https://www.amandalindoo.com/nonlinear-decompression daily 0.75 2024-08-16 https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616749949827-9KBUNFM6XS1D7RRLZSMJ/Fig4.png Non-linear decompression - High crystal number densities from mechanical damage. Crystal and vesicle textures in volcanic eruption products offer crucial insights into magmatic processes. Crystals play a significant role in the nucleation and growth of gas bubbles, influencing the overall degassing efficiency of magma and, consequently, the intensity of volcanic eruptions. Therefore, pyroclast textures are often analyzed and compared with experimental results obtained under controlled conditions to establish threshold conditions that can trigger shifts in eruptive style. A longstanding puzzle in this field is the presence of numerous tiny crystals, or microlites, in dome and cryptodome samples. Despite extensive efforts, experiments have typically failed to replicate this texture, with observed number densities often an order of magnitude lower than those found in natural pyroclasts (see figure). In Lindoo and Cashman (2021)*, we introduced pressure fluctuations into decompression experiments to simulate the decompression of magma that stalls during ascent and the pressure cycling that occurs in non-erupted magma within the conduit during episodic explosive activity. These pressure fluctuations caused fragile, dendritic microlites formed at lower pressures to break apart, leading to an apparent increase in number density (hatched [D2] symbols in figure), matching the higher densities observed in natural samples. This was a significant departure from the results of experiments that followed a more traditional decompression pathway (gray symbols in figure). We then compared our experimental results with samples from the May 18, 1980, Mount St. Helens blast dacite deposit. Our findings provide an explanation for the crystal textures observed in precursory ash and the blast deposit, offering valuable insights into the degassing history of the cryptodome. https://www.amandalindoo.com/where daily 0.75 2024-08-16 https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616671272187-39F9ZDYH0QTNP4ONQYSA/IMG_2787.jpg Where? https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616671376443-4SOAYQ7AYK8HMV78R2ON/20210216_104804593_iOS.jpg Where? https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616670164321-16PYH9YPCE7N7QXD4X99/Lindoo_UAF.jpg Where? Photo by Todd Paris https://www.amandalindoo.com/permeability daily 0.75 2024-08-16 https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616698105648-PP4MZWUDVFG62QZODKP6/Fig7_2.png Permeability - Permeability development as a function of crystal-free melt viscosity. Prior to my research, the relative influence of melt viscosity versus crystal content on the percolation threshold was largely speculative. In Lindoo et al. (2016)*, I conducted decompression experiments on water-saturated rhyolite, rhyodacite, K-rich phonolite, and basaltic andesite melts. Following these experiments, I performed permeability and textural analyses on the quenched samples. My findings revealed that both silicic and mafic melts exhibit similar percolation thresholds (see figure), indicating that melt viscosity does not significantly impact the percolation threshold. However, melt viscosity does influence outgassing timescales by controlling the drainage and rupture of bubble films, which facilitates aperture formation. In silicic magmas, where bubble nucleation, growth, and coalescence are often delayed, the vesicularity necessary for permeability development may not be achieved until the magma reaches shallow depths. As a result, ascending rhyolite magmas may not outgas quickly enough to relieve overpressure at ascent rates of 10 m/s or greater, leading to explosive eruptions. In contrast, although mafic magmas also require high vesicularities before degassing occurs, bubble coalescence happens more readily, allowing for rapid outgassing. https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616697561767-CSJV3I360YSD4RMZ1VH0/Fig1A_color2.png Permeability - Crystal-controls on permeability development and degassing. Building on the finding that melt viscosity does not significantly control permeability development, I conducted another series of decompression experiments to investigate the effect of microlites on the percolation threshold. In Lindoo et al. (2017)*, I discovered that mafic magmas containing more than 20 vol.% microlites (white symbols, top figure) became permeable at a lower vesicularity (lower percolation threshold) compared to their crystal-free counterparts (black symbols) and silicic crystal-free melts (gray symbols). The presence of over 20 vol.% crystals significantly alters vesicle shapes and likely enhances vesicle connectivity, as illustrated by the binary images in the figure. This 20 vol.% crystal content corresponds to the critical volume fraction where prismatic crystals begin to interact—effectively a percolation threshold (bottom figure). At similar crystallinities, other studies have noted the onset of yield strength (hatched regions in the bottom figure), while the threshold for random loose packing (RLP) occurs at relatively higher particle fractions. The presence of crystals not only affects the bulk rheology of magma but also its degassing efficiency. Understanding these critical thresholds provides valuable insights into changes in eruption dynamics, thereby improving volcanic hazard assessment. https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616701327097-EA4NDLDHW5HWX5EE2IVW/Fig7_color.png Permeability - August 7-8 2008 eruption of Kasatochi Volcano. On August 7th and 8th, 2008, Kasatochi Volcano, an island stratovolcano located in the Central Aleutian Islands, erupted explosively and unexpectedly. The eruption comprised three major explosive events and two smaller events over the course of a single day, producing a bulk eruptive volume and ash cloud height consistent with a Volcanic Explosivity Index (VEI) of 4. The eruptive units contained juvenile clasts with a wide range of compositions and textures, spanning from basaltic andesite (52-56 wt.%) to andesite (58-62 wt.