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The fissure swarm of the Askja volcanic system along the divergent plate boundary of N Iceland

Abstract

Divergent plate boundaries, such as the one crossing Iceland, are characterized by a high density of subparallel volcanic fissures and tectonic fractures, collectively termed rift zones, or fissure swarms when extending from a specific volcano. Volcanic fissures and tectonic fractures in the fissure swarms are formed during rifting events, when magma intrudes fractures to form dikes and even feeds fissure eruptions. We mapped volcanic fissures and tectonic fractures in a part of the divergent plate boundary in northern Iceland. The study area is ~1,800 km2, located within and north of the Askja central volcano. The style of fractures changes with distance from Askja. Close to Askja the swarm is dominated by eruptive fissures. The proportion of tectonic fractures gets larger with distance from Askja. This may indicate that magma pressure is generally higher in dikes close to Askja than farther away from it. Volcanic fissures and tectonic fractures are either oriented away from or concentric with the 3–4 identified calderas in Askja. The average azimuth of fissures and fractures in the area deviates significantly from the azimuth perpendicular to the direction of plate velocity. As this deviation decreases gradually northward, we suggest that the effect of the triple junction of the North American, Eurasian and the Hreppar microplate is a likely cause for this deviation. Shallow, tectonic earthquakes in the vicinity of Askja are often located in a relatively unfractured area between the fissure swarms of Askja and Kverkfjöll. These earthquakes are associated with strike-slip faulting according to fault plane solutions. We suggest that the latest magma intrusions into either the Askja or the Kverkfjöll fissure swarms rotated the maximum stress axis from being vertical to horizontal, causing the formation of strike-slip faults instead of the dilatational fractures related to the fissure swarms. The activity in different parts of the Askja fissure swarm is uneven in time and switches between subswarms, as shown by a fissure swarm that is exposed in an early Holocene lava NW of Herðubreið but disappears under a younger (3500–4500 BP) lava flow. We suggest that the location of inflation centres in Askja central volcano controls into which part of the Askja fissure swarm a dike propagates. The size and amount of fractures in the Kollóttadyngja lava shield decrease with increasing elevation. We suggest that this occurred as the depth to the propagating dike(s) was greater under central Kollóttadyngja than under its flanks, due to topography.

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References

  • Acocella V, Korme T, Salvini F, Funiciello R (2003) Elliptic calderas in the Ethiopian Rift: control of pre-existing structures. J Volcanol Geotherm Res 119(1–4):189–203

    Article  Google Scholar 

  • Baer G, Hamiel Y, Shamir G, Nof R (2008) Evolution of a magma-driven earthquake swarm and triggering of the nearby Oldoinyo Lengai eruption, as resolved by InSAR, ground observations and elastic modeling, East African Rift, 2007. Earth Planet Sci Lett 272(1–2):339–352. doi:310.1016/j.epsl.2008.1004.1052

    Article  Google Scholar 

  • Bjornsson A, Saemundsson K, Einarsson P, Tryggvason E, Gronvold K (1977) Current rifting episode in North Iceland. Nature 266:318–323

    Article  Google Scholar 

  • Bjornsson A, Johnsen G, Sigurdsson S, Thorbergsson G, Tryggvason E (1979) Rifting of the plate boundary in North Iceland 1975–1978. J Geophys Res 84(B6):3029–3038

    Google Scholar 

  • Brandsdóttir B (1992) Historical accounts of earthquakes associated with eruptive activity in the Askja volcanic system. Jökull 42:1–12

    Google Scholar 

  • Brandsdottir B, Einarsson P (1979) Seismic activity associated with the September 1977 deflation of the Krafla central volcano in northeastern Iceland. J Volcanol Geotherm Res 6(3–4):197–212

    Article  Google Scholar 

  • Buck WR, Einarsson P, Brandsdottir B (2006) Tectonic stress and magma chamber size as controls on dike propagation: constraints from the 1975–1984 Krafla rifting episode. J Geophys Res-Solid Earth 111(B12):B12404. doi:12410.11029/12005JB003879

    Article  Google Scholar 

  • Bursik M, Sieh K (1989) Range front faulting and volcanism in the Mono Basin, Eastern California. J Geophys Res-Solid Earth and Planets 94(B11):15587–15609

    Article  Google Scholar 

  • Camitz J, Sigmundsson F, Foulger G, Jahn CH, Volksen C, Einarsson P (1995) Plate boundary deformation and continuing deflation of the Askja volcano, North Iceland, determined with GPS, 1987–1993. Bull Volcanol 57(2):136–145

    Google Scholar 

  • de Zeeuw-Van Dalfsen E, Rymer H, Sigmundsson F, Sturkell E (2005) Net gravity decrease at Askja volcano, Iceland: constraints on processes responsible for continuous caldera deflation, 1988–2003. J Volcanol Geotherm Res 139(3–4):227–239

