Volcanic eruptions are foundational events that shape the Earth's surface and provide a window into deep Earth processes. How the primary asthenospheric melts form, pond and ascend through the lithosphere is, however, still poorly understood. We document an on-going magmatic event offshore Mayotte Island (North Mozambique channel), associated with large surface displacements, very low frequency earthquakes and exceptionally deep (25-50 km) seismicity swarms. We present data from the May 2019 MAYOBS1 cruise, which reveal that this event gave birth to a 820m tall, ~ 5 km 3 deepsea volcanic edifice. This is the largest active submarine eruption ever documented. The data indicate that deep magma reservoirs were rapidly drained through dykes that intruded the entire lithosphere and that pre-existing subvertical faults in the mantle were reactivated beneath an ancient caldera structure.

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This report is the first in a series of reports replacing Publications 30 and 68 to provide revised dose coefficients for occupational intakes of radionuclides by inhalation and ingestion. The revised dose coefficients have been calculated using the Human Alimentary Tract Model (Publication 100) and a revision of the Human Respiratory Tract Model (Publication 66) that takes account of more recent data. In addition, information is provided on absorption into blood following inhalation and ingestion of different chemical forms of elements and their radioisotopes. In selected cases, it is judged that the data are sufficient to make material-specific recommendations. Revisions have been made to many of the models that describe the systemic biokinetics of radionuclides absorbed into blood, making them more physiologically realistic representations of uptake and retention in organs and tissues, and excretion. The reports in this series provide data for the interpretation of bioassay measurements as well as dose coefficients, replacing Publications 54 and 78. In assessing bioassay data such as measurements of whole-body or organ content, or urinary excretion, assumptions have to be made about the exposure scenario, including the pattern and mode of radionuclide intake, physical and chemical characteristics of the material involved, and the elapsed time between the exposure(s) and measurement. This report provides some guidance on monitoring programmes and data interpretation.

The influence of eustasy, tectonic deformation and sediment flux as controlling parameters on basin stratigraphy and depositional sequence development are largely accepted. Eustasy is usually considered as the dominant mechanism of sequence generation, especially for Pleistocene age successions. In active subduction margin settings, the high rates of tectonic deformation are expected to have a stronger influence on basin fill architecture, while sediment flux is generally less well constrained, and therefore less frequently considered. The active Hikurangi subduction margin in New Zealand offers the opportunity to quantitatively assess the relative roles of tectonic, climatic and eustatic drivers. We present a quantitative source-to-sink-like study of the Late Pleistocene succession from the Hawke's Bay sector of the inner forearc domain (c. 150 ka to Present). The interpretation of a grid of high-resolution marine seismic data, onland and offshore core and well descriptions, and the integration of geomorphic studies enabled identification of system tracts. In turn these comprise two sea-level-cycle depositional sequences (LPS1 and LPS2), including one complete 100 ka sequence (LPS1). Isopach maps of both sequences reveal changes in sediment distribution and preservation that reflect the relative roles of tectonic deformation and eustasy. Eustasy dominates development of 2 sequence architecture at relatively short time scales (i.e., < 20-30 kyrs), whereas tectonic deformation is increasingly important at longer time scales (≥100 kyrs). Four long-lasting depocenters are identified over the inner forearc domain and located in four subsiding basins (Kidnappers, Mahia, Lachlan and Motu-o-Kura basins). Significant shifts of the depocenter location in the basins are correlated with eustatic sea level changes. Estimates of sediment volumes and masses from isopach maps indicate higher mass accumulation rates during climato-eustatic extremes, which we correlated to the onland erosional response. Sediment distribution and landscape evolution are strongly influenced by the interaction of the structural deformation and sediment flux. We present paleogeographic reconstructions for the inner forearc domain coincident with two paleoclimatic extremes (Last Glacial Maximum and Holocene Optimum). These illustrate the importance of eustatic changes, structural deformation and sediment flux on the pattern of sediment distribution, accumulation and sequence architecture.

Volcanic eruptions are foundational events that shape the Earth's surface and provide a window into deep Earth processes. How the primary asthenospheric melts form, pond and ascend through the lithosphere is, however, still poorly understood. We document an ongoing magmatic event offshore Mayotte Island (North Mozambique channel), associated with large surface displacements, very low frequency earthquakes and exceptionally deep (25-50 km) seismicity swarms. We present data from the May 2019 MAYOBS1 cruise, which reveal that this event gave birth to a 820m tall, ~ 5 km 3 deepsea volcanic edifice. This is the largest active submarine eruption ever documented. The data indicate that deep magma reservoirs were rapidly drained through dykes that intruded the entire lithosphere and that pre-existing subvertical faults in the mantle were reactivated beneath an ancient caldera structure.

