Continents are unique to Earth and played a role in coevolution of the atmosphere, hydrosphere, and biosphere. Debate exists, however, regarding continent formation and the onset of subduction-driven ...plate tectonics. We present Ca isotope and trace-element data from modern and ancient (4.0 to 2.8 Ga) granitoids and phase equilibrium models indicating that Ca isotope fractionations are dominantly controlled by geothermal gradients. The results require gradients of 500-750 °C/GPa, as found in modern (hot) subduction-zones and consistent with the operation of subduction throughout the Archaean. Two granitoids from the Nuvvuagittuq Supracrustal Belt, Canada, however, cannot be explained through magmatic processes. Their isotopic signatures were likely inherited from carbonate sediments. These samples (> 3.8 Ga) predate the oldest known carbonates preserved in the rock record and confirm that carbonate precipitation in Eoarchaean oceans provided an important sink for atmospheric CO
. Our results suggest that subduction-driven plate tectonic processes started prior to ~3.8 Ga.
Earth has had a global magnetic field for at least 3.5 billion years, but if the iron-alloy in the core has high conductivity, it is difficult to explain this duration with energy from cooling and ...inner-core growth alone. Precipitation of light elements (e.g., magnesium, silicon, and oxygen) from Earth's core is a potential alternative energy source to power the dynamo. We develop a new framework of coupled thermo-chemical evolution of the Earth to consider precipitation of multiple light components from the core and their interaction with the overlying mantle layer. The precipitated material accumulates in a layer at the base of the mantle which is then continuously eroded by mantle convection. We allow the precipitation of three species (MgO, FeO, and SiO2), including their interactions not considered by most previous studies. We find that MgO, SiO2, and FeO precipitation may each dominate entropy production depending on the choice of equilibrium constants and initial model states and that the three species together can explain the duration of Earth's magnetic field across a range of plausible scenarios. Over the Earth's history, we find that the core can lose ∼1–2 wt% silicon and oxygen suggesting that light precipitation is potentially an important process for the core compositional evolution and core-mantle chemical exchange. Additionally, our results show that precipitation does not, in most cases, have a systematic influence on the timing of inner-core nucleation or magnitude of the resulting paleomagnetic signal with inner-core nucleation typically around 550 Mya. However, the onset of precipitation of individual species could produce additional sharp increases in paleomagnetic intensity at various points through Earth's history besides the inner-core nucleation event.
•Coupled chemical thermodynamic framework for thermo-chemical Earth's core evolution.•A significant impact of mantle interaction layer dynamics on precipitation rate.•Coupled Precipitation of MgO, SiO2, and FeO provides sufficient entropy.
On the 7 August 2019, a 195 km2 raft of andesitic pumice was produced at 200 m below sea level at an unnamed submarine volcano in the Tonga Islands (Southwest Pacific Ocean). Drifting chiefly ...westward, the raft reached the Fiji Islands on the 19 September. Yachts that crossed the raft as early as 2 days post‐eruption provided an outstanding data set of raft characteristics and pristine samples. Further, exceptional tracking of raft dispersal by satellite images allows us to contrast virtual particle tracking methods with ocean model currents to explore the relative influence of surface currents, wind, and wave action on pumice flotsam dispersal over up to 2 years. Attenuation of ocean waves by large and compact pumice rafts appears to reduce the effect of Stokes drift. The coupling of real‐time satellite observations with oceanographic Lagrangian simulations allows near‐real time forecasting for global maritime hazard mitigation.
Plain Language Summary
Although 70% of volcanism occurs underwater, submarine eruptions are seldom witnessed owing to their remoteness and absence of technologies enabling their detection. On the 7 August 2019, a submarine volcanic eruption 200 m below sea level in the Tonga Islands formed a 195 km2 pumice raft. The raft was first encountered and sampled by yacht crews, and is visible on satellite images. Pumice rafts are dispersed by ocean currents, wind, and waves, and can cross entire oceans or get stranded on coasts. After 7 weeks of dispersal, the pumice raft reached the Fiji Islands, and a fraction continued its westward route toward Vanuatu and eastern Australia. Excellent imaging of the raft by satellites permitted reconstruction of daily raft dispersal for the first 8 weeks. Here we show that drift calculations, including components of ocean current, wind, and wave action, can usefully forecast raft dispersal. We tested and tuned these drift calculations by comparing the simulated drift with daily satellite images of the raft. Further, a combination of satellite images and drift calculations based on oceanographic models were used for maritime hazard mitigation in near‐real time.