    Article  Google Scholar 

  • Demets C, Gordon RG, Argus DF, Stein S (1994) Effect of recent revisions to the geomagnetic reversal time-scale on estimates of current plate motions. Geophys Res Lett 21(20):2191–2194

    Article  Google Scholar 

  • Einarsson P (1991) Earthquakes and present-day tectonism in Iceland. Tectonophysics 189(1–4):261–279

    Article  Google Scholar 

  • Einarsson P (2008) Plate boundaries, rifts and transforms in Iceland. Jökull 58:35–58

    Google Scholar 

  • Einarsson P, Brandsdottir B (1980) Seismological evidence for lateral magma intrusion during the July 1978 deflation of the Krafla volcano in NE Iceland. J Geophys-Z Geophys 47(1–3):160–165

    Google Scholar 

  • Einarsson P, Sæmundsson K (1987) Earthquake epicenters 1982–1985 and volcanic systems in Iceland (map). In: Sigfússon I (ed) Í hlutarins eðli, Festschrift for Þorbjörn Sigurgeirsson. Menningarsjóður, Reykjavík

    Google Scholar 

  • Einarsson P, Sigmundsson F, Sturkell E, Árnadóttir Þ, Pedersen R, Pagli C, Geirsson H (2006) Geodynamic signals detected by geodetic methods in Iceland. In: Hirt C (ed) Festschrift for Prof. G. Seeber. Wissenschaftliche Arbeiten der Fachrichtung Geodäsie und Geoinformatik der Universität Hannover, Hannover, pp 39–57

    Google Scholar 

  • Gudmundsson A (1995) Ocean-ridge discontinuities in Iceland. J Geol Soc London 152:1011–1015

    Google Scholar 

  • Johnson RW (1989) Volcano distribution and classification. In: Johnson RW (ed) Intraplate volcanism in eastern Australia and New Zealand. Cambridge University Press, Cambridge, pp 7–11

    Google Scholar 

  • Jónsson Ó (1942) Öskjuvatn (in Icelandic). Náttúrufræðingurinn 12:56–72

    Google Scholar 

  • Jónsson Ó (1962) Dyngjufjöll and Askja (in Icelandic). Bókaforlag Odds Björnssonar, Akureyri, pp 1–96

    Google Scholar 

  • Kjartansson G, Thorarinsson S, Einarsson T (1964) C14 datings of quaternary deposits in Iceland. Náttúrufræðingurinn 34:97–160

    Google Scholar 

  • Klein FW, Einarsson P, Wyss M (1973) Microearthquakes on Mid-Atlantic plate boundary on Reykjanes-peninsula in Iceland. J Geophys Res 78(23):5084–5099

    Article  Google Scholar 

  • Klein FW, Einarsson P, Wyss M (1977) Reykjanes peninsula, Iceland, earthquake swarm of september 1972 and its tectonic significance. J Geophys Res 82(5):865–888

    Article  Google Scholar 

  • Knox C (2007) Earthquakes near Askja on the North Iceland plate boundary. Bullard Laboratories, University of Cambridge, Cambridge, pp 1–77

    Google Scholar 

  • La Femina PC, Dixon TH, Malservisi R, Árnadóttir T, Sturkell E, Sigmundsson F, Einarsson P (2005) Geodetic GPS measurements in south Iceland: strain accumulation and partitioning in a propagating ridge system. J Geophys Res 110:B11405. doi:11410.11029/12005JB003675

    Article  Google Scholar 

  • McKenzie D, McKenzie JM, Saunders RS (1992) Dike emplacement on Venus and on Earth. J Geophys Res-Planet 97(E10):15977–15990

    Article  Google Scholar 

  • Okubo CH, Martel SJ (1998) Pit crater formation on Kilauea volcano, Hawaii. J Volcanol Geotherm Res 86(1–4):1–18

    Article  Google Scholar 

  • Opheim JA, Gudmundsson A (1989) Formation and geometry of fractures, and related volcanism, of the Krafla fissure swarm, northeast Iceland. Geol Soc Am Bull 101(12):1608–1622

    Article  Google Scholar 

  • Pagli C, Sigmundsson F, Arnadottir T, Einarsson P, Sturkell E (2006) Deflation of the Askja volcanic system: constraints on the deformation source from combined inversion of satellite radar interferograms and GPS measurements. J Volcanol Geotherm Res 152(1–2):97–108. doi:110.1016/j.jvolgeores.2006.1012.1010

    Article  Google Scholar 

  • Parsons T, Thompson GA (1991) The role of magma overpressure in suppressing earthquakes and topography—worldwide examples. Science 253(5026):1399–1402

