1996 eruption of Gjálp
1996 eruption of Gjálp | |
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Hringvegur partially destroyed | |
Gjálp (Icelandic pronunciation: [ˈcaul̥p]) is a hyaloclastite ridge (tindar) in Iceland under the Vatnajökull glacier shield. Its present form resulted from an eruption series in 1996 and it is probably part of the Grímsvötn volcanic system.[6][7] However not all the scientists were of this opinion, as seismic studies are consistent with a 10 km (6.2 mi) lateral dike intrusion at about 5 km (3.1 mi) depth from Bárðarbunga being the trigger event. This does not exclude a shallower secondary intrusion from Grímsvötn being important in the subaerial eruption itself.[8][a]
Importance
The eruption was of importance, because it was for the first time that a subglacial eruption under a thick ice cover as well as the connected jökulhlaup could be observed and analyzed by modern technique.[10][11]
Geography
Eruption location
The
Vatnajökull ice cap
The
Parts of two volcanic zones of Iceland are placed under Vatnajökull, ie. the very active
The region of the Gjálp fissures is part of this active East Volcanic Zone under Vatnajökull.
Geology
The Gjálp eruption formed in about two weeks a subglacial
The eruption in 1996
Precursors and possible connection between volcanic systems
Some large
Another possibility is that Bárðarbunga magma entered a portion the magmatic system of Grímsvötn and started the eruption by this
Formation of the tindar volcano
The Gjálp
The location is some kilometers to the north of Grímsvötn caldera.[6]
In the beginning, a 2–4 km (1.2–2.5 mi) long N–S trending depression was formed above the fissure, with time three ice cauldrons were built at each end and in the middle,[1] but the eruption concentrated later on one of them where a 200–300 m (660–980 ft) wide crater came to light. After some time, an open ice canyon was built above the fissure. It had a length of about 3.5 km (2.2 mi) and was up to 500 m (1,600 ft) in width.[6]
The meltwater drained first through the ice canyon and then disappeared into subglacial channels and run from there to the subglacial caldera lake of Grímsvötn.[6] The subglacial channels were easily recognized, because continuous melting caused by the hot water from the eruption site initiated the formation of depressions on the ice surface. And so the scientists followed the melting path down to Grímsvötn caldera.[1]
Though the eruption was mostly
During the two weeks of eruption, volcanic activity thawed no less than 3 km3 (0.72 cu mi) of ice, and this continued to a lesser extent for some time after the end of the eruption.[6]
The newly formed tindar disappeared again completely under the glacier ice about 1 year later,[6] but an identifiable ice cauldron remained until at least 2007.[2] The tindar was a 6 km (3.7 mi) long ridge newly deposited to a height of 500 m (1,600 ft) above the pre-existing bedrock with a volume of 0.7 km3 (0.17 cu mi).[2] It is postulated that the original unconsolidated hyaloclastitic volcanic glass and tephra of the ridge could have by now undergone a process called palagonitization due to hydrothermal alteration, to palagonite, a consolidated rock more resistant to erosion, but it is unknown if this has happened.[2]
Eruption products
The eruptive products consisted of predominantly basaltic andesite which surprised the scientists as these more evolved rocks are neither typical for Bárðarbunga nor for Grímsvötn, both more connected to basaltic volcanism. Some scientists thought therefore that Gjálp could be an independent volcano.[12] The bulk samples obtained shortly after the eruption ranged from basaltic andesite to basalt and were of distinctive Grímsvötn composition.[9]: 33 Basaltic andesite from a 1887 eruption had been previously attributed to the Grímsvötn volcanic system and had very similar composition.[9] Tephra assigned to the eruption has been analysed by several researchers and has composition that is Grímsvötn basaltic andesite with rarely Grímsvötn basalt. A total of three samples out of the several hundred in the literature had some tephra with Bárðarbunga basalt composition. It is unknown if this was due to contamination from pre-existing tephra layers in the ice that was overlying Gjálp or if the Bárðarbunga basalt was erupted together with the Grímsvötn basaltic andesite.[9]: 62
Jökulhlaup in 1996
In the beginning, scientists presumed that the eruption would be followed immediately by a big jökulhlaup (sort of a meltwater tsunami including large blocks of ice and a high quantity of sediment). But it took some time to fill the subglacial lake of Grímsvötn in such a manner that the ice wall holding it back would break.[6]
Not before some weeks had passed after the eruption was terminated, the expected jökulhlaup took place from 4 to 7 November 1996.