Key Points
A >30 million m3 pumice raft formed at an unnamed volcano in Tonga midday on the 7 August 2019 and was dispersed by ocean currents and wind
Forecasts of pumice raft dispersal, based on particle drift with model currents, winds, and waves, are evaluated with daily satellite images
Stokes drift does not improve short‐term predictions on large and compact pumice rafts because these rafts attenuate ocean waves
Constraining the eruption rates of flood basalt lava flows remains a significant challenge despite decades of work. One potential observable proxy for eruption rates is flood basalt lava-flow lobe ...thicknesses, a topic that we tackle here quantitatively. In this study, we provide the first global compilation of pāhoehoe lava-lobe thicknesses from various continental flood basalt provinces (∼ 3,800 measurements) to compare characteristic thicknesses within and between provinces. We refer to thin lobes (∼ ≤5 m), characteristic of “compound” lavas, as hummocky pāhoehoe lava flows or flow-fields. Conversely, we term thicker lobes, characteristic of “simple” flows, as coming from sheet-lobe-dominated flows. Data from the Deccan Traps and Columbia River flood-basalt provinces are archetypal since they have the most consistent datasets as well as established chemo- and litho-stratigraphies. Examining Deccan lobe thicknesses, we find that previously suggested (and disputed) distinct temporal and regional distributions of hummocky pāhoehoe and sheet-lobe-dominated flow fields are not strongly supported by the data and that each geochemically defined formation displays both lobe types in varying amounts. Thin flow-lobes do not appear to indicate proximity to source. The modal lobe thickness of Deccan formations with abundant “thin” lava-lobes is 8 m, while the mode for sheet-lobe-dominated formations is only 17 m. Sheet-lobes up to 75–80 m are rare in the Deccan and Columbia River Provinces, and ones >100 m are exceptional globally. For other flood basalt provinces, modal thickness plots show a prevalence toward similar lobe thicknesses to Deccan, with many provinces having some or most lobes in the 5–8 m modal range. However, median values are generally thicker, in the 8–12 m range, suggesting that sheet-lobes dominate. By contrast, lobes from non-flood basalt flow-fields (e.g., Hawai’i, Snake River Plain) show distinctly thinner modes, sub-5 m. Our results provide a quantitative basis to ascertain variations in gross lava morphology and, perhaps, this will in future be related to emplacement dynamics of different flood basalt provinces, or parts thereof. We can also systematically distinguish outlier lobes (or regions) from typical lobes in a province, e.g., North American Central Atlantic Magmatic Province lava-lobes are anomalously thick and are closely related to feeder-intrusions, thus enabling a better understanding of conditions required to produce large-volume, thick, flood basalt lava-lobes and flows.
The interaction of mantle plume driven flow with upwelling flow due to a nearby mid‐ocean ridge occurs for many mantle plumes including Galápagos and Iceland. This interaction is typified by trace ...element and isotopic signatures demonstrating the “contamination” of normal ridge composition by relatively enriched plume material. However, another common signature of plume‐ridge interaction is volcanic lineaments linking ridges and nearby plumes, perhaps most conspicuously the Wolf‐Darwin lineament (WDL) at Galápagos and the Rodrigues Ridge (RR) at La Réunion. These enigmatic features remain unexplained. Plume‐ridge interaction is commonly modeled in terms of interaction between solid‐state plume flow and divergent ridge flow, but such models do not likely lead to the kind of solid‐state flow channelization that might explain narrow features such as the WDL and RR. Likewise, models involving tapping of anomalously hot and/or fertile asthenosphere between the plume and ridge due to lithospheric faulting appear to be inconsistent with a variety of evidence. We propose an alternative model in which the lineaments are the surface expressions of localized melt channels in the asthenosphere formed due to instabilities in a two‐phase partially molten system. A thermodynamic analysis shows that given the magma fluxes inferred to be associated with structures such as WDL and RR, these melt channels can be maintained over plume‐ridge distances up to ∼1000 km. These results suggest that plume‐ridge interaction in general, possibly including transport of plume‐derived material along ridge axes (e.g., Iceland), may involve transport in high‐melt‐fraction channels, as opposed to just solid‐state mantle flow.
