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1. Fizzy Super-Earths: Impacts of Magma Composition on the Bulk Density and Structure of Lava Worlds

   https://doi.org/10.3847/1538-4357/acea85  

   Boley, Kiersten M.; Panero, Wendy R.; Unterborn, Cayman T.; Schulze, Joseph G.; Martínez, Romy Rodríguez; Wang 王, Ji 吉 (September 2023, The Astrophysical Journal)

   Abstract Lava worlds are a potential emerging population of Super-Earths that are on close-in orbits around their host stars, with likely partially molten mantles. To date, few studies have addressed the impact of magma on the observed properties of a planet. At ambient conditions, magma is less dense than solid rock; however, it is also more compressible with increasing pressure. Therefore, it is unclear how large-scale magma oceans affect planet observables, such as bulk density. We updateExoPlex, a thermodynamically self-consistent planet interior software, to include anhydrous, hydrous (2.2 wt% H₂O), and carbonated magmas (5.2 wt% CO₂). We find that Earth-like planets with magma oceans larger than ∼1.5R_⊕and ∼3.2M_⊕are modestly denser than an equivalent-mass solid planet. From our model, three classes of mantle structures emerge for magma ocean planets: (1) a mantle magma ocean, (2) a surface magma ocean, and (3) one consisting of a surface magma ocean, a solid rock layer, and a basal magma ocean. The class of planets in which a basal magma ocean is present may sequester dissolved volatiles on billion-year timescales, in which a 4M_⊕mass planet can trap more than 130 times the mass of water than in Earth’s present-day oceans and 1000 times the carbon in the Earth’s surface and crust. 

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2. Atmosphere-interior Exchange on Hot, Rocky Exoplanets

   https://doi.org/10.3847/0004-637X/828/2/80  

   Kite, Edwin S.; Fegley, Bruce; Schaefer, Laura; Gaidos, Eric (September 2016, Astrophysical journal)

   We provide estimates of atmospheric pressure and surface composition on short-period, rocky exoplanets with dayside magma pools and silicate-vapor atmospheres. Atmospheric pressure tends toward vapor-pressure equilibrium with surface magma, and magma-surface composition is set by the competing effects of fractional vaporization and surface-interior exchange. We use basic models to show how surface-interior exchange is controlled by the planet’s temperature, mass, and initial composition. We assume that mantle rock undergoes bulk melting to form the magma pool, and that winds flow radially away from the substellar point. With these assumptions, we find that: (1) atmosphere-interior exchange is fast when the planet’s bulk-silicate FeO concentration is low, and slow when the planet’s bulk-silicate FeO concentration is high; (2) magma pools are compositionally well mixed for substellar temperatures ≲2400 K, but compositionally variegated and rapidly variable for substellar temperatures ≳2400 K; (3) currents within the magma pool tend to cool the top of the solid mantle (“tectonic refrigeration”) (4) contrary to earlier work, many magma planets have time-variable surface compositions. 

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3. The Prevalence and Significance of Offset Magma Reservoirs at Arc Volcanoes

   https://doi.org/10.1029/2020GL087856  

   Lerner, Allan H.; O'Hara, Daniel; Karlstrom, Leif; Ebmeier, Susanna K.; Anderson, Kyle R.; Hurwitz, Shaul (July 2020, Geophysical Research Letters)

   Abstract Determining the spatial relations between volcanic edifices and their underlying magma storage zones is fundamental for characterizing long‐term evolution and short‐term unrest. We compile centroid locations of upper crustal magma reservoirs at 56 arc volcanoes inferred from seismic, magnetotelluric, and geodetic studies. We show that magma reservoirs are often horizontally offset from their associated volcanic edifices by multiple kilometers, and the degree of offset broadly scales with reservoir depth. Approximately 20% of inferred magma reservoir centroids occur outside of the overlying volcano's mean radius. Furthermore, reservoir offset is inversely correlated with edifice size. Taking edifice volume as a proxy for long‐term magmatic flux, we suggest that high flux or prolonged magmatism leads to more centralized magma storage beneath arc volcanoes by overprinting upper crustal heterogeneities that would otherwise affect magma ascent. Edifice volumes therefore reflect the spatial distribution of underlying magma storage, which could help guide monitoring strategies at volcanoes. 

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4. Modeling the Intermittent Lava Lake Drops Occurring Between 2015 and 2021 at Nyiragongo Volcano

   https://doi.org/10.1029/2022GL102365  

   Walwer, D.; Wauthier, C.; Barrière, J.; Smittarello, D.; Smets, B.; d’Oreye, N. (April 2023, Geophysical Research Letters)

   Abstract Between 2015 and 2021, Nyiragongo's lava lake level experienced a linear increase punctuated by fast intermittent drops. These drops occurred synchronously to seismic swarm at approximately 15 km below the surface and extending laterally NE from the volcano. To interpret these lava lake level patterns in terms of reservoirs pressure evolution within Nyiragongo, we consider the following simplified plumbing system: a central reservoir is fed by a constant flux of magma, distributing the fluid up into the lava lake and laterally into a distal storage zone. Magma transport is driven by a pressure gradient between the magma storage bodies, accommodating influx and outflow of magma elastically, and the lava lake. Lateral transport at depth occurs through a hydraulic connection for which the flow resistance is coupled to the magma flux. When the right conditions are met, lateral magma transport occurs intermittently and triggers intermittent lava lake level drops matching the observations. 

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5. Feasibility of melt segregation from a crystal mush in response to the 2011–2012 eruption at Cordón Caulle, Chile

   https://doi.org/10.1093/gji/ggad259  

   Phelps, Patrick_R; Gonnermann, Helge_M; Winslow, Heather; Ruprecht, Philipp; Pritchard, Matthew_E; Delgado, Francisco; Liao, Yang (June 2023, Geophysical Journal International)

   SUMMARY The 2011–2012 eruption at Cordón Caulle in Chile produced crystal-poor rhyolitic magma with crystal-rich mafic enclaves whose interstitial glass is of identical composition to the host rhyolite. Eruptible rhyolites are thought to be genetically associated with crystal-rich magma mushes, and the enclaves within the Cordón Caulle rhyolite support the existence of a magma mush from which the erupted magma was derived. Moreover, towards the end of the 2011–2012 eruption, subsidence gave way to inflation that has on average been continuous through at least 2020. We hypothesize that magma segregation from a crystal mush could be the source of the observed inflation. Conceptually, magma withdrawal from a crystal-poor rhyolite reservoir caused its depressurization, which could have led to upward flow of interstitial melt within an underlying crystal mush, causing a new batch of magma to segregate and partially recharge the crystal-poor rhyolite body. Because the compressibility of the crystalline matrix of the mush is expected to be lower than that of the interstitial melt, which likely contains some fraction of volatile bubbles, this redistribution of melt would result in a net increase in volume of the system and in the observed inflation. We use numerical modelling of subsurface magma flow and storage to show under which conditions such a scenario is supported by geodetic and petrologic observations. 

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