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• Trees are known to emit methane (CH₄) and nitrous oxide (N₂O), with tropical wetland trees being considerable CH₄ sources. Little is known about CH₄ and especially N₂O exchange of trees growing in tropical rain forests under nonflooded conditions. • We determined CH₄ and N₂O exchange of stems of six dominant tree species, cryptogamic stem covers, soils and volcanic surfaces at the start of the rainy season in a 400-yr-old tropical lowland rain forest situated on a basaltic lava flow (Réunion Island). We aimed to understand the unknown role in greenhouse gas fluxes of these atypical tropical rain forests on basaltic lava flows. • The stems studied were net sinks for atmospheric CH₄ and N₂O, as were cryptogams, which seemed to be co-responsible for the stem uptake. In contrast with more commonly studied rain forests, the soil and previously unexplored volcanic surfaces consumed CH₄. Their N₂O fluxes were negligible. • Greenhouse gas uptake potential by trees and cryptogams constitutes a novel and unique finding, thus showing that plants can serve not only as emitters, but also as consumers of CH₄ and N₂O. The volcanic tropical lowland rain forest appears to be an important CH₄ sink, as well as a possible N₂O sink.

The main parameters required to forecast lava flows are the eruption effusion rate, the lava viscosity, and the pre‐eruption topography. We focus on how the spatiotemporal resolution and vertical errors of topographic measurements affect lava flow forecasts. We develop a basic fluid mechanical flow model that, combined with theory, allows us to study the propagation of lava flows on simple noisy topography. We find that topographic noise acts to retard and widen the flow and show that relative noise greater than approximately 10% of the flow thickness significantly reduces the simulated advance rates and compromises the retrieval of the other eruption parameters. We also analyze how vertical topographic error, spatial sampling, and the time sampling frequency affect the effusion rate uncertainty. This work provides a basis for understanding how repeat topography data sampling and precision can affect forecasting lava flow spatiotemporal inundation and inform observation needs from future topography missions.

Dating young lava flows is essential for understanding volcano's eruption frequency, yet challenging due to methodological limitations of commonly used dating techniques. Ruapehu (Aotearoa New Zealand) produced many lava flows during the Holocene, but constraints on the timing of these eruptions are scarce. Here, we use paleomagnetic dating to deliver new eruption ages of 18 lava flows with uncertainties ranging between 500 and 2,700 years (at the 95% confidence level). Comparison between lava flows' paleomagnetic directions and a local paleosecular variation record indicates that the large lava flow field located on the Whakapapa area was emplaced during at least three distinct eruptive episodes between 10600 and 7400 BP. Two of these episodes closely followed a large collapse event that affected Ruapehu's northern area and generated large volumes of lava between 10600 and 8800 BP, with the third episode producing less voluminous lava flows between 8100 and 7400 BP. Following a smaller collapse of the southeastern sector of the edifice at ca. 5300 BP, several low‐volume lava flows were emplaced during at least two distinct eruptive episodes prior to ca. 1000 BP, which supplied the Whangaehu valley with lava. The youngest age inferred from our data represents the youngest eruption age provided for a lava flow outside Ruapehu's summit region. This research provides greater detail to the Holocene effusive chronology at Ruapehu, shedding light on partial cone reconstructions after edifice collapses during the Holocene, and the time relationships between trends observed in its effusive and explosive activity. Plain Language Summary Knowing when volcanoes have erupted is essential for hazard assessments, but the precise timing of geologically young lava flow eruptions is hard to determine with traditional methods. Earth's magnetic field is constantly changing in both direction and strength. Magnetic minerals contained in the lava flows record the direction of the field as the lava cools after eruption. Hence, solidified lavas can be dated by matching their magnetization directions to a reference record. In this study, we analyze the magnetization directions recorded in prehistoric lavas at Mt. Ruapehu (Aotearoa New Zealand) and use them to determine when they erupted. We show that a large flow field in the Whakapapa area (northwest Ruapehu) was formed during at least three distinct eruptive episodes between 10,600 and 7,350 years ago, following a catastrophic volcanic landslide at around 10,600 years ago. We also determine that the lavas present in the Whangaehu valley (east Ruapehu) erupted during at least two episodes between 4,600 and 1,000 years ago, the latter representing the youngest lavas known outside the summit area of Ruapehu. This research helps understand how Ruapehu was rebuilt after slope collapses, and the frequency of lava‐forming eruptions. Key Points Paleomagnetism was used to date eruptive episodes in lava flow sequences at Ruapehu Paleomagnetic dating yields 1300–1050 BP as the youngest eruption age known for a lava flow at the volcano Our data provide age constraints on the timescales of vent migration and partial edifice rebuilding after collapse events

