Intermittent Growth of a Newly-Born Volcanic Island and Its Feeding System Revealed by Geological and Geochemical Monitoring 2013–2020, Nishinoshima, Ogasawara, Japan

The island-forming Nishinoshima eruptions in the Ogasawara Islands, Japan, provide a rare opportunity to examine how the terrestrial part of Earth’s surface increases via volcanism. Here, the sequence of recent eruptive activity of Nishinoshima is described based on long-term geological and geochemical monitoring of eruptive products. Processes of island growth and temporal changes in the magma chemistry are discussed. The growth of Nishinoshima was sustained by the effusion of low-viscosity andesite lava flows since 2013. The lava flows spread radially with numerous branches, resulting in compound lava flows. Lava flows form the coherent base of the new volcanic edifice; however, pyroclastic eruptions further developed the subaerial volcanic edifice. The duration of three consecutive eruptive episodes decreased from 2 years to a week through the entire eruptive sequence, with a decreasing eruptive volume and discharge rate through time. However, the latest, fourth episode was the most intense and largest, with a magma discharge rate on the order of 106 m3/day. The temporal change in the chemical composition of the magma indicates that more mafic magma was involved in the later episodes. The initial andesite magma with ∼60 wt% SiO2 changed to basaltic andesite magma with ∼55 wt% SiO2, including olivine phenocryst, during the last episode. The eruptive behavior and geochemical characteristics suggest that the 2013–2020 Nishinoshima eruption was fueled by magma resulting from the mixing of silicic and mafic components in a shallow reservoir and by magma episodically supplied from deeper reservoirs. The lava effusion and the occasional explosive eruptions, sustained by the discharge of magma caused by the interactions of these multiple magma reservoirs at different depths, contributed to the formation and growth of the new Nishinoshima volcanic island since 2013. Comparisons with several examples of island-forming eruptions in shallow seas indicate that a long-lasting voluminous lava effusion with a discharge rate on the order of at least 104 m3/day (annual average) to 105 m3/day (monthly average) is required for the formation and growth of a new volcanic island with a diameter on km-scale that can survive sea-wave erosion over the years.

Origins of Vulcanello based on the re-examination of historical sources (Vulcano, Aeolian Islands)

The lava platform and the three pyroclastic cones of Vulcanello constitute the northernmost volcanic structure of the island of Vulcano (Aeolian Islands). The sandy isthmus connecting the platform to the main island was definitively formed in the first half of the 1500s; before then, Vulcano and Vulcanello were two close but separate islands. For a long time, the interpretation of the sources of the II-I century BC, had considered the islet as built up about 2200 years ago. This belief, which proliferated among naturalists from the 17th century, is not confirmed in the ancient texts or even in the geographical documents of the time, which do not indicate the presence of Vulcanello as a new and stable island near Vulcano. The islet would only be mentioned at the dawn of the second millennium, and named in Arabic “Gabal’ al Burkān”, meaning Mount of Vulcano; shortly thereafter the toponym changed to the Latin “Insulam Vulcanelli” and then, towards the 15th century, finally to Vulcanello. Since the creation of a volcanic island certainly occurred in the Aeolian Islands in the classical era, but traces of it were quickly lost, the most plausible hypothesis is that it was formed in the area of the current Vulcanello, to be subsequently erased by the sea. The shallow, flat seabed, likely remaining as a result of sea abrasion, might have represented the morphological element on which the circular lava platform we know today was formed sometime between 950 and 1000 AD.

