Jade Bowers – Boise State University, USA
Volcanoes are like gifts to geochemists… they take materials produced deep within the Earth and move them up towards the surface, where we can unravel their fascinating life stories!
Arc volcanoes are home to some of the Earth’s most explosive eruptions. They are also one of the main places where subduction zone research interacts with broader societal interests. The staging areas of these eruptions are the magma reservoirs which lay beneath them. Each eruption is influenced by the storage conditions and any open-system processes occurring within these staging areas, which ultimately controls what we observe and experience on the surface.
My research interests lie in understanding how magma is stored and the processes associated with volcanic eruptions. At Boise State University, I integrate petrology, geochemistry, thermodynamics and statistical modeling to investigate the processes that govern the magma reservoirs beneath arc volcanoes. Using the past to inform the future is an integral component of volcanic hazard mitigation. Understanding the storage conditions beneath a volcano that has already erupted, and identifying the processes occurring within the magma reservoir prior to eruption, plays a critical role in informing monitoring systems and hazard mitigation plans.
Throughout my studies, I have been fortunate enough to work at two active arc volcanoes – Sinabung Volcano (Sumatra, Indonesia) and Llaima Volcano (Chile). As part of my Masters, I worked on the May 2016 Sinabung dome collapse, where I utilized in-situ mineral chemistry, thermobarometry, and statistical modeling to investigate the origin of magmatic enclaves observed within the lavas (Figure 1). Magmatic enclaves are typically recognized as clear evidence of magma mixing prior to an eruption. However, the preferred explanation of origin for these particular magmatic enclaves is varying degrees of disaggregation of the crystal-mush network laying beneath Sinabung Volcano (Bowers et al., submitted; Figure 2).
Figure 2. A possible model for the formation of enclaves and different glomerocrysts in the Sinabung magma based on textural observations and mineral-mineral thermobarometry. Some of the samples are disaggregates of a crystal mush deeper in the magma system while others are disaggregating from a shallow reservoir.
Llaima Volcano is now my natural laboratory, where I collected pyroclasts from extensive mafic ignimbrite exposures that were emplaced during a large volume explosive eruption (Figure 3). Mafic magmas are the most common type of magma to erupt on Earth, yet their low viscosity typically prevents mafic eruptions from being explosive. However, when they do occur, explosive mafic eruptions are among Earth’s most hazardous volcanic phenomena – the rapid rates of magma ascent mean early detection and warning systems are limited.
Like Annabelle Foster (Durham University) discussed in her ECR Story, volcanologists can use pyroclasts to investigate magma storage and ascent prior to eruptions. My colleagues at Boise State University use macrotextures of the pyroclasts and microtextures observed in the glass and bubble networks to investigate the processes occurring within the conduit after the initiation of an eruption (Marshall et al., under review; Valdivia et al., under review). In my research, I use the geochemistry of the pyroclasts and of the primary mineral phases and melt inclusions, combined with thermodynamic and statistical modeling, to understand the mafic magma’s storage conditions and identify potential open-system processes that may have led to the explosive eruption of an otherwise typically non-explosive mafic magma. An example of an open-system process is the introduction of new magma into a magma reservoir (e.g. magma mixing).
In many ways, the mineral phases present in the pyroclasts are the stars of the show. During their existence, minerals record information about the storage and open-system processes they undergo as they grow, in the form of compositionally varying zones of mineral growth. In this sense, these different zones act like tree rings recording the life story of the mineral. We can thus explore magmatic history through in-situ geochemical analysis of the mineral zones, from core to rim of the crystal (Figure 4). These mineral compositions are used as inputs into thermobarometric calculations – based on chemical equilibrium conditions, these calculations determine the pressure or temperature that the mineral crystallized at. This information can then be used to inform interpretations of the magma storage conditions where the crystal grew (e.g., converting crystallization pressure to the depth of crystallization; Figure 5).
In addition to changes in magma storage conditions, open-system processes can also result in the formation of new compositional crystal growth zones, in response to open-system processes changing the crystal’s changing environment. Magma mixing is recognized as reverse zoning in the crystal; normal zoning is the typical progression of a mineral’s composition as magma cools and crystallizes (e.g., decreases in compatible elements as they are depleted during crystallization).
Later, the compositional profile of the outermost zone boundary can be used to calculate the time between zone crystallization and eruption using a geological technique known as diffusion chronometry. We then use this timing information to determine if these perturbations resulted in eruption initiation.
The Llaima project is in its early stages of geochemical characterization and mineral grain mount preparation. We are looking for evidence of conditions or processes that indicate why this mafic center, Llaima Volcano, erupted explosively. We hope that there will be many mineral compositions and zoning profiles to share soon, so keep an eye out!
Jade Bowers (firstname.lastname@example.org) is a Ph.D. candidate at Boise State University, USA. During her masters, Jade investigated the texture and crystal chemical stratigraphy of the lavas and intermingled mafic enclaves from the May 16th 2016 Sinabung Volcano dome collapse. Her research focused on magma storage and dynamics within arc volcanoes using multi-pronged petrologic forensic studies to understand how the magma is assembled, evolves, and is mobilized to the surface.
Jade now focuses on investigating the transcrustal conditions that led to the large, mafic eruption of the Curacautin ignimbrite at Llaima Volcano, Chile, with a particular interest in understanding why all mafic centers do not produce explosive Plinian eruptions.
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