Thordarhyrna (Icelandic: Þórðarhyrna [ˈθourðarˌhɪ(r)tna] ) is one of seven[3] subglacial volcanoes beneath the Vatnajokull glacier in Iceland. It is a paired active central volcano with Grímsvötn, and can be classified as part of the Grímsvötn-Laki volcanic system, with common fissure swarms to the south.[4]
| Thordarhyrna | |
|---|---|
| Þórðarhyrna | |
| Highest point | |
| Elevation | 1,650 m (5,410 ft)[1] |
| Listing | List of volcanoes in Iceland |
| Coordinates | 64°12′4″N 17°0′17″W / 64.20111°N 17.00472°W |
| Geography | |
  Thordarhyrna | |
| Geology | |
| Mountain type | Subglacial volcano/Icelandic stratovolcano |
| Last eruption | 1904[2] |
 Selected geological features near the Thordarhyrna central volcano and Grímsvötn volcanic system (red outlines). Other shading shows: calderas, central volcanoes and fissure swarms, subglacial terrain above 1,100 m (3,600 ft), and seismically active areas. Clicking on the image enlarges to full window and enables mouse-over with more detail. | |
Geography
editThordarhyrna central volcano is 15 km (9.3 mi) in diameter,[5] and located north-east of the Síðujökull outlet glacier in a line that goes through the Háabunga ice cap feature of Vatnajokull on the way to the Grímsvötn caldera.[6] To the immediate south-east of Thordarhyrna the outlet glacier has been called Djúpárjökull and to its east the outlet glacier has been called Grænalónsjökull.[7] The central volcano Hamarinn of the Bárðarbunga volcanic system is to the north-east.
Most of the volcano is covered with between 100–600 m (330–1,970 ft) of ice and its highest point is about 1,650 m (5,410 ft). [4][1] It is to the south-east of a higher ice covered ridge connecting it with Grímsvötn called Háabunga which reaches a height of 1,742 m (5,715 ft). The eastern flank of the volcano has an ice free area with a height of 1,355 m (4,446 ft) called Pálsfjall.[6]
Eruptions
editThe Thordarhyrna central volcano definitely erupted in a VEI 4 event, on the 28th of May 1903.[2] This was associated with Grímsvötn activity, with the whole dual eruption period of activity extending from December 1902 to January 1904.[2] No other eruption can be assigned with certainty to Thordarhyrna.[8] Similar phreatomagmatic eruptions would erupt disruptive tephra.[9]
The following eruptions are likely to have involved the Thordarhyrna central volcano:
- 15 August 1887 - 1889 with a VEI 2 event[2]
- 4 February 1823 with a VEI 2 event[2]
- 1753 with jökulhlaups in the rivers to the south-west side of Thordarhyrna.[8]
An eruption south of Thordarhyrna in 3550 BC ± 500 years poured out 150,000,000 m3 (5.3×109 cu ft) of lava in the area of Bergvatnsárhraun at the southern edge of Vatnajokull (Djúpárjökull) closest to Thordarhyrna.[10]
The Borrobol tephra, which are believed to have an Icelandic origin, have been identified from Greenland, through to Scotland and Sweden and has layers dated from 16.65 to 12.77 BP, but the tephra is distinct from tephra assigned with certainty to currently active Icelandic central volcanoes.[11] Greenland high resolution ice-core studies on tephra samples erupted on two occasions dated as 14,308 ± 177 BP and 14,202 ± 173 BP showed a similar composition to non-tephra samples from three nunataks of Thordarhyrna.[12]
Jökulhlaups could occur on either the Skeiðarársandur outwash plain or affecting the Djúpá, Hverfisfljót, or Skaftá rivers.[13]
Geology
editThere is both a mechanical interaction encouraging dyke propagation between Thordarhyrna,[14] a stratovolcano,[15] and Grímsvötn, despite these volcanoes being relatively far apart,[16] and a close chemical affinity in their lavas.[17] Both volcanoes are part of the Eastern volcanic zone of Iceland, are over the Iceland mantle plume,[18] and are related to two associated parallel fissure systems with crater rows extending to the south east; the 25 km (16 mi) long Laki–Grímsvötn fissure system and the 30 km (19 mi) long Rauðhólar-Eldgígur fissure system.[17][19] The 1783 Laki fissure eruption crater row is the location of the most significant effusive eruption in the last 1000 years in Iceland.
A fault runs (N 35° W) from Thordarhyrna towards Hamarinn, and separates two different tectonic regions. The southern topography has north-east to south-west long linear hyaloclastic ridges, while to the north-east, there are the central volcanoes of Hamarinn, Bárðarbunga, and Grímsvötn.[20] These last are tectonically at the north-east corner of the Hreppar microplate.
Mostly samples from the Thordarhyrna central volcano are tholeiitic basalt.[5] However samples from the nunataks poking through the ice have yielded basaltic andesite, dacite or rhyolite specimens consistent with more mature lavas.[21]
Near Pálsfjall in the north-west part of the central volcano, there is a small geothermal area.[22]
See also
editReferences
edit- ^ a b Guðmundsson & Larsen 2019, Central Volcano.