The 2021 Tajogaite eruption of Cumbre Vieja (La Palma, Spain) was typified by the emission of low viscosity lavas that flowed at high velocities and inundated a large area. We experimentally investigated the rheological evolution of melt feeding the eruption through concentric cylinder viscometry to understand the exceptional flowing ability of these lavas and constrain its emplacement dynamics. We conducted a set of cooling deformation experiments at different cooling rates (from 0.1 to 10 °C/min), and isothermal deformation experiments at subliquidus dwell temperatures between 1225 and 1175°C. All experiments were conducted at a shear rate of 10 s−1. Results show that disequilibrium crystallization and its timescale fundamentally control the rheological evolution of the melt, resulting in different rheological response to deformation of the crystal‐bearing magmatic suspension. Integrating rheological data with field observations allows us to shed light on the mechanisms that govern the high flowability of these lavas. Plain Language Summary Understanding and modeling the mechanisms controlling the inundation ability of lava flows is pivotal for hazard assessment and mitigation of related risk. Lavas flowing across the Earth's surface experience different cooling conditions. These conditions are related to the thermal gradients generated at various levels within the flow's thickness. Especially for extremely fluid magmas such as those erupted at Cumbre Vieja, the different cooling paths (and different disequilibrium conditions) that lava flows experience strongly influence the crystallization processes. Both cooling and crystallization produce an increase of lava viscosity, hindering lava flowability. If crystallization occurs over timescales shorter than those of cooling, the presence of crystals may give rise to more complex flow behavior and emplacement style, including flow rupture and separation. Such conditions may favor the development of flow decoupling and lava tunnel formation. In this study we experimentally investigate the viscosity evolution of the Tajogaite lavas and the transition from pure viscous flow to more complex responses to deformation. Then, we use our data set in concert with field observation to constrain the dynamics governing the emplacement style of these lavas. Key Points High‐T deformation experiments characterize the rheology of Cumbre Vieja lavas under both disequilibrium and equilibrium conditions Two different rheological responses are observed in relation to the increased disequilibrium conditions at which the melt is subjected Integration of experimental and field data permits to understand the mechanisms that enhance the flowing ability of these lavas

The 1730–1736 eruption on Lanzarote was one of the most significant volcanic eruptions to occur on the Canary Islands, with lavas covering over 200 km2. Globally, it is volumetrically the third largest known subaerial basaltic fissure eruption in the past 1,100 years. Here we use Sentinel‐1 and ENVISAT interferograms on both ascending and descending orbits to construct a time series of line‐of‐sight surface displacements and calculate linear vertical deformation rates. We resolve a constant subsidence rate of about 6 mm/yr associated with an area of ∼20 km2 within the central and western portion of the Timanfaya lava flows relative to the rest of the island. This is consistent over the 28‐year period (1992–2020) covered by the Sentinel‐1 and ENVISAT data when combined with the previously published European Remote‐Sensing Satellite data. Time series constructed using Sentinel‐1 short interval interferograms have previously been shown to suffer systematic biases and we find that by making longer period interferograms these biases can be mitigated (when compared against an averaged stack of 1‐year interferograms). Cooling‐driven contraction of an intrusion would require improbably large sill thickness to achieve the observed subsidence rates. Our observations are consistent with the cooling of lavas on the order of one hundred meters, twice as thick as previous estimates, which suggests overall lava volume for this eruption may have been underestimated. This is also evidence of the longest duration of lava flow subsidence ever imaged which indicates that these cumulative thick flows can continue to deform significantly even three centuries after emplacement. Plain Language Summary A common result of a sustained volcanic eruption is large outpourings of lavas that can form thick flows when activity lasts many years. One of the ways to measure the behavior of active volcanoes is to use satellites to observe how fast parts of the volcano surface are moving. It is important to be able to estimate the different physical processes that may lead to the surface deformation around a volcano. One of these processes is the contraction of thick lava flows which rapidly subside due to cooling. Here we use radar satellites to measure how fast parts of Lanzarote are sinking. We find that despite these lava flows being nearly three centuries old, they are still sinking at about half a centimeter every year. These are the oldest flows known to still be measurably subsiding. This shows that when multiple stacked lava flows get very thick (here estimated at over 100 m in thickness), they are still able to continue deforming centuries later. It is important to know this is due to lava subsidence as other magmatic processes can also lead to subsidence and these might be of greater hazard concern and could indicate the subsurface migration of magma. Key Points We detect multi‐decade subsidence of up to 6 mm/yr across Timanfaya lavas emplaced almost 300 years ago using Interferometric Synthetic Aperture Radar time series Peak subsidence is consistent with the cooling of 100–150 m thick lava flows We demonstrate mitigation of time series bias from short‐period interferograms in Sentinel‐1 by using longer networks