Detailed, high-resolution documentation of forearc basin fi ll is scarce in the literature.In this geological and geophysical study, we investigated the Pleistocene sedimentary rec ord of the tectonically active Hawke Bay forearc domain of the Hikurangi subduction margin of New Zealand. Interpretation of an extensive seismic-refl ection data set that is correlated with marine cores and onshore geological maps identifi es the detailed stratigraphic architecture of the last ~1.1 m.y. This analysis reveals the infl uences and interactions of tectonic deformation, climate, eustasy, and isostasy on forearc basin sedimentation. Eleven ~100 k.y. depositional sequences are recognized in the basin fi ll, thus highlighting the dominance of Pleistocene climate-eustasy on sequence development. The stacking pattern and isopach maps of sequences exhibit an overall retrogradational trend and an arcward migration of depocenters. These trends progressively develop a basinwide diachronous and composite erosion unconformity formed by the lateral succession and landward encroachment of the 12 sequence-bounding unconformities (S12 to S1). Among these, the S5 surface (ca. 430 ka) is an angular unconformity that separates major megasequences of the sedimentary record. The forearc domain evolved from a series of ridge-parallel basins to a succession of connected basins that have progressively developed around major, growing thrust-faulted ridges since ca. 430 ka. This change in basin confi guration and associated signifi cant increase of the preserved sediment fl uxes occurred synchronous with the reactivation of major out-of-sequence thrusts and the completion of the mid-Pleistocene transition.

Data on the gastrointestinal absorption of 12 elements have been reviewed. In each case, absorption is expressed as the fraction of the ingested element absorbed to blood, referred to as the f1 value, applying to intakes of unspecified chemical form by average population groups. The level of confidence in individual absorption values has been estimated in terms of lower and upper bounds, A and B, such that there is judged to be roughly a 90% probability that the true central value is no less than A and no greater than B. Ranges are proposed for intakes by adults, 10-year-old children and 3-month-old infants. Uncertainty in f1 values (B/A) ranged from 10% to factors of 100-400. The lowest uncertainties were for the well absorbed elements, H, I and Cs, for which there are good data, and the greatest uncertainties were for less well absorbed elements for which few data are available, particularly Zr and Sb. Ranges were generally wider for children and infants than for adults because of the need to allow for the likelihood of increased absorption with only limited data in support of the proposed values. The largest ranges were for 3-month-old infants, reflective lack of knowledge on the time-course and magnitude of possible increased absorption in the first few months of life. For each age group, ICRP values of absorption tend towards the upper bound of the ranges, indicating a degree of conservatism in th calculation of ingestion dose coefficients. Examination of the effect of the proposed confidence intervals for f1 values on uncertainties in dose coefficients for ingested radionuclides showed that there was no direct relationship. For some radionuclides, uncertainties in effective dose were small despite large uncertainties in f1 values while for others the uncertainties in effective doses approached the corresponding values for uncertainty in f1 values. These differences reflect the relative contributions to effective dose from cumulative activity in the contents of the alimentary tract, which in many cases is insensitive to uncertainties in f1, and cumulative activity of the absorbed radionuclide in systemic tissues, which is proportional to f1. In general, uncertainties in effective close for children and infants exceeded those in adults as a result of greater uncertainties in f1 values for the younger age groups. However, this effect was reduced in some cases by shorter retention times of absorbed nuclides in body tissues and organs.

International audienceHigh-resolution seismic data have been acquired in June 2008 on the Armorican Shelf (AS), in the northern Bay of Biscay, in order to reassess its stratigraphic architecture in detail and to study the impact of eustasy, tectonic and sediment delivery on the margin sedimentary record. Several profiles show fluvial-type incisions of several tens of meters (up to 54 m) associated to a widespread erosion surface. Several hypotheses are proposed for the stratigraphic position of this surface and incisions. We suggest Middle to Late Miocene age. Considering the relatively quiescent tectonic activity of the margin, we infer that the relative sea-level fall responsible of aerial incision on the Miocene shelf is eustasy-related. We propose the attested Serravallian–Tortonian eustatic lowstand (c. 11.6 Ma) as the key event responsible of such erosion and incision. This event marks the early beginning of the high-amplitude sea-level fluctuations that culminated during the Pleistocene and significantly controlled the present day AS morphology. The variability of vertical incision observed along single reaches can be explained by the confluence of several tributaries, the sinuosity of the channel and can be amplified by the unconsolidated nature of the Miocene substratum. The main pathways of the fluvial network corresponding to these buried valleys have been reconstructed and connections to other existing networks are proposed