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- Title
Magnetic Resonance Imaging of Multi‐Phase Lava Flow Analogs: Velocity and Rheology.
- Authors
Birnbaum, Janine; Zia, Wasif; Bordbar, Alireza; Lee, Ray F.; Boyce, Christopher M.; Lev, Einat
- Abstract
The rheology of lavas and magmas exerts a strong control on the dynamics and hazards posed by volcanic eruptions. Magmas and lavas are complex mixtures of silicate melt, suspended crystals, and gas bubbles. To improve the understanding of the dynamics and effective rheology of magmas and lavas, we performed dam‐break flow experiments using suspensions of silicone oil, sesame seeds, and N2O bubbles. Experiments were run inside a magnetic resonance imaging (MRI) scanner to provide imaging of the flow interior. We varied the volume fraction of sesame seeds between 0 and 0.48, and of bubbles between 0 and 0.21. MRI phase‐contrast velocimetry was used to measure liquid velocity. We fit an effective viscosity to the velocity data by approximating the stress using lubrication theory and the imaged shape of the free surface. In experiments with both particles and bubbles (three‐phase suspensions), we observed shear banding in which particle‐poor regions deform with a lower effective viscosity and dominate flow propagation speed. Our observations demonstrate the importance of considering variations in phase distributions within magmatic fluids and their implications on the dynamics of volcanic eruptions. Plain Language Summary: Lavas and magmas are viscous liquids whose properties control the dynamics and associated hazards of volcanic eruptions. They are comprised of multiple phases, including silicate liquids, crystals, and gas bubbles, whose interactions control lava and magma behavior. To understand how these phases interact and determine lava properties, we ran a series of lava flow analog experiments in a medical magnetic resonance imaging scanner to measure the inside of flows. We explored a range of particle (0–0.48) and bubble (0–0.21) volume fractions to consider ranges relevant to natural flows. We measured the velocity of the liquid phase in imaging planes through the middle of the setup and used the velocity to invert for suspension viscosity. In experiments containing particles, we observed the development of structures in the flow, characterized by alternating bands of high and low particle concentration. The particle‐poor regions deform more easily than we would expect for the uniform suspension and allow for faster propagation of the flow. Key Points: MRI experiments of low‐concentration bubble‐bearing suspensions resemble liquid flows and adhere to bulk rheology approximationsThree‐phase mixtures show strong shear localization even at low total volume fraction of particlesShear bands dominate flow and allow for faster flow front propagation speeds than would be expected for a homogeneous suspension
- Subjects
LAVA flows; MULTIPHASE flow; MAGNETIC resonance imaging; FLOW velocity; ELECTRORHEOLOGY; RHEOLOGY; BUBBLES
- Publication
Journal of Geophysical Research. Solid Earth, 2023, Vol 128, Issue 5, p1
- ISSN
2169-9313
- Publication type
Article
- DOI
10.1029/2023JB026464