Unrest began in July 2021 at Askja volcano in the Northern Volcanic Zone (NVZ) of Iceland. Its most recent eruption, in 1961, was predominantly effusive and produced ∼0.1 km3 lava field. The last ...plinian eruption at Askja occurred in 1875. Geodetic measurements between 1983 and 2021 detail subsidence of Askja, decaying in an exponential manner. At the end of July 2021, inflation was detected at Askja volcano, from GNSS observations and Sentinel‐1 interferograms. The inflationary episode can be divided into two periods from the onset of inflation until September 2023. An initial period until 20 September 2021 when geodetic models suggest transfer of magma (or magmatic fluids) from within the shallowest part of the magmatic system (comprising an inflating and deflating source), potentially involving silicic magma. A following period when one source of pressure increase at shallow depth can explain the observations.
Plain Language Summary
Askja volcano, situated in the Northern Volcanic Zone in Iceland, has been quiet since its last eruption in 1961, with surface deformation measurements from 1983 to 2021 displaying a decaying subsidence signal within the Askja caldera. However, at the end of July 2021, the volcano began to inflate. This was detected on both GNSS and satellite observations. As of September 2023, ∼65 cm of uplift had been measured at GNSS station OLAC. Modeling of surface deformation measurements indicates that the inflation was triggered by upward migration of melt (or magmatic fluids).
Key Points
At the end of July 2021, Askja volcano began to inflate—detected on both GNSS and satellite observations, ending 1983–2021 subsidence
Geodetic modeling indicates upward migration of magma, feeding a magma body at an inferred depth of 2.5–3.1 km under the main Askja caldera
Start of unrest was associated with magma transfer within the upper part of the system, followed by possible additional influx from depth
Grímsvötn Volcano is the most active volcano in Iceland, and its last three eruptions were in 1998, 2004, and 2011. Here we analyze the displacement around Grímsvötn during these last three eruptive ...cycles using 10 GPS stations. The observed displacements in this region generally contain a linear component of tectonic and glacio‐isostatic origin, in agreement with the previously estimated values of plate motions and vertical rebound. Larger amplitude deformation observed close to Grímsvötn at the GFUM continuous GPS station clearly reflects a major volcanic contribution superimposed on a tectonic component. We estimate and subtract the tectonic trend at this station using regional observed displacement. The direction and pattern of the residual volcanic displacement (for coeruptive and intereruptive periods) are consistent for all three of these eruptive cycles. The posteruptive inflation is characterized by an exponential trend, followed by a linear trend. In this study, we explain this temporal behavior using a new analytic model that has two connected magma chambers surrounded by an elastic medium and fed by a constant basal magma inflow. During the early posteruptive phase, pressure readjustment occurs between the two reservoirs, with replenishment of the shallow chamber from the deep chamber. Afterward, due to the constant inflow of magma into the deep reservoir, the pressurization of the system produces linear uplift. A large deep reservoir favors magma storage rather than surface emission. Based on displacement measured at GFUM station, we estimate an upper limit for the radius of the deep reservoir of ∼10 km.
Key Points
GPS time series for the last three intereruptive cycles of Grimsvotn are analyzed
We propose a model with two connected magmatic chambers, with basal magma inflow
The vertical deformation limits the lateral extension of the deep reservoir
The marine Ikka Fjord in Greenland is well known for its remarkable submarine columns made of the cold-carbonate ikaite (CaCO3·6H2O). Here, natural processes lead to fast-precipitating ikaite at low ...temperatures (< 10°C) when carbonate-bearing groundwater seeps through fractures in Ikka Fjord and mixes with seawater. Within an area of 0.75 km2, 678 columns of 1 – 20 meters height have been registered, continuously growing at rates measured at 50 cm per year. Understanding this natural system is of importance for carbon capture and storage efforts as it represents a very efficient method for carbon mineral storage in cold seawater.
