| 1. |
- Greiner, Sonja H. M., et al.
(författare)
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Interaction between propagating basaltic dikes and pre-existing fractures : A case study in hyaloclastite from Dyrfjoll, Iceland
- 2023
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Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier. - 0377-0273 .- 1872-6097. ; 442
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Tidskriftsartikel (refereegranskat)abstract
- Magma in the Earth's crust is commonly transported through dikes. Fractures and faults, which are common in the shallow crust, form structural weaknesses that can act as energy-efficient propagation pathways. Although examples of this are known from active and extinct volcanoes in varying host rocks, the conditions and mechanisms of how and when dikes are influenced by these structures are not yet fully understood. This study investigates how basaltic dikes propagating through hyaloclastite in the shallow crust interact with pre-existing fractures. Using virtual 3D-models from drone-based photogrammetry, we mapped basaltic dikes exposed in a caldera-filling hyaloclastite in the extinct Dyrfjoll volcano, NE-Iceland, to measure the orientations of fractures and dikes, and quantify their interactions. We observe 39 changes in strike among 45 dikes and found a strong control of the governing stress field on orientations and interactions. Three types of dike-fracture interaction were identified: (1) Dikes propagating along pre-existing fractures. This is most frequently observed for dikes following the tectonic stress field. (2) Dikes with an abrupt change in strike occurring near or at a crosscutting fracture, but without magma flow into the fracture. (3) Dikes arrested at a crosscutting fracture. Such dikes may develop offshoots near the dike tip, which may approach the fracture at different angles and be able to cut across. Understanding how dikes interact with pre-existing fractures in moderately fractured host rock such as hyalo-clastite is relevant for hazard assessment and monitoring of volcanically active areas.
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| 2. |
- Hobe, Alex, et al.
(författare)
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Seismicity Patterns Due to Magma Intrusions Underneath Geothermal Power Plants
- 2021
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Ingår i: World Geothermal Congress 2020+1.
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Konferensbidrag (refereegranskat)abstract
- The Reykjanes Peninsula, Iceland, could soon see a once-in-a-millennium eruption, based on its current unrest and its historical record. This period of volcano-tectonic events threatens nearby airfields, geothermal power plants, and the capital, Reykjavik, where two thirds of Iceland’s population reside. The main sources of risk are lava, volcanic ash, and M > 6 earthquakes on large strike-slip faults. Six such known faults lie between 15-35 km from the capital. Here, we investigate whether such large earthquakes and/or an eruption are likely, based on the seismicity seen so far. To do so, we look for specific seismicity patterns indicative of magmatically-induced deformation, and compare seismicity overviews of the current unrest, previous decades, and swarm activity in the 1970s. We identify several cascades of boundary movements in both the current unrest and the 1970s activity, that have neighboring segments activate from east to west along the peninsula. This direction is reversed during the current unrest in a slower cascade, which ended with a ~30 km long boundary segment moving. Based on this and other observations, we suggest that magma intrusion has accelerated boundary deformation significantly. We identify another pattern, where seismicity and surface deformation in Svartsengi, the most seismically active region during this period, is greatly reduced when this activity swaps to the neighboring Reykjanes system. We suggest magma intrusion is halted in one volcanic system, in favor of intrusion in another, and describe several possible mechanisms.We further describe possible scenarios, and their likelihood, for the evolution of the current unrest, which range from a rapid return to quiescence, to full-scale eruption. Whichever scenario occurs, M > 6 earthquakes on known faults near Reykjavik are likely.
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| 3. |
- Juncu, Daniel, et al.
(författare)
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Injection-induced surface deformation and seismicity at the Hellisheidi geothermal field, Iceland
- 2020
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Ingår i: Journal of Volcanology and Geothermal Research. - : Elsevier BV. - 0377-0273 .- 1872-6097. ; 391
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Tidskriftsartikel (refereegranskat)abstract
- Induced seismicity is often associated with fluid injection but only rarely linked to surface deformation. At the Hellisheidi geothermal power plant in south-west Iceland we observe up to 2 cm of surface displacements during 2011–2012, indicating expansion of the crust. The displacements occurred at the same time as a strong increase in seismicity was detected and coincide with the initial phase of geothermal wastewater reinjection at Hellisheidi. Reinjection started on September 1, 2011 with a flow rate of around 500 kg/s. Micro-seismicity increased immediately in the area north of the injection sites, with the largest seismic events in the sequence being two M4 earthquakes on October 15, 2011. Semi-continuous GPS sites installed on October 15 and 17, and on November 2, 2011 reveal a transient signal which indicates that most of the deformation occurred in the first months after the start of the injection. The surface deformation is evident in ascending TerraSAR-X data covering June 2011 to May 2012 as well. We use an inverse modeling approach and simulate both the InSAR and GPS data to find the most plausible cause of the deformation signal, investigating how surface deformation, seismicity and fluid injection may be connected to each other. We argue that fluid injection caused an increase in pore pressure which resulted in increased seismicity and fault slip. Both pore pressure increase and fault slip contribute to the surface deformation.
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| 4. |
- Parks, Michelle M., et al.
(författare)
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2021-2023 Unrest and Geodetic Observations at Askja Volcano, Iceland
- 2024
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Ingår i: GEOPHYSICAL RESEARCH LETTERS. - 0094-8276 .- 1944-8007. ; 51:4
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Tidskriftsartikel (refereegranskat)abstract
- 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 similar to 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. 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, similar to 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). 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
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| 5. |
- Seaman, Paul, et al.
(författare)
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New multibeam mapping of the unique Ikaite columns in Ikka Fjord, SW Greenland
- 2022
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Ingår i: Marine Geology. - : Elsevier BV. - 0025-3227 .- 1872-6151. ; 444
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Tidskriftsartikel (refereegranskat)abstract
- Ikka Fjord in SW Greenland is world famous for its submarine, cold-water craving ikaite (CaCO3·6H2O) tufa columns. Due to the uniqueness of the columns, Ikka Fjord is declared a protected area by the Greenlandic authorities. In the summers of 2018–19, multibeam sonar bathymetry and aerial drone photogrammetric surveys were made in Ikka Fjord mapping and counting the columns and comparing the results to data from geophysical surveys of the fjord in 1995–96. The new surveys provide highly detailed maps of the fjord bathymetry and its columns, their height and position, and several hitherto unknown pockmarks in the seabed. A total of 938 individual columns and structures ranging 0.5–20 m in height from the sea floor were identified: a number surpassing the 678 taller columns (> 1 m) known from previous mapping. Our results support previous observations that the columns are restricted to the spatial extents of the Grønnedal-Íka igneous complex. The new survey data show that column distribution exhibits lineations and variable density over the fjord floor, notably that the innermost central deep part is free of columns. The tallest columns are observed to grow up to the halocline at approximately 2–4 m water depth. The majority of columns have reached only 15–50% of their growth potential. The ~60 columns of maximum growth stand in clusters, interpreted as representing exceptionally favourable growth settings. New seawater data collected in 2019 shows a worrying increase in temperature since the previous measurements in 1995 and 2007–2009, which could potentially affect the stability of the delicate columns of Ikka Fjord.
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