Nordic Cancer Union

<p>Geodetic observations during volcanic eruptions are important to constrain from where the eruptive products originate in the sub-surface. Some eruptions are sourced from magma reservoirs shallow in the crust, whereas others may tap magma directly from the mantle. The 2021 Fagradalsfjall eruption took place on the Reykjanes Peninsula, Iceland, during March 19 to September 18, resulting in approximately 0.15 km<sup>3</sup> of erupted basaltic lava. A wide-spread crustal subsidence and inward horizontal motion, centered on the eruptive site, was observed during the eruption. Nearest to the emplaced lava flows, additional localized subsidence is observed due to the loading of the lavas. The regional subsidence rate varied during the eruption: it was low in the beginning and then increased, in broad agreement with changes in the bulk effusive rate. In this study we use GNSS and InSAR data to model the deformation source(s) during different periods of the eruption, primarily aiming to resolve the depth and volume change of the magma source. We furthermore calculate crustal stress changes during the eruption and compare to the regional seismicity.</p>

Abstract We present a 500‐year history of naturally felled driftwood incursion to northern Svalbard, directly reflecting regional sea ice conditions and Arctic Ocean circulation. Provenance and age determinations by dendrochronology and wood anatomy provide insights into Arctic Ocean currents and climatic conditions at a fine spatial resolution, as crossdating with reference chronologies from the circum‐Arctic boreal forests enables determination of the watershed the driftwood originated from. Sample crossdating may result in a wide range of matches across the pan‐boreal region, which may be biased toward regions covered by the reference chronologies. Our study considers alternate approaches to selecting probable origin sites, by weighting scores via reference chronology span and visualizing results through spatiotemporal density plots, as opposed to more basic ranking systems. As our samples come from naturally felled trees (not logged or both), the relative proportions of different provenances are used to infer past ocean current dominance. Our record indicates centennial‐to decadal‐scale shifts in source regions for driftwood incursion to Svalbard, aligning with Late Holocene high variability and high frequency shifts in the Transpolar Drift and Beaufort Gyre strengths and associated fluctuating climate conditions. Driftwood occurrence and provenance also track the northward ice formation shift in peripheral Arctic seas in the past century. A distinct decrease in driftwood incursion during the last 30 years matches the observed decline in pan‐Arctic sea ice extent in recent decades. Our new approach successfully employs driftwood as a proxy for Arctic Ocean surface circulation and sea ice dynamics.

U-Pb zircon single grain dating using the LA-MC-ICP-MS technique was utilized to determine the age of the host rocks of the Juomasuo Au-Co-Cu deposit located in the late Archean Kuusamo supracrustal belt. Even though the dated samples have diverse geochemical signatures that imply felsic volcanic and sedimentary precursors, the U-Pb data revealed heterogeneous detrital zircon populations for all samples. The host rocks are thus considered to belong to reworked sedimentary/volcano-sedimentary sequences. The maximun depositional ages of the samples fall in the 2.75-2.65 Ga age window, and no Paleoproterozoic ages were recovered in the examined zircon grains (151 analytical spots in total). In addition, a younger population (2.65-2.60 Ga) of internally featureless, BSE-pale/CL-dark zircon and zircon domains, was found in the mineralized sequences. These homogenized zircon grains resemble zircon formed in postmagmatic solid-state processes, in which zircon is recrystallized in metamorphichydrothermal conditions. This metamorphic-hydrothermal event most probably occurred in the original provenance area of the metasedimentary rocks.

The presence of Fe- and Si-rich liquids found as melt inclusions in apatite and olivine in the Upper Zone of the Skaergaard intrusion, East Greenland, demonstrates the occurrence of liquid immiscibility in the late-stage evolution of tholeiitic magmas in a plutonic setting. However, it remains unclear at which stage of crystallization unmixing began. To constrain the onset and the petrological importance of liquid immiscibility in the Skaergaard and tholeiitic magmas in general, we have studied crystallized melt inclusions entrapped in early primocryst plagioclase. Such melt inclusions become abundant from the top of the Lower Zone and upwards in the Layered Series, in primocryst plagioclase of composition An54^26. The daughter phase assemblage is the same in all the inclusions, although the modal proportions of the daughter phases are highly variable: plagioclase (42^59%), clinopyroxene (28^41%), ilmenite (4^9%), magnetite (3^10%), apatite (1^9%) and accessory phases (51%). Accordingly, the bulk compositions of reheated and homogenized melt inclusions show large variations in SiO2 (40^54 wt %), FeO t (7^23 wt %), P 2O5 (0^1 ·9 wt %) and K2 O( 0^2·8 wt %), and have variable CaO/Al2O3 ratios.These variations are best explained by trapping of varying proportions of immiscible iron- and silica-rich melts and demonstrate that liquid immiscibility started in the upper part of the Lower Zone. We conclude that a significant part of the Skaergaard intrusion crystallized from an emulsion of Fe- and Si-rich immiscible melts.The heterogeneous trapping of a mixture of Fe- and Si-rich immiscible liquids in primocryst plagioclase indicates that the dispersed droplets in the Lower and Middle Zones were smaller than the size of the inclusion (5500mm). In the Upper Zone, most of the inclusions in apatite are composed of the conjugate end-member liquids, indicating a larger size for the dispersed droplets. Metre-sized pods and layers of melanogranophyre in the upper part of the intrusion are believed to represent pooled bodies of the immiscible Si-rich liquid. Differentiation of an emulsified magma must be considered in petrogenetic models for the Skaergaard intrusion.