Based on hydrochemical monitoring, petrological observations, and geochemical modeling, we identify a mechanism and estimate a time scale for fault healing after an earthquake. Hydrochemical ...monitoring of groundwater samples from an aquifer, which is at an approximate depth of 1200 m, was conducted over a period of 10 years. Groundwater samples have been taken from a borehole (HU‐01) that crosses the Húsavík‐Flatey Fault (HFF) near Húsavík town, northern Iceland. After 10 weeks of sampling, on 16 September 2002, an M 5.8 earthquake occurred on the Grimsey Lineament, which is approximately parallel to the HFF. This earthquake caused rupturing of a hydrological barrier resulting in an influx of groundwater from a second aquifer, which was recorded by 15–20% concentration increases for some cations and anions. This was followed by hydrochemical recovery. Based on petrological observations of tectonically exhumed fault rocks, we conclude that hydrochemical recovery recorded fault healing by precipitation of secondary minerals along fractures. Because hydrochemical recovery accelerated with time, we conclude that the growth rate of these minerals was controlled by reaction rates at mineral‐water interfaces. Geochemical modeling confirmed that the secondary minerals which formed along fractures were saturated in the sampled groundwater. Fault healing and therefore hydrochemical recovery was periodically interrupted by refracturing events. Supported by field and petrographic evidence, we conclude that these events were caused by changes of fluid pressure probably coupled with earthquakes. These events became successively smaller as groundwater flux decreased with time. Despite refracturing, hydrochemical recovery reached completion 8–10 years after the earthquake.
Key Points
Hydrochemical monitoring records fault healing after an earthquakeMineral growth along fractures is surface controlledThe time scale of fault healing is 8–10 years
The submarine tufa columns of Ikka Fjord in Southwest Greenland have been studied during multiple field campaigns since 1995. The fjord contains close to thousand columns previously shown to consist ...of the metastable carbonate mineral ikaite (CaCO3·6H2O), which requires near-freezing conditions to remain stable over longer periods of time. During a field campaign to Ikka Fjord in the summer of 2019, seawater temperatures of 6–9 °C and visual physical changes to the columns were observed. These are the highest recorded seawater temperatures measured in Ikka Fjord in over three decades of research. In response, three selected columns at three different locations were sampled at their bases, middle, and top sections for mineralogical analysis. These samples were supplemented by a four further column samples and an extensive hydrographical campaign during fieldwork in the summer 2021. Here, we report the results of the mineralogical analyses performed by X-ray diffraction and µ-Raman Spectroscopy on these column samples. The results show that the columns analysed now consist of the less hydrated carbonate minerals, monohydrocalcite (CaCO3·H2O), aragonite, and calcite (CaCO3). One of the columns has completely altered into monohydrocalcite, whereas the other columns have crusts of ikaite and cores of monohydrocalcite ± aragonite and calcite. This change is interpreted as a dehydration reaction and mineral alteration from ikaite to monohydrocalcite continuing to aragonite ± calcite in response to being bathed in warming seawater. Hydrographic profilers and static dataloggers recorded seawater temperatures of 4–8 °C in the column-containing fjord areas during June–August 2021. The upper parts of the columns are particularly exposed to temperatures > 6 °C, considered to be the long-term stability threshold of ikaite in Ikka Fjord. The mineral dehydration reactions are irreversible. It is therefore predicted in a warming Arctic, ikaite will only appear as new growth on the columns for a short period, and that with time, the columns of Ikka Fjord will change mineralogy into mainly monohydrocalcite.
Impacts are common geologic features on the terrestrial planets throughout the solar system, and on at least Earth and Mars impacts have induced hydrothermal convection. Impact-generated hydrothermal ...systems have been suggested to possess the same life supporting capability as hydrothermal systems associated with volcanic activity. However, evidence of fossil microbial colonization in impact-generated hydrothermal systems is scarce in the literature. Here we report of fossilized microorganisms in association with cavity-grown hydrothermal minerals from the 458 Ma Lockne impact structure, Sweden. Based on morphological characteristics the fossilized microorganisms are interpreted as fungi. We further infer the kerogenization of the microfossils, and thus the life span of the fungi, to be contemporaneous with the hydrothermal activity and migration of hydrocarbons in the system. Our results from the Lockne impact structure show that hydrothermal systems associated with impact structures can support colonization by microbial life.