- ^ a b c d e "Thordarhyrna". Global Volcanism Program. Smithsonian Institution. Retrieved 31 March 2024.: Eruptive History
- ^ Andrew 2008, Figure 2.8.
- ^ a b Guðmundsson & Larsen 2019, Short Description.
- ^ a b Guðmundsson & Larsen 2019, Detailed Description:1. Geological setting and tectonic context.
- ^ a b "National land survey of Iceland (Kortasja)". Retrieved 30 March 2024.
- ^ Magnússon et al. 2005, fig. 3.
- ^ a b Guðmundsson & Larsen 2019, Detailed Description:4. Eruption history and pattern.
- ^ Guðmundsson & Larsen 2019, Detailed Description:7. Erupted material & Grain size distribution.
- ^ "Grimsvötn". Global Volcanism Program. Smithsonian Institution. Retrieved 31 March 2024.: Eruptive History
- ^ Lind, E.M.; Lilja, C.; Wastegård, S.; Pearce, N.J. (2016). "Revisiting the Borrobol Tephra". Boreas. 45 (4): 629–643. doi:10.1111/bor.12176. ISSN 0300-9483.: 629, 632, 643
- ^ Cook, E.; Davies, S.M.; Guðmundsdóttir, E.R.; Abbott, P.M.; Pearce, N.J. (2018). "First identification and characterization of Borrobol-type tephra in the Greenland ice cores: new deposits and improved age estimates". Journal of Quaternary Science. 33 (2): 212–224. doi:10.1002/jqs.3016. hdl:20.500.11815/675. ISSN 0267-8179. PMID 29576671.: 215–216
- ^ Guðmundsson & Larsen 2019, Detailed Description:8. Volcanic hazards.
- ^ Gudmundsson & Andrew 2007, 4. Mechanical Interaction.
- ^ "Thordarhyrna". Global Volcanism Program. Smithsonian Institution. Retrieved 31 March 2024.
- ^ Andrew & Gudmundsson 2008, 7. Discussion and conclusions.
- ^ a b Manning & Thirlwall 2014, p. 958.
- ^ Andrew & Gudmundsson 2008, 4. Mechanical interaction.
- ^ Guðmundsson & Larsen 2019, Detailed Description:2. Morphology and topography.
- ^ Bjornsson 1986, p. 15.
- ^ Gudmundsson, M. T.; Larsen, G. (2019). "Grímsvötn Alternative name: Grímsvötn-Laki". Retrieved 1 April 2024.: Detailed Description:1. Geological setting and tectonic context
- ^ Guðmundsson & Larsen 2019, Detailed Description:5. Characteristics during non-eruptive periods.
Sources
edit- Andrew, Ruth Ella Beatrice (2008). Volcanotectonic Evolution and Characteristic Volcanism of the Neovolcanic Zone of Iceland. PhD thesis (PDF) (Thesis). University of Göttingen. Archived from the original (PDF) on 2012-03-09. Retrieved 2011-05-24.
- Gudmundsson, A.; Andrew, R.E. (2007). "Mechanical interaction between active volcanoes in Iceland". Geophysical Research Letters. 34 (10): L10310. Bibcode:2007GeoRL..3410310G. doi:10.1029/2007GL029873.
- Andrew, Ruth E. B.; Gudmundsson, Agust (20 November 2008). "Volcanoes as elastic inclusions: their effects on the propagation of dykes, volcanic fissures, and volcanic zones in Iceland". Journal of Volcanology and Geothermal Research. Volcanic Flows and Falls. 177 (4). Elsevier: 1045–1054. doi:10.1016/j.jvolgeores.2008.07.025.
- Guðmundsson, Magnús T.; Larsen, Guðrún (2019). "Þórðarhyrna central volcano (Grímsvötn-Laki volcanic system) e: Thordarhyrna". Retrieved 31 March 2024.
- Bjornsson, H. (1986). "Surface and bedrock topography of ice caps in Iceland, mapped by radio echo-sounding". Annals of Glaciology. 8: 11–18. doi:10.3189/S026030550000104X.
- Manning, C.J.; Thirlwall, M.F. (2014). "Isotopic evidence for interaction between Öræfajökull mantle and the Eastern Rift Zone, Iceland". Contributions to Mineralogy and Petrology. 167 (1): 1–22. Bibcode:2014CoMP..167..959M. doi:10.1007/s00410-013-0959-1.
- Magnússon, E.; Björnsson, H.; Dall, J.; Pálsson, F. (2005). "The 20th century retreat of ice caps in Iceland derived from airborne SAR: W-Vatnajökull and N-Mýrdalsjökull". Earth and Planetary Science Letters. 237 (3–4): 508–515. Bibcode:2005E&PSL.237..508M. doi:10.1016/j.epsl.2005.06.038.