Key Points
Geophysical observations suggest that solid‐state mantle flow or lithospheric faulting models do not describe certain volcanic lineaments
We propose a new model based on channelized transport of plume melt to the ridge—lineaments are the surface expressions of melt channels
Plume‐ridge interaction may occur on two distinct scales—a larger solid‐state transport and a smaller channelized melt transport scale
We analyse two representative rubbly pāhoehoe lavas (F3 and F5) from drill cores at Tural-Rajwadi, southwest of Koyna, in the southern Deccan Traps. Low vesicle deformation (0.1 to 0.4) indicates ...that both lavas ultimately cooled under a low-stress regime. The crystal size distributions (CSDs) of most samples from F5 (especially those from within the core) are not linear but instead show kinks. These kinks are attributed to a rise in plagioclase nucleation due to degassing following the brecciation of the crust. Since it is difficult to constrain cooling time for ancient lava flows, we used the products of nucleation rates (Jt, 1.64 × 10
–8
to 1.45 × 10
–5
μm
−3
) and growth rates (Gt, 2.1 to 156 μm) with time. When compared with natural analogues as well as experimental results for basalt crystallisation, these values suggest a much faster lava cooling rate (~ 1 to 7℃/hr) than a conductive cooling model (≤ 0.1 ℃/hr). The CSDs for F3 fan with depth suggesting that the lava flow might represent local accumulation (ponding?) in a transitional lava flow field. CSDs for F5 show little variation with depth, with the exception of kinks for samples from the lower crust and core. The relatively higher number density of plagioclase microcrysts in our rubbly pāhoehoe (F5) and their CSD patterns are similar to those measured for transitional lavas from Hawaii. The vesicle data and CSDs indicate that brittle deformation was the primary mode of transition within these lavas. Identifying occurrence of thick ponded lavas within vertical stacks of rubbly pāhoehoe flows in the upper stratigraphic levels of the Deccan Traps are critically important as they demonstrate complex cooling styles, crystallisation histories, and emplacement dynamics. Transitional lavas such as rubbly pāhoehoe are important components of large CFB provinces such as the Deccan Traps and constitute nearly 46 to 85% of all lava types. Modelling of continental flood basalt provinces should therefore account for these diversities within lavas, and any oversimplified version using end-member morphotypes is unrealistic and untenable.
Volcanoes that deposit eruptive products into the ocean can trigger phytoplankton blooms near the deposition area. Phytoplankton blooms impact the global carbon cycle, but the specific conditions and ...mechanisms that facilitate volcanically triggered blooms are not well understood, especially in low nutrient ocean regions. We use satellite remote sensing to analyze the chlorophyll response to an 8‐month period of explosive and effusive activity from Nishinoshima volcano, Japan. Nishinoshima is an ocean island volcano in a low nutrient low chlorophyll region of the Northern Pacific Ocean. From June to August 2020, during explosive activity, satellite‐derived chlorophyll‐a was detectable with amplitudes significantly above the long‐term climatological value. After the explosive activity ceased in mid‐August 2020, these areas of heightened chlorophyll concentration decreased as well. In addition, we used aerial observations and satellite imagery to demonstrate a spatial correlation between blooms and ash plume direction. Using a sun‐induced chlorophyll‐a fluorescence satellite product, we confirmed that the observed chlorophyll blooms are phytoplankton blooms. Based on an understanding of the nutrients needed to supply blooms, we hypothesize that blooms of nitrogen‐fixing phytoplankton led to a 1010–1012 g drawdown of carbon. Thus, the bloom could have significantly mediated the output of carbon from the explosive phase of the eruption but is a small fraction of anthropogenic CO2 stored in the ocean or the global biological pump. Overall, we provide a case study of fertilization of a nutrient‐poor ocean with volcanic ash and demonstrate a scenario where multi‐month scale deposition triggers continuous phytoplankton blooms across 1,000s of km2.
Plain Language Summary
Volcanic eruptions can cause organisms known as phytoplankton to multiply and form what is known as a phytoplankton bloom in the ocean. Phytoplankton blooms can impact the life cycle of carbon in the earth system, but it is not always obvious why phytoplankton blooms happen. Using different satellite data, we observe phytoplankton blooms by viewing chlorophyll concentration in the ocean. Nishinoshima is a remote volcano in an area of the Pacific that lacks nutrients necessary for phytoplankton blooms. Nishinoshima erupted in 2019–2020 and deposited lava and ash into the ocean at different times. By looking at the chlorophyll concentration during the time periods lava and ash were deposited into the ocean, we found that chlorophyll concentration increased when ash was deposited into the ocean. These increases in chlorophyll concentration were determined to be phytoplankton blooms. These phytoplankton blooms may utilize nutrients from volcanic ash and the atmosphere, leading to a drawdown of atmospheric carbon.