Sequestration of P fractions in the soils of an incipient ferralisation chronosequence on a humid tropical volcanic island

Background Phosphorus (P) is the limiting nutrient in many mature tropical forests. The ecological significance of declining P stocks as soils age is exacerbated by much of the remaining P being progressively sequestered. However, the details of how and where P is sequestered during the ageing in tropical forest soils remains unclear. Results We examined the relationships between various forms of the Fe and Al sesquioxides and the Hedley fractions of P in soils of an incipient ferralitic chronosequence on an altitudinal series of gently sloping benches on Green Island, off the southeastern coast of Taiwan. These soils contain limited amounts of easily exchangeable P. Of the sesquioxide variables, only Fe and Al crystallinities increased significantly with bench altitude/soil age, indicating that the ferralisation trend is weak. The bulk of the soil P was in the NaOH and residual extractable fractions, and of low lability. The P fractions that correlated best with the sesquioxides were the organic components of the NaHCO3 and NaOH extracts. Conclusions The amorphous sesquioxides, Feo and Alo, were the forms that correlated best with the P fractions. A substantial proportion of the labile P appears to be organic and to be associated with Alo in organic-aluminium complexes. The progression of P sequestration appears to be slightly slower than the chemical and mineralogical indicators of ferralisation.

Commensal Rodent Habitat Expansion Enhances Arthropod Disease Vectors on a Tropical Volcanic Island

On volcanic islands, the release of animals from predators and competitors can lead to increased body size and population density as well as the expanded habitat use of introduced animals relative to their mainland counterparts. Such alterations might facilitate the spread of diseases on islands when these exotic animals also carry pathogenic agents; however, this has rarely been investigated. The commensal Asian house rat (Rattus tanezumi) is confined to human residential surroundings in mainland Taiwan but can be observed in the forests of nearby Orchid Island, which is a tropical volcanic island. Orchid Island is also a hot spot for scrub typhus, a lethal febrile disease transmitted by larval trombiculid mites (chiggers) that are infected primarily with the rickettsia Orientia tsutsugamushi (OT). We predicted an increase in chigger abundance when rodents (the primary host of chiggers) invade forests from human settlements since soils are largely absent in the latter habitat but necessary for the survival of nymphal and adult mites. A trimonthly rodent survey at 10 sites in three habitats (human residential, grassland, and forest) found only R. tanezumi and showed more R. tanezumi and chiggers in forests than in human residential sites. There was a positive association between rodent and chigger abundance, as well as between rodent body weight and chigger load. Lastly, >95% of chiggers were Leptotrombidium deliense and their OT infection rates were similar among all habitats. Our study demonstrated potentially elevated risks of scrub typhus when this commensal rat species is allowed to invade natural habitats on islands. Additionally, while the success of invasive species can be ascribed to their parasites being left behind, island invaders might instead obtain more parasites if the parasite requires only a single host (e.g., trombiculid mite), is a host generalist (e.g., L. deliense), and is transferred from unsuitable to suitable habitats (i.e., human settlements on the mainland to forests on an island).

Assessing potential impact of explosive volcanic eruptions from Jan Mayen Island (Norway) on aviation in the North Atlantic

Volcanic eruptions are amongst the most jeopardizing natural events due to their potential impacts on life, assets, and environment. In particular, atmospheric dispersal of volcanic tephra and aerosols during the explosive eruptions poses a serious threat to life and has significant consequences for infrastructures and global aviation safety. The volcanic island of Jan Mayen, located in the North Atlantic under trans-continental air traffic routes, is considered the northernmost active volcanic area in the world, with at least five eruptive periods recorded during the last 200 years. However, quantitative hazard assessments on the possible consequences for air traffic of a future ash-forming eruption are nonexistent. This study presents the first comprehensive long-term volcanic hazard assessment for Jan Mayen volcanic island in terms of ash dispersal and airborne tephra concentration at different flight levels. In order to delve in the characterization and modelling of that potential impact, a probabilistic approach based on merging a large number of numerical simulations is adopted, varying the volcano’s Eruptive Source Parameters (ESPs) and meteorological scenario. Each ESP value is randomly sampled following a continuous Probability Density Function (PDF) defined from the Jan Mayen geological record. Over 20 years of climatic data are considered in order to explore the natural variability associated with meteorological conditions and used to run thousands of simulations of the ash dispersal model FALL3D on a 2 km-resolution grid. The simulated scenarios are combined to produce probability maps of airborne ash concentration, arrival time and persistence at different flight levels in the atmosphere. The resulting maps represent an aid to civil protection, decision makers and aviation stakeholders in assessing and preventing the potential impact from a future eruption at Jan Mayen.