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] |
 Geological features near the Thordarhyrna central volcano (red outline). Shading shows: calderas, other central volcanoes , fissure swarms, subglacial terrain above 1,100 m (3,600 ft), seismically active areas between 1995 to 2007. Clicking on the image enables mouse-over with more detail. | |
Geography edit
Thordarhyrna 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 edit
The 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]
Jökulhlaups could occur on either the Skeiðarársandur outwash plain or affecting the Djúpá, Hverfisfljót, or Skaftá rivers.[11]
Geology edit
There is both a mechanical interaction encouraging dyke propagation between Thordarhyrna,[12] a stratovolcano,[13] and Grímsvötn, despite these volcanoes being relatively far apart,[14] and a close chemical affinity in their lavas.[15] Both volcanoes are part of the Eastern volcanic zone of Iceland, are over the Iceland mantle plume,[16] 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.[15][17] 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.[18] 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.[19]
Near Pálsfjall in the north-west part of the central volcano, there is a small geothermal area.[20]
See also edit
References 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
- ^ 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: 1–22. 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.