The local geology at Kloxåsen is characterised by ejecta deposits from the 458 Ma Lockne marine impact. The Kloxåsen ejecta are located on a Caledonian parautochthonous unit, approximately 7 km from ...the centre of the 7.5-km-wide Lockne crater structure. The ejecta were deposited on the seafloor and were covered with seawater immediately after the impact event. Of special interest is a mafic impact breccia within the ejecta, which before the impact was Åsby dolerite that belongs to the Jämtland suite of the 1.25 Ga Central Scandinavian Dolerite Group. The mafic impact breccia occurs mainly as a coherent thin domain within a larger block of granitic breccia, which we interpret as a result of the in situ brecciation of a dolerite sill within granitic bedrock. Shock pressure in the doleritic breccia was low, in the order of 0.4 GPa, constrained by the presence of mechanically twinned clinopyroxene. Low shock pressure and brecciation corresponds well to the spall zone of an impact crater, where ejecta originate from. Whereas spalled ejecta can also show signs of having been exposed to high shock pressures, including shocked quartz, evidence for this was not found in the Kloxåsen ejecta. The breccia has been hydrothermally altered, but the ejecta are too far removed from the crater to have been affected by hydrothermal circulation in relation to Lockne's impact event. Fluid inclusion analyses suggest that most of the alteration happened later, during the Caledonian orogeny. Geochemical analyses reflect observed mineral alterations well, such as serpentinisation of olivine.
We analyze data spanning up to 5 years from 18 continuous GPS stations in Iceland, computing daily positions of the stations with three different high‐level geodetic processing software packages. We ...observe large‐scale crustal deformation due to plate spreading across Iceland. The observed plate divergence between the North American and the Eurasian plates is in general agreement with existing models of plate motion. Spreading is taken up within a ∼100–150 km wide plate boundary zone that runs through the island. Of the two parallel branches of the plate boundary in south Iceland, the eastern volcanic zone is currently taking up the majority of the spreading and little is left for the western volcanic zone. The plate boundary deformation field has been locally and temporarily affected in south Iceland by two Mw = 6.5 earthquakes in June 2000, inflation at Katla volcano during 2000 to 2004, and an eruption of Hekla volcano in February 2000. All stations with significant vertical velocities are moving up relative to the reference station REYK, with the highest velocity exceeding 20 mm/yr in the center of the island.
Katla and Eyjafjallajökull volcanoes are situated 25 km apart at the southern tip of the Eastern Volcanic Zone in Iceland. Both have been active in historic time (last 1100 years) and have a history ...of simultaneous activity. The much more active Katla volcano has erupted at least 20 times, and Eyjafjallajökull's two eruptions were contemporaneous with Katla eruptions. Following a quiet period of several decades, the seismicity beneath Eyjafjallajökull was high in 1994 and again in 1999. The activity culminated in July 1999 when a flash flood occurred from the Mýrdalsjökull ice cap covering Katla, associated with changes in seismicity, bursts of volcanic tremor, and the formation and deepening of ice cauldrons. We report here results of deformation observations of these events, both by GPS geodesy and tilt measurements. The 1999 increase in seismicity at Eyjafjallajökull was associated with significant inflation of the volcano. The deformation data are modeled by a point pressure source at 3.5 km depth beneath the flank of the volcano, about 4 km south of the summit crater. Maximum uplift of the model is 0.35 m. A similar model also explains deformation associated with the 1994 seismic crisis. The deformation field of the Katla volcano is more difficult to ascertain due to the extensive glacier coverage. Movements of points on nunataks on and near the caldera rim indicate inflation and magma movements at shallow level beneath the caldera in connection with the events of July 1999.
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