%), including some clasts with a banded mix of both endmembers (see figure). The textural and lithological diversity observed during this eruption provided a unique opportunity to correlate these characteristics with eruption dynamics. To better understand the coupled processes of crystallization and vesiculation during magma ascent, I quantitatively compared vesicle and crystal textures, permeabilities, and electrical tortuosities between the two endmember lithologies erupted from Kasatochi. This study was among the first to combine direct bulk measurements of connected vesicularity, permeability, and tortuosity with calculations of phenocryst and microlite crystallinities. The goal was to determine whether differences in magma composition and textural components influenced permeability development and degassing efficiency. https://www.amandalindoo.com/what daily 0.75 2024-08-16 https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616674410382-LEW1JF6PM1U9DC0KRFVN/cutaway.png What? https://www.amandalindoo.com/randp daily 0.75 2024-08-16 https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616678855718-H4T6WWL2WBTRTLG9Z21G/meltdist.png Melt residence and percolation - Core formation in small planetary bodies Meteorites offer a unique "window" into planetary interiors, providing valuable insights into the evolution of the early solar system and the processes of planetary differentiation. Iron meteorites, in particular, present an exceptional opportunity to study core formation processes. The diversity in chemical compositions observed among different iron meteorite groups suggests complex accretion and differentiation histories of their parent bodies. Understanding core-mantle segregation processes under various accretionary conditions can shed light on the range of chemical compositions recorded in meteorites. While planets may undergo different segregation processes depending on their heat sources and thermal evolution, differentiation through percolation is likely the dominant process in smaller planetary bodies when heated to temperatures sufficient to melt their metallic components. To explore this, I conducted piston-cylinder and multi-anvil experiments to investigate the percolation behavior of immiscible fluids in a multi-light element system. Specifically, I determined the chemical composition of immiscible liquids in the Fe-Ni-Si-S-C system and analyzed how temperature and pressure influence percolation behavior through texture analysis. https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616680491979-C8PLBJTSHCQCW7W0SMPV/Fig3_GPL.png Melt residence and percolation - Carbon mobility in subduction zones. The carbon flux between Earth's interior reservoirs remains a longstanding puzzle in geoscience. Carbonates, which make up a significant portion of subducting sediment, play a critical role in influencing arc volcanism and mantle carbon concentrations. Despite numerous experimental studies, the precise mechanisms governing how carbonates are recycled back into arc magmas or delivered to the mantle remain unclear. In my research, I conducted high-pressure, high-temperature multi-anvil experiments to investigate the wettability of a newly proposed amorphous phase of calcium carbonate within an olivine matrix. In porous matrices, fluids are typically transported through interconnected networks of pores along grain boundaries. The efficiency with which this amorphous phase percolates through such networks under subduction zone conditions depends on the solid-liquid dihedral angle of the system. My experiments revealed a thermally induced development of a melt-like fabric in the aggregate and a low dihedral angle, indicating that the amorphous phase should readily form an interconnected network, independent of melt volume. Due to its low density, amorphous CaCO₃ could buoyantly percolate into the overlying mantle wedge. [Image] Left column: BSE images of CaCO₃ in an olivine matrix. Right column: Ca maps showing the texture evolution of CaCO₃. https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616680764480-R9XSKSRW5QGIK3C8IN1V/Scape1.png Melt residence and percolation https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616756589335-99QOOOGVOTDS3BCJVWBG/HighPTalk_6719.png Melt residence and percolation https://www.amandalindoo.com/who daily 1.0 2024-08-16 https://www.amandalindoo.com/why daily 0.75 2024-08-16 https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616615530017-22RYNZDZYUVYUX554XCZ/unsplash-image-tLxGw_ITs7k.jpg Why? - How much melt is in the magma storage region? …and how much is eruptible? These are critical questions for volcanic hazard assessment. Seismology plays a key role in understanding the Earth's interior, forecasting volcanic eruptions, and characterizing magma reservoirs. Recent seismic experiments, supported by the GeoPRISMS and EarthScope Programs of the U.S. National Science Foundation, have yielded higher-resolution tomographic models of magma reservoirs, revealing previously unknown structures beneath volcanoes. Despite advancements in 3D seismic data acquisition and processing, quantitatively interpreting these data remains challenging. A major complication arises when attempting to translate modeled seismic velocity delays into actual melt percentages. This uncertainty can impact the accuracy of volcanic hazard assessments. To better constrain these estimates, it's essential to consider both compositional effects and the geometric distribution of melt within a porous matrix. https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616621920424-5E9RSXEMXX8BLJVIHNWQ/unsplash-image-I1MGVZ42wnU.jpg Why? - What causes transitions in eruption style? Transitions in the eruptive style of mafic magmas remain poorly understood. While silicic systems are more frequently researched and publicized due to their explosive nature, mafic volcanoes represent the most common form of volcanism on Earth. These volcanoes exhibit a wide range of eruption styles, typically characterized by effusive activity. However, changes in flow dynamics can lead to explosive, ash-generating episodes. The efficiency of volatile degassing from ascending magma plays a critical role in determining the eruptive style. Magma can degas through several mechanisms during ascent, including permeable wall rocks, viscous shear along conduit walls, or the formation of a permeable foam. Experimental methods allow us to constrain the threshold conditions that facilitate permeability development, providing insights into these complex processes. https://www.amandalindoo.com/rheology-of-magmas daily 0.75 2024-08-16 https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616754461161-YI3U04UO4H3VXAJ2814A/20210216_105629373_iOS.jpg High pressure-temperature rheology of magmas. https://images.squarespace-cdn.com/content/v1/6059e50a4d506c62e11721ea/1616754405302-6CSOEHAQA06RFUPRM4ZS/20200207_150837031_iOS.jpg High pressure-temperature rheology of magmas.