    Article  Google Scholar 

  • Pedersen R, Sigmundsson F, Einarsson P (2007) Controlling factors on earthquake swarms associated with magmatic intrusions; Constraints from Iceland. J Volcanol Geotherm Res 162(1–2):73–80

    Article  Google Scholar 

  • Rowland JV, Baker E, Ebinger CJ, Keir D, Kidane T, Biggs J, Hayward N, Wright TJ (2007) Fault growth at a nascent slow-spreading ridge: 2005 Dabbahu rifting episode, Afar. Geophys J Int 171(3):1226–1246. doi:1210.1111/j.1365-1246X.2007.03584.x

    Article  Google Scholar 

  • Ruegg JC, Lepine JC, Tarantola A, Kasser M (1979) Geodetic measurements of rifting associated with a seismo-volcanic crisis in Afar. Geophys Res Lett 6(11):817–820

    Article  Google Scholar 

  • Saemundsson K (1974) Evolution of axial rifting zone in northern Iceland and the Tjornes Fracture Zone. Geol Soc Am Bull 85(4):495–504

    Article  Google Scholar 

  • Saemundsson K (1978) Fissure swarms and Central volcanoes of the neovolcanic zones of Iceland. In: Bowes DR, Leake BE (eds) Geological journal special issue. Seal House, Liverpool, pp 415–432

    Google Scholar 

  • Sæmundsson K (1991) Jarðfræði Kröflukerfisins (in Icelandic). In: Garðarsson A, Einarsson Á (eds) Náttúra Mývatns. Icelandic Nature Sci. Soc, Reykjavík, pp 24–95

    Google Scholar 

  • Sæmundsson K, Jóhannesson H, Grönvold K (2005) Hrúthálsar, a central volcano in Ódáðahraun (in Icelandic). In: Spring conference of the Icelandic Geological Society. The Icelandic Geological Society, Reykjavík

  • Sella GF, Dixon TH, Mao AL (2002) REVEL: a model for recent plate velocities from space geodesy. J Geophys Res-Solid Earth 107(B4):ETG 11. doi:10.1029/2000JB000033

    Article  Google Scholar 

  • Sigurdsson H, Sparks SRJ (1978a) Rifting episode in North Iceland in 1874–1875 and the eruptions of Askja and Sveinagja. Bull Volcanol 41(3):149–167

    Article  Google Scholar 

  • Sigurdsson H, Sparks SRJ (1978b) Lateral magma flow within rifted Icelandic crust. Nature 274(5667):126–130

    Article  Google Scholar 

  • Sigvaldason GE (1979) Rifting, magmatic activity and interaction between acid and basic liquids. The 1875 Askja eruption in Iceland. In: Nordic Volcanological Institute, Report 7903, Reykjavík, pp 1–54

  • Sigvaldason GE (1982) The interaction between water and magma: The Askja eruption in 1875 (in Icelandic). In: Þórarinsdóttir H, Óskarsson ÓH, Steinþórsson S, Einarsson Th (eds) Eldur er í norðri. Sögufélag Reykjavíkur, Reykjavík, pp 37–49

  • Sigvaldason GE, Annertz K, Nilsson M (1992) Effect of glacier loading deloading on volcanism—postglacial volcanic production-rate of the Dyngjufjoll area, central Iceland. Bull Volcanol 54(5):385–392

    Article  Google Scholar 

  • Soosalu H, Einarsson P, Hjartardóttir ÁR, Jakobsdóttir SS, Pedersen R, Sturkell E, White RS (2006) Increased earthquake activity along the divergent plate boundary near the Askja volcano, Iceland. In: The 37th Nordic Seminar on Detection Seismology Nesjavellir, Iceland

  • Soosalu H, White RS, Knox C, Einarsson P, Jakobsdottir S, Key AJ (2009) Lower-crustal earthquakes reflect magma movements beneath the north Iceland rift. Bull Volcanol (in press)

  • Sturkell E, Sigmundsson F (2000) Continuous deflation of the Askja caldera, Iceland, during the 1983–1998 noneruptive period. J Geophys Res-Solid Earth 105(B11):25671–25684

    Article  Google Scholar 

  • Sturkell E, Sigmundsson F, Slunga R (2006a) 1983–2003 decaying rate of deflation at Askja caldera: pressure decrease in an extensive magma plumbing system at a spreading plate boundary. Bull Volcanol 68(7–8):727–735. doi:710.1007/s00445-00005-00046-00441

    Article  Google Scholar 

  • Sturkell E, Einarsson P, Sigmundsson F, Geirsson H, Olafsson H, Pedersen R, de Zeeuw-van Dalfsen E, Linde A, Sacks S, Stefansson R (2006b) Volcano, geodesy and magma dynamics in Iceland. J Volcanol Geotherm Res 150(1–3):14–34. doi:10.1016/j.jvolgeores.2005.1007.1010

