Bulletin of Volcanology

, 71:961 | Cite as

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

  • Ásta Rut Hjartardóttir
  • Páll Einarsson
  • Haraldur Sigurdsson
Research Article

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.

Keywords

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

Supplementary material

445_2009_282_Fig1_ESM.gif (372 kb)
Figure S1

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

445_2009_282_Fig1_ESM.tif (15 mb)
High resolution image (TIFF 15376 kb)
445_2009_282_Fig2_ESM.gif (527 kb)
Figure S2

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

445_2009_282_Fig2_ESM.tif (17.3 mb)
High resolution image (TIFF 17664 kb)
445_2009_282_MOESM3_ESM.doc (38 kb)
Table S1The 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)

References

  1. 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):189–203CrossRefGoogle Scholar
  2. 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 CrossRefGoogle Scholar
  3. Bjornsson A, Saemundsson K, Einarsson P, Tryggvason E, Gronvold K (1977) Current rifting episode in North Iceland. Nature 266:318–323CrossRefGoogle Scholar
  4. 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):3029–3038Google Scholar
  5. Brandsdóttir B (1992) Historical accounts of earthquakes associated with eruptive activity in the Askja volcanic system. Jökull 42:1–12Google Scholar
  6. 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):197–212CrossRefGoogle Scholar
  7. 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 CrossRefGoogle Scholar
  8. 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):15587–15609CrossRefGoogle Scholar
  9. 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):136–145Google Scholar
  10. 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):227–239CrossRefGoogle Scholar
  11. 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):2191–2194CrossRefGoogle Scholar
  12. Einarsson P (1991) Earthquakes and present-day tectonism in Iceland. Tectonophysics 189(1–4):261–279CrossRefGoogle Scholar
  13. Einarsson P (2008) Plate boundaries, rifts and transforms in Iceland. Jökull 58:35–58Google Scholar
  14. 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):160–165Google Scholar
  15. 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, ReykjavíkGoogle Scholar
  16. 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 39–57Google Scholar
  17. Gudmundsson A (1995) Ocean-ridge discontinuities in Iceland. J Geol Soc London 152:1011–1015Google Scholar
  18. Johnson RW (1989) Volcano distribution and classification. In: Johnson RW (ed) Intraplate volcanism in eastern Australia and New Zealand. Cambridge University Press, Cambridge, pp 7–11Google Scholar
  19. Jónsson Ó (1942) Öskjuvatn (in Icelandic). Náttúrufræðingurinn 12:56–72Google Scholar
  20. Jónsson Ó (1962) Dyngjufjöll and Askja (in Icelandic). Bókaforlag Odds Björnssonar, Akureyri, pp 1–96Google Scholar
  21. Kjartansson G, Thorarinsson S, Einarsson T (1964) C14 datings of quaternary deposits in Iceland. Náttúrufræðingurinn 34:97–160Google Scholar
  22. Klein FW, Einarsson P, Wyss M (1973) Microearthquakes on Mid-Atlantic plate boundary on Reykjanes-peninsula in Iceland. J Geophys Res 78(23):5084–5099CrossRefGoogle Scholar
  23. Klein FW, Einarsson P, Wyss M (1977) Reykjanes peninsula, Iceland, earthquake swarm of september 1972 and its tectonic significance. J Geophys Res 82(5):865–888CrossRefGoogle Scholar
  24. Knox C (2007) Earthquakes near Askja on the North Iceland plate boundary. Bullard Laboratories, University of Cambridge, Cambridge, pp 1–77Google Scholar
  25. 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 CrossRefGoogle Scholar
  26. McKenzie D, McKenzie JM, Saunders RS (1992) Dike emplacement on Venus and on Earth. J Geophys Res-Planet 97(E10):15977–15990CrossRefGoogle Scholar
  27. Okubo CH, Martel SJ (1998) Pit crater formation on Kilauea volcano, Hawaii. J Volcanol Geotherm Res 86(1–4):1–18CrossRefGoogle Scholar
  28. 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):1608–1622CrossRefGoogle Scholar
  29. 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 CrossRefGoogle Scholar
  30. Parsons T, Thompson GA (1991) The role of magma overpressure in suppressing earthquakes and topography—worldwide examples. Science 253(5026):1399–1402CrossRefGoogle Scholar
  31. 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):73–80CrossRefGoogle Scholar
  32. 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 CrossRefGoogle Scholar
  33. 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):817–820CrossRefGoogle Scholar
  34. Saemundsson K (1974) Evolution of axial rifting zone in northern Iceland and the Tjornes Fracture Zone. Geol Soc Am Bull 85(4):495–504CrossRefGoogle Scholar
  35. 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 415–432Google Scholar
  36. Sæmundsson K (1991) Jarðfræði Kröflukerfisins (in Icelandic). In: Garðarsson A, Einarsson Á (eds) Náttúra Mývatns. Icelandic Nature Sci. Soc, Reykjavík, pp 24–95Google Scholar
  37. 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, ReykjavíkGoogle Scholar
  38. 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 CrossRefGoogle Scholar
  39. Sigurdsson H, Sparks SRJ (1978a) Rifting episode in North Iceland in 1874–1875 and the eruptions of Askja and Sveinagja. Bull Volcanol 41(3):149–167CrossRefGoogle Scholar
  40. Sigurdsson H, Sparks SRJ (1978b) Lateral magma flow within rifted Icelandic crust. Nature 274(5667):126–130CrossRefGoogle Scholar
  41. 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 1–54Google Scholar
  42. 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 37–49Google Scholar
  43. 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):385–392CrossRefGoogle Scholar
  44. 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, IcelandGoogle Scholar
  45. 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)Google Scholar
  46. 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):25671–25684CrossRefGoogle Scholar
  47. 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 CrossRefGoogle Scholar
  48. 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 CrossRefGoogle Scholar
  49. 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 CrossRefGoogle Scholar
  50. Thorarinsson S (1971) The age of the light Hekla tephra layers according to corrected C14–datings. Náttúrufræðingurinn 41:99–105Google Scholar
  51. Þórarinsson S, Sigvaldason GE (1962) The eruption in Askja, 1961: a preliminary report. Am J Science 260:641–651Google Scholar
  52. Þorbjarnardóttir BS, Guðmundsson GB, Hjaltadóttir S, Roberts MJ (2007) Seismicity in Iceland during 2006. Jökull 57:45–59Google Scholar
  53. Tilling RI, Dvorak JJ (1993) Anatomy of a basaltic volcano. Nature 363(6425):125–133CrossRefGoogle Scholar
  54. Tryggvason E (1980) Subsidence events in the Krafla area, north-Iceland, 1975–1979. J Geophys-Z Geophys 47(1–3):141–153Google Scholar
  55. 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):61–71CrossRefGoogle Scholar
  56. 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 3–38Google Scholar
  57. 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 CrossRefGoogle Scholar
  58. 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 CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2009

Authors and Affiliations

  • Ásta Rut Hjartardóttir
    • 1
  • Páll Einarsson
    • 1
  • Haraldur Sigurdsson
    • 2
  1. 1.Institute of Earth SciencesUniversity of IcelandReykjavíkIceland
  2. 2.Graduate School of OceanographyUniversity of Rhode IslandNarragansettUSA

Personalised recommendations