Quantifying the crystalline-scale signatures of volcano-scale magma dynamics through multiphase fluid and thermodynamic modeling
- Given the inaccessibility of directly observing most magmatic processes, one of the main challenges in volcanism is deciphering the accessible data. For example, crystals in erupted magma can provide a testimony of magmatic processes. However, relying on either crystalline scale observations to describe a system scale process or system scale observations to describe a crystalline scale process is challenging. This is because different scales can either compound or breakdown to impact other scales and, ultimately, impact the observable data. In Part I of the thesis, we quantifying how a crystalline scale process of crystal-crystal interactions can compound to impact system scale processes of fractional crystallization (a reaction, segregation process that explains magma evolution) and magma convection. In Part II of the thesis, we describe how a crystalline scale process can impact crystalline data, namely crystal zonations. In Part III of the thesis, we explore how a system scale shearing instability along lava flows can trigger a crystalline scale processes of crystal formation. In Part IV of the thesis, we model how remote imaging techniques can potentially image either small or large scale melting processes on cryomagmatic bodies like Jupiter's moon, Europa. In order to address one of the grand challenges in volcanology, I use and develop multiscale and multiphysics models that are testable against field data. For Part I, we model the cooling and crystallization of both hot basaltic and dacitic magmas after being injected into a cold magma reservoir. We couple the magma dynamics at the crystalline scale to the thermodynamic processes governing crystal formation and melt property variation. We resolve the physics of individual crystal interactions as they settle. By resolving the individual crystals, we can capture the testimony each of the crystals provide during their crystal zonations to then compare to observational data. Our results show that crystal-crystal interactions at low crystallinity magma can compound and drive convection, as well as, fractional crystallization. In response to driving system-scale dynamics, the crystalline scale process then impacts crystalline scale data. In Part II, we look at how crystalline scale process, impacts crystalline scale data. Cross sections of crystals provide a unique history into the magmatic environments crystals sample through their history. As crystals grow and shrink, they record compositional changes as crystal zonations. One of the benefits of using crystalline scale modeling techniques is we can then record the resulting observations at the crystalline scale and predict the observations associated with crystal driven convection. Our results show that crystals record complex and unique zonations in the crystalline-scale domain, suggesting that zonations and their heterogeneity can be indicative of local instead of system scale processes. Also, our results show that many of the crystals in the instability dissolve and lose their thermal record of the instability. These results highlight the challenges of deciphering system-scale process from crystalline data. For Part III, we look at how a system scale process of a shearing instability may result in crystalline scale observations. Specifically, we use a linear stability analysis of a shearing instability to better understand what may be triggering a rheological transition along a lava flow. Basaltic lavas begin flowing as pāhoehoe but sometimes transition into 'a'ā. Field observations and previous models have clearly demonstrated that the rheology of smooth, liquid-like pāhoehoe is distinct from rough, pasty 'a'ā, but the cause of this dramatic and rapidly occurring change in rheology has remained unclear. The pāhoehoe to 'a'ā transition could be initiated by internal shear instability in layered pāhoehoe flow. We use a linear stability analysis to understand how lava properties like relative flow speed, layer thickness, and viscosity can impact whether the instability occurs. The conditions under which the instability arises depend on both extrinsic and intrinsic factors. We test the model's prediction of stable flow configurations against field observations of solidified lava flows. For Part IV, I model different melt conditions within Europa's icy crust to determine whether the recently deployed ice penetrating radar instruments would be able to detect the eutectic zone, a region where melt and solid water phases are both in equilibrium. We use a suite of simple water configurations and scattering models to bound the eutectic detectability in terms of its effective reflectivity. We find that, for each configuration, a range of physically plausible eutectic parameters exist that could produce detectable echoes and further help characterize the eutectic zone.
|Type of resource
|electronic resource; remote; computer; online resource
|1 online resource.
|Pamukcu, Ayla Susan
|Degree committee member
|Pamukcu, Ayla Susan
|Degree committee member
|Stanford University, Department of Geophysics
|Statement of responsibility
|Submitted to the Department of Geophysics.
|Thesis Ph.D. Stanford University 2021.
- © 2021 by Cansu Culha
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