    Article  Google Scholar 

  • Tentler T, Mazzoli S (2005) Architecture of normal faults in the rift zone of central north Iceland. J Struct Geol 27(9):1721–1738. doi:1710.1016/j.jsg.2005.1705.1018

    Article  Google Scholar 

  • Thorarinsson S (1971) The age of the light Hekla tephra layers according to corrected C14–datings. Náttúrufræðingurinn 41:99–105

    Google Scholar 

  • Þórarinsson S, Sigvaldason GE (1962) The eruption in Askja, 1961: a preliminary report. Am J Science 260:641–651

    Google Scholar 

  • Þorbjarnardóttir BS, Guðmundsson GB, Hjaltadóttir S, Roberts MJ (2007) Seismicity in Iceland during 2006. Jökull 57:45–59

    Google Scholar 

  • Tilling RI, Dvorak JJ (1993) Anatomy of a basaltic volcano. Nature 363(6425):125–133

    Article  Google Scholar 

  • Tryggvason E (1980) Subsidence events in the Krafla area, north-Iceland, 1975–1979. J Geophys-Z Geophys 47(1–3):141–153

    Google Scholar 

  • Tryggvason E (1989) Ground deformation in Askja, Iceland—its source and possible relation to flow of the mantle plume. J Volcanol Geotherm Res 39(1):61–71

    Article  Google Scholar 

  • Walker GPL (1993) Basaltic-volcano systems. In: Prichard HM, Alabaster T, Harris NBW, Neary CR (eds) Magmatic processes and plate tectonics. Geological Society, London, pp 3–38

    Google Scholar 

  • Wolff-Boenisch D, Gislason SR, Oelkers EH (2006) The effect of crystallinity on dissolution rates and CO2 consumption capacity of silicates. Geochim Cosmochim Acta 70(4):858–870. doi:810.1016/j.gca.2005.1010.1016

    Article  Google Scholar 

  • Wright TJ, Ebinger C, Biggs J, Ayele A, Yirgu G, Keir D, Stork A (2006) Magma-maintained rift segmentation at continental rupture in the 2005 Afar dyking episode. Nature 442(7100):291–294. doi:210.1038/nature04978

    Article  Google Scholar 

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Acknowledgements

We thank Guðmundur E. Sigvaldason, who sadly passed away at early stages of this project, as well as Erik Sturkell and Halldór Ólafsson from the Institute of Earth Sciences, University of Iceland, for their help with the fieldwork and their constructive comments. We would also like to express our gratitude to Kristján Sæmundsson for fruitful discussions. Thanks are due to Rósa Ólafsdóttir from the Institute of Earth Sciences who provided contour lines as well as the outlines of many lava flows in the research area, and Gunnar B. Guðmundsson from the Icelandic Meteorological Office, who provided data on the seismic activity in the area. We are grateful for the help with the ArcInfo software received from Hulda Axelsdóttir, then a student at the University of Iceland, and Bjarki Þór Kjartansson from the Agricultural University of Iceland, who also provided satellite images. Thanks are also due to Bryndís Brandsdóttir, who provided SPOT5 images. We thank V. Acocella and J. Stock for their constructive reviews, and H. Delgado Granados for his editorial help.

This project was supported by the Icelandic Research Fund for Graduate Students (Rannsóknarnámssjóður) and the National Power Company (Landsvirkjun).

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Correspondence to Páll Einarsson.

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Editorial responsibility: H. Delgado Granados

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Figure S1
figure 10

Volcanic fissures (red), tectonic fractures (green) and unclear lineaments (blue) mapped from aerial photographs. (GIF 372 kb)

Figure S2
figure 11

Tectonic fractures and volcanic fissures in the NE subswarm of the Askja fissure swarm. (GIF 526 kb)

High resolution image (TIFF 15376 kb)

High resolution image (TIFF 17664 kb)

Table S1

The width of fractures (in meters) found by inspection on ground in the northeastern subswarm of the Askja fissure swarm, across a given profile. The profile is located east of Mt. Eggert and is perpendicular to the fissure swarm. The area is situated within UTM zone 27. (DOC 38 kb)

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Hjartardóttir, Á.R., Einarsson, P. & Sigurdsson, H. The fissure swarm of the Askja volcanic system along the divergent plate boundary of N Iceland. Bull Volcanol 71, 961 (2009). https://doi.org/10.1007/s00445-009-0282-x

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Keywords

  • Askja volcano
  • Fissure swarm
  • Mid-Atlantic plate boundary
  • Iceland
  • Rift zone
  • Northern volcanic zone
  • Rifting