When a lava flow enters a body of water, either a lake, sea, river or ocean, explosive interaction may arise. However, when it is an 'a'ā lava flow entering water, a more complex interaction occurs, that is very poorly described and documented in literature. In this paper, we analysed the 2–4 ka San Bartolo lava flow field emplaced on the north flank of Stromboli volcano, Italy. The lava flow field extends from ~ 650 m a.s.l. where the eruptive fissure is located, with two lava channels being apparent on the steep down to the coast. Along the coast the lava flow field expands to form a lava delta ~ 1 km wide characterised by 16 lava ‘Flow’ units. We performed a field survey to characterise the features of lava entering the sea and the associated formation of different components and magnetic measurements to infer the flow fabrics and emplacement process of the lava flow system. We measured the density, porosity and connectivity of several specimens to analyse the effect of lava-water interaction on the content in vesicles and their connectivity and conducted a macroscopic componentry analysis (clast count) at selected sites to infer the character of the eroded offshore segment of the lava flow field and its component flow units. The collected data allowed us to define the main components of a lava delta fed by 'a'ā lava flows, with its channels, littoral units, ramps, lava tubes, and inflated pāhoehoe flows controlled by the arterial 'a'ā flow fronts. The spatial organisation of these components allowed us to build a three-step descriptive model for 'a'ā entering a water. The initial stage corresponds to the entry of channel-fed 'a'ā lava flow into the sea which fragments to form metric blocks of 'a'ā lava. Continued lava supply to the foreshore causes flow units to stall while spreading over this substrate. Subsequent 'a'ā lava flow units ramp up behind the stalled flow front barrier. Lava tubes extending through the stalled flow barrier feed the seaward extension of a bench made of several pāhoehoe flow units.

The simultaneous or sequential occurrence of several hazards—be they of natural or anthropogenic sources—can interact to produce unexpected compound hazards and impacts. Since success in responding to volcanic crises is often conditional on accurate identification of spatiotemporal patterns of hazard prior to an eruption, ignoring these interactions can lead to a misrepresentation or misinterpretation of the risk and, during emergencies, ineffective management priorities. The 2021 eruption of Tajogaite volcano on the island of La Palma, Canary Islands (Spain), was an 86 day-long hybrid explosive-effusive eruption that demonstrated the challenges of managing volcanic crises associated with the simultaneous emission of lava, tephra and volcanic gases. Here, we present the result of a small-scale impact assessment conducted during three-field deployments to investigate how tephra fallout and lava flow inundation interacted to cause compound physical impact on buildings. The study area was a neighbourhood of 30 buildings exposed to tephra fallout during the entire eruption and by a late-stage, short-lived lava flow. Observations highlight, on one hand, the influence of clean-up operations and rainfall on the impact of tephra fallout and, on the other hand, the importance of the dynamics of lava flow emplacement in controlling impact mechanisms. Overall, results provide an evidence-based insight into impact sequences when two primary hazards are produced simultaneously and demonstrate the importance of considering this aspect when implementing risk mitigation strategies for future long-lasting, hybrid explosive-effusive eruptions in urban environments.

The 20th century eruptions of the Santorini volcano in Greece are the most recent activity of the volcano’s long lifespan. While the different eruptions taking place between 1925 and 1950 have traditionally been considered to exhibit similar eruptive styles, aspects of their evolution and precise information related to the individual eruption dynamics were poorly constrained. This study collates field reports and historical accounts, mainly from the Greek national scientific committee, which was assigned to study the volcanic activity in Nea Kameni Island with recent field campaigns. This analysis provides further insight into these eruptions and attempts to unravel the timing and style of explosive and effusive episodes that took place. Reconstruction of the recent geological evolution and of the eruptive history allow a more complete description of the eruption dynamics and associated unrest. These include fumarolic behaviour, explosion intensity, direction and volume of the lava flows, eruption duration, vent morphological changes (such as craters, domes, and horseshoe ramparts), textural characteristics and lava morphologies, as well as surface fracturing. Specific features related to first-hand accounts of the eruptions and associated products, in conjunction with our in situ post-eruptive geological study, allow an improved reconstruction of activity, both prior to and during the historical eruptions, which contributes to understanding the development of the eruption and enhances the forecast of potential future eruptions from patterns of precursory activity.

Volcanic thermal anomalies are monitored with an increased application of optical satellite sensors to improve the ability to identify renewed volcanic activity. Hotspot detection algorithms adopting a fixed threshold are widely used to detect thermal anomalies with a minimal occurrence of false alerts. However, when used on a global scale, these algorithms miss some subtle thermal anomalies that occur. Analyzing satellite data sources with machine learning (ML) algorithms has been shown to be efficient in extracting volcanic thermal features. Here, a data-driven algorithm is developed in Google Earth Engine (GEE) to map thermal anomalies associated with lava flows that erupted recently at different volcanoes around the world (e.g., Etna, Cumbre Vieja, Geldingadalir, Pacaya, and Stromboli). We used high spatial resolution images acquired by a Sentinel-2 MultiSpectral Instrument (MSI) and a random forest model, which avoids the setting of fixed a priori thresholds. The results indicate that the model achieves better performance than traditional approaches with good generalization capabilities and high sensitivity to less intense volcanic thermal anomalies. We found that this model is sufficiently robust to be successfully used with new eruptive scenes never seen before on a global scale.