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The North Atlantic Ocean and its margins present important, unanswered geodynamics questions, both in the continental and oceanic domains. To better understand the structure and evolution of this area, a set of 18 state-of-the-art ocean-bottom seismometers (OBSs) have been deployed in the North Atlantic Ocean in September 2018 as part of the project SEA-SEIS (Structure, Evolution And Seismicity of the Irish offshore). The network covers the entire Irish offshore and parts of the UK and Iceland waters. Over a period of 15 months, they will record seismic data at 1-4 km depths on the ocean bottom, with the retrieval planned for April, 2020. With this new broadband data, together with all other globally available broadband data, we will improve the tomographic resolution of the North Atlantic region, including the Iceland hotspot. To image the lithosphere and mantle, structural information will be extracted from the large amount of vertical- and transverse-component waveform fits, including the unique new OBS data, using the Automated Multimode Inversion (AMI) of surface, S- and multiple S-waves. Realistic body-wave sensitivity kernels will be developed and integrated into the inversion. The improved tomographic models of the North Atlantic region should yield new insights into the origins of the enigmatic North Atlantic Igneous Province volcanism, the evolution and deep structure of the Iceland Hotspot and its effect on the evolution of the region. To minimize the effect of data errors on the model, extensive quality control has been applied to the available global and regional network data, including extensive checks of the correctness of the instrument response information, which can influence the accuracy of the structural information yielded by seismograms. The quality control revealed a number of problems with the response files at stations from various of networks. The problems are being fixed in joint efforts with the data centers and network operators. [ABSTRACT FROM AUTHOR]

Surtsey is a basaltic island in the south-western end of Vestmannaeyjar archipelago off the south coast of Iceland and is a part of the Vestmannaeyjar volcanic system. It is built from the ocean floor at about 130 m depth in a series of eruptions during 1963-1967, one of the longest eruption in Iceland in historical times. The eruptions can be split into four phases. The first phase of the eruptions was explosive and phreatomagmatic in character. The aim of this study is to put constraints on the mass of tephra transported with the plume. This is done in two ways: (1) Study soil profiles on Heimaey and on the mainland to look for tephra deposits from Surtsey as well as note contemporary descriptions of tephra fallout; and (2) by compiling existing contemporary records of plume height and use plume height – mass transport systematics to estimate the transport. Finally, we compare the outcomes of (1) and (2). Eruption started on 14 November 1963. It was explosive and fed an eruption plume rising typically to 5-9 km in November and December 1963. The plume was usually bent over or straight, steam-rich and the activity alternated between frequent explosions forming a continuous plume and periods of continuous uprush. Fallout according to weather records from the time was primarily towards north and south. Tephra fallout was mostly into the ocean around the island, but did occur on several occasions on the inhabited Heimaey, 20 km to the northeast of Surtsey. Some fallout was also detected on the mainland of Iceland about 40 km away from Surtsey. Preliminary results indicate that minor amounts of tephra are preserved in Heimaey and that only traces of tephra may be present on the mainland while a discernible tephra layer is not preserved in soil. Data on fallout into the ocean is scarce or non-existent. However, the data indicate that the fraction of airborne tephra relative to the submarine and near-vent deposition is volumetrically minor. [ABSTRACT FROM AUTHOR]

The formation of the oceanic island Surtsey in the shallow ocean off the south coast of Iceland in 1963-1967 remains one of the best-studied examples of basaltic emergent volcanism to date. Cycles of the phreatomagmatic explosive activity occurred several times during the eruptions: (1) At the onset of the eruption - eruption of Surtur crater, November 1963-January 1964; (2) The submarine eruption of Surtla - December 1963; (3) the formation of the parasitic cone of Surtungur - January-April 1964; (4) formation of the temporary island of Syrtlingur - May-October 1965; and (5) the formation of the temporary island of Jólnir - December 1965-August 1966. Explosive activities at these vents are well-documented and preserved in photographic records and reports. The first submarine volcanic activity was detected on 14th of November 1963 where ocean depth was 130 m prior to the eruption. The onset time of the submarine eruption was not resolved in contemporary records. Birth of the submarine eruption at the seafloor can be detected by investigation of tremor signals or any unusual 0seismic activity at nearby seismograms. Seismic records from the time of the Surtsey eruption are available from two permanent seismic stations in south Iceland: Reykjavík in southwest Iceland and Kirkjubæjarklaustur in southeast Iceland. These records have now been re-analyzed. Any potential eruption signals are drowned by microseisms at the Reykjavík station while at the Kirkjubæjarklaustur station eruption tremor signals appeared before the first explosive eruption had broken through the sea floor. Earthquake activity related to the beginning of the eruption was weak, hardly detectable by the existing seismograph stations.These observations indicate that the actual start of the submarine eruption occurred no later than on 13th of November, with eruption tremors recorded 18-24 hours before the first visual observation of eruption from a fishing boat in the early morning of the 14th of November. Similar tremors were also detected during other four explosive phases. The potential of seismic records to detect the onset of eruptions is demonstrated through these results. Based on the shreds of evidence for the onset time and the visual observations, maps and descriptions, we derive the early growth history of Surtsey. When combined with bathymetric data prior to the eruption, we obtain constraints on the rate of submarine cone buildup. This places constraints on the eruption rate in these early submarine-to-emergent phases of the eruption. Early results indicate that the maximum mass eruption rate in the beginning phase was relatively modest, below 1,000,000 kg/s. [ABSTRACT FROM AUTHOR]