Key Points
Ash deposition triggers phytoplankton blooms at Nishinoshima during the explosive phase of the 2019–2020 eruption
Phytoplankton blooms were not present during the effusive phase of the 2019–2020 eruption
Phytoplankton blooms triggered by ash deposition can lead to carbon drawdown that can mediate the carbon output from the eruption
Abstract
The 15 January 2022 eruption of Hunga Tonga-Hunga Ha’apai, and the preceding eruptions on 19 December 2021 and 13 January 2022, were remarkable, partly because the eruptions generated ...extensive umbrella clouds, regions where the volcanic clouds spread laterally. Here we use satellite remote sensing to evaluate the umbrella cloud tops’ heights, longevities, water contents, and volumetric flow rates. We identified two umbrella clouds at distinct elevations on 15 January 2022. Specifically, after 05:30 UTC, the strong westward propagation of an upper umbrella cloud at 31 km ± 3 km enabled the visibility of the lower umbrella cloud at 17 km ± 2 km. The satellite-derived volumetric flow rate for 15 January 2022 was ~5.0 × 10
11
m
3
s
−1
, nearly two orders of magnitude higher than the volumetric flow rates estimated for the 19 December 2021 and 13 January 2022 eruptions. Finally, we found that the umbrellas on all three dates were ice-rich.
Deccan Traps flood basalt volcanism affected ecosystems spanning the end‐Cretaceous mass extinction, with the most significant environmental effects hypothesized to be a consequence of the largest ...eruptions. The Rajahmundry Traps are the farthest exposures (~1,000 km) of Deccan basalt from the putative eruptive centers in the Western Ghats and hence represent some of the largest volume Deccan eruptions. Although the three subaerial Rajahmundry lava flows have been geochemically correlated to the Wai Subgroup of the Deccan Traps, poor precision associated with previous radioisotopic age constraints has prevented detailed comparison with potential climate effects. In this study, we use new 40Ar/39Ar dates, paleomagnetic and volcanological analyses, and biostratigraphic constraints for the Rajahmundry lava flows to ascertain the timing and style of their emplacement. We find that the lower and middle flows (65.92 ± 0.25 and 65.67 ± 0.08 Ma, ±1σ systematic uncertainty) were erupted within magnetochron C29r and were a part of the Ambenali Formation of the Deccan Traps. By contrast, the uppermost flow (65.27 ± 0.08 Ma) was erupted in C29n as part of the Mahabaleshwar Formation. Given these age constraints, the Rajahmundry flows were not involved in the end‐Cretaceous extinction as previously hypothesized. To determine whether the emplacement of the Rajahmundry flows could have affected global climate, we estimated their eruptive CO2 release and corresponding climate change using scalings from the LOSCAR carbon cycle model. We find that the eruptive gas emissions of these flows were insufficient to directly cause multi‐degree warming; hence, a causal relationship with significant climate warming requires additional Earth system feedbacks.
Plain Language Summary
Flood basalt eruptions are among the largest volcanic eruptions in Earth's history and are frequently associated with mass extinctions. The Deccan Traps flood basalt erupted close in time to the end‐Cretaceous mass extinction, which marked the demise of the dinosaurs. We determine the timing of the largest known Deccan eruptions, the Rajahmundry Traps, which are potentially the longest lava flows in the world. These eruptions were thought to have played a role in the mass extinction. We estimate when these eruptions happened using techniques including 40Ar/39Ar radioisotopic dating, paleomagnetism, micropaleontology, and geochemistry. We find that the Rajahmundry Traps erupted after the mass extinction. Additionally, we find that the eruptions happened around the same time interval as climate warming which may have impacted the ecological recovery after the mass extinction. We model the climate effects of the Rajahmundry eruptions and find that their eruptive CO2 emissions were likely not enough to directly cause multi‐degree warming. However, volcanic systems may non‐eruptively emit CO2 or may cause other environmental effects which could indirectly increase the amount of climate warming.
Key Points
Exposed Rajahmundry Traps lava flows were all erupted after the Cretaceous‐Paleogene boundary, between 65.92 and 65.27 million years ago
Rajahmundry Traps consistent with Deccan Traps chronostratigraphy and chemostratigraphy thus are very long flows from main Deccan eruptive vents
Model and climate records show that eruptive CO2 release from large individual Deccan eruptions is insufficient to cause significant warming
Its extraordinary level of geologic activity, its potential for habitability, and the prospects of returning samples from its plume of erupting water ice make Saturn's small (∼500 km diameter) moon ...Enceladus a high priority target for future exploration and a key to our developing understanding of icy ocean worlds. The structure of its outer ice shell is particularly important as it relates to the global heat budget, the global-scale response to tidal forces, and the nature of the ongoing eruptions. It is also diagnostic of how and where heat is dissipated internally. Here, using the most recent shape model and a new approach to modeling isostasy, we obtain a shell structure that simultaneously accommodates the shape, gravity, and libration observations and suggests that tidal dissipation near the base of the ice shell is likely an important mode of internal heating. The implied conductive heat loss is greater than the heat loss associated with the eruptions but is nevertheless compatible with the condition of steady state.
•We use new data and theory to constrain the structure of Enceladus's ice shell.•The inferred shell structure matches expectations from a tidal heating model.•Tidal dissipation within the ice shell is likely an important mode of internal heating.
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