In the end, the water sprang up from under the glacier edge and the flood covered most of
The volume of meltwater produced by this eruption was around 4 km3.
Former eruption in 1938
At more or less the same place another eruption had taken place in the 1930s. It had also caused a jökulhlaup, but at the time, science could not yet analyse the events. That eruption stayed subglacial.[6]
See also
- List of volcanic eruptions in Iceland
- Subglacial volcano
- Grímsvötn
- Subglacial eruption
- Bárðarbunga
- Ice cauldron
Further reading
- Helgi Björnsson: Subglacial lakes and jökulhlaups in Iceland. Global and Planetary Change 35 (2002) 255–271 Archived 31 July 2021 at the Wayback Machine
Notes
- ^ Despite the extensive study the precise sequence of events during the eruption has not been conclusively determined as well as assignment to volcanic system. Several authorities have speculated on the following sequence of events given evolving volcanology theory in the last decade:[9]: 62
- Deep basaltic primary intrusion from Bárðarbunga system on 29th September 1996
- This intercepted a maturing Grímsvötn magma pocket (that may have had some active Grímsvötn basalt magma input at the time)
- Which was triggered into eruption 30th September 1996 onwards
- Tectonic interaction along a fault that propagated from Bárðarbunga towards Grímsvötn
- This intercepted an almost primed maturing Grímsvötn magma pocket (that may have had some active Grímsvötn basalt magma input at the time)
- Which was triggered into eruption 30th September 1996 onwards
- Subglacial eruption at north western part of Bárðarbunga Caldera on 29th September 1996
- Deep basaltic Bárðarbunga intrusion on far side of Bárðarbunga system into maturing shallower magma pocket shared with Grímsvötn system
- Which was triggered into eruption 30th September 1996 onwards
- Maturing shallow magma pocket in either Bárðarbunga volcanic system or its Loki-Fögrufjöll subsystem (best location data on 192 peri-eruption seismic events with good location solutions only assigned two to Loki Ridge, but perhaps there is a magma pocket under the Loki Ridge)
- Bárðarbunga Caldera priming event 29th September 1996
- Bárðarbunga volcanic system triggered into subaerial eruption 30th September 1996 onwards
References
- ^ . Retrieved 8 August 2020.
- ^ .
- ^ "Grímsvötn". Global Volcanism Program. Smithsonian Institution.
- ^ a b Björnsson, H.; Einarsson, P. (1990). "Volcanoes beneath Vatnajökull, Iceland: Evidence from radio echo-sounding, earthquakes and jökulhlaups" (PDF). Jökull. 40: 147–168. Archived (PDF) from the original on 20 March 2023. Retrieved 25 March 2024.: 155
- ^ a b Jakobsdóttir, S.S. (2008). "Seismicity in Iceland: 1994–2007" (PDF). Jökull. 58 (1): 75–100.: 87
- ^ a b c d e f g h i j k Snæbjörn Guðmundsson: Vegavísir um jarðfræði Íslands. Reykjavík 2015, p. 280-281
- ^ See also "Grímsvötn:Eruptive history". Global Volcanism Program. Smithsonian Institution. Retrieved 29 August 2020.
- ^ .
- ^ a b c d Jóngeirsdóttir, Irma Gná (2022). The tephra layer formed in the 1996 eruption of Gjálp: Dispersal and volume. Magister Scientiarum thesis (Thesis). Faculty of Earth Science School of Engineering and Natural Sciences, University of Iceland.
- .
- . Retrieved 30 August 2020.
- ^ . Retrieved 29 August