The load on the crust from the ~ 0.8 km3 of eruptive products of the Surtsey eruption is expected to lead to subsidence of the Surtsey island by sagging of the lithosphere, compaction of material, and slumping of the volcanic edifice. immediately after the eruption ended in the summer of 1967 a levelling line was established across the island to monitor this expected subsidence. The line originally contained 42 benchmarks. As Surtsey is subjected to extensive erosion, in particular in the western and southern parts of the island, the western section of the line has been lost to the sea. in the year 2002 the line ended with benchmark 28. Additional benchmarks were installed 1979, 1982, 1985 and 2002, to fill in gaps in the original line and another profile was installed through the Surtur i crater. Between 1967 and 2002 levelling has been performed eleven times. one benchmark was surveyed with geodetic GPS in 1992. The benchmark was resurveyed in 2000 and 2002 and the GPS network has been extended to comprise four points. in this report we have compiled the levelling data collected on Surtsey so far. Furthermore we present coordinates for the GPS-benchmarks. Continuing subsidence of Surtsey is observed with a decaying rate. The area around the Surtur i crater is the most stable part with a subsidence rate of 0.7 cm/yr in the period 1991–2002. The largest subsidence is observed at the flanks of the island with rates up to 1.4 cm/yr. The excess rate here is most likely caused by slumping of the sides of the island.

Tephra-grain counting, morphology and geochemistry in the 150–1000 μm size fraction were used to identify 22 individual tephra horizons and one visible tephra layer (Saksunarvatn) from postglacial sediment of the north Iceland shelf. Core MD99-2269 (66°37.53‘N, 20°51.16‘W, water depth 365 m, length 2533 cm) from the Reykjafjardaráll basin is constrained at the base by the Vedde tephra (c. 12 000 cal. yr BP). Geochemical analyses and stratigraphical position of the 22 tephra horizons were used to identify the following cryptotephras: KOL-1372 (AD 1372), Hekla 1104 (AD 1104), Snæfellsnes 1 (c. 1790 cal. yr BP), Hekla 3 (c. 2970 cal. yr BP), Hekla 4 (c. 4230 cal. yr BP), TV 5 (c. 6860 cal. yr BP) and Suduroy (c. 8070 cal. yr BP). A tephra of the same geochemistry as KOL-1372 was found near the base of the core and is here named KOL3-2269 (>11 000 cal. yr BP). Eleven additional cryptotephras were geochemically typed to their respective Icelandic volcanic centres of origin and their ages constrained. Four tephra horizons had a very heterogeneous geochemical signal and may reflect secondary rather than primary deposition although we speculate whether the heterogeneity may be due to mixing of distinct cryptotephras within our sample. The cryptotephras and one visible tephra layer (Saksunarvatn) were intercalibrated with the combined MD99-2269 and MD99-2322 (67°08.18‘N, 30°49.67‘W, 714 m water depth, length 2617 cm) palaeomagnetic secular variation record, in depth and on a calibrated radiocarbon chronology, providing a fundamental chronological and stratigraphic template for future studies of environmental and volcanic variability for the Icelandic region, eastern North Atlantic and NW Europe.

We present InSAR observations of deformation due to an intrusion in the Eyjafjallajökull volcano, Southern Iceland, in 1994. More than 15 cm of deformation in the line of sight (LOS) direction is detected in a series of interferograms spanning a micro‐earthquake swarm occurring in June 1994. The location of the seismicity is more than 6 km offset compared to the area of inferred maximum surface uplift. Through an inversion scheme we find that a horizontal sill intrusion experiencing variable opening of up to 0.36 m agrees well with the deformation data. The total intrusion volume is 0.017 km3. The northern periphery of the modeled intrusion fits well with the area of recorded seismicity, indicating a close connection. Several processes may be responsible. Our preferred explanation is that the earthquakes are caused by opening of a narrow magma channel from depth, feeding the sill.