruption to the next and estimate the storage conditions for each eruption. The last complete caldera cycle of Rabaul started at ~10.5 ka, with the eruption of the dacitic Vunabugbug Ignimbrite. Following the Vunabugbug, little volcanic activity was preserved until ~4.4 ka, suggesting either a period quiescence or destruction and burial during the subsequent caldera-forming eruptions of the region. From 4.4 ka, there is an increase in the volume and SiO<sub>2</sub> contents of volcanic deposits that are preserved, which culminated in the eruption of the dacitic Memorial Ignimbrite at ~4.1&#160;ka. The Memorial Ignimbrite was smaller than the Vunabugbug Ignimbrite and Rabaul Pyroclastics and may not have formed a caldera; however, it does appear to have altered the plumbing system and allowed deeper, hotter basalts to reach the surface. Following the eruption of these basalts, the system gradually evolves towards more silicic magmas, until the eruption of the dacitic Rabaul Pyroclastics at ~1.4&#160;ka. After the Rabaul Pyroclastics hotter, more mafic magmas can again reach the surface, both as more mafic lava flows and as hybrid andesites that contain crystal cargos transported from deeper in the system.</p><p>Two-pyroxene, clinopyroxene&#8211;liquid and plagioclase&#8211;liquid thermobarometers suggest that the dacites, including those erupted during the caldera-forming eruptions, were stored at pressures of ~1&#160;kbar (~4&#160;km depth) and at temperatures of ~930&#160;&#176;C. There is a tight relationship between the temperature and the SiO<sub>2</sub> content of the magmas, with the basalts erupted after the large ignimbrites recording temperatures of up to 1100&#160;&#176;C. Some of the more mafic magmas also record deeper storage, at pressures of 3&#8211;4&#160;kbar (11&#8211;15&#160;km). Plagioclase&#8211;liquid pairs suggest melt H<sub>2</sub>O contents of ~2.8&#160;wt.% for the dacites, although some of the more mafic magmas have slightly higher melt H<sub>2</sub>O contents (3.2&#8211;4.0 wt.%)&#8212;this may be because the basalts were saturated and stored at greater pressures. Magnetite&#8211;liquid pairs record relatively constant oxygen fugacities of ~1.2 log units above the FMQ buffer.</p><p>At Rabaul it would take on the order of a few millennia to differentiate or accumulate enough dacitic magma to produce a large explosive eruption. The eruption of highly evolved, crystal-poor, cold, hydrous magmas geochemically similar to those erupted prior to the Memorial Ignimbrite and Rabaul Pyroclastics may provide a warning of an impending large explosive eruption.</p>
Journal of Volcanology and Geothermal Research, 2020
The size of eruptions from calderas varies greatly, from small effusive eruptions that pose dange... more The size of eruptions from calderas varies greatly, from small effusive eruptions that pose danger only in the immediate vicinity of the vent, to large, caldera-forming events with global impact. However, we currently have little way of knowing the size of the next eruption. Here, we focus on Rabaul Caldera, Papua New Guinea, to investigate differences between the magmatic processes that occurred prior to the N11-km 3 caldera-forming "1400 BP" Rabaul Pyroclastics eruption and prior to subsequent, smaller (b1 km 3) post-caldera eruptions. During the current, post-caldera phase, basaltic enclaves and mafic minerals are common among the erupted products, indicating basalt has been free to enter the mobile, dacite-dominated region of the sub-caldera plumbing system. Many of the post-caldera magmas are hybrid andesites, reflecting the importance of mixing and mingling of basaltic and dacitic magmas during this period. In contrast, before the Rabaul Pyroclastics eruption, the recharge was an andesite that was not the product of mixing basalt and dacite. The lack of basaltic recharge prior to the Rabaul Pyroclastics eruption suggests basalt was prevented from entering the shallow, sub-caldera magma system at that time, possibly by the presence of a large, silicic, melt-dominated body. That basalt can currently enter the shallow system is consistent with reduced thermal and rheological contrasts between the recharge and resident magma, implying a similar large silicic melt body currently does not exist beneath the caldera. If this hypothesis is correct, it may be possible to track the growth and evolution of large magma reservoirs that feed caldera-forming eruptions by monitoring the petrology of eruptive products.
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Papers by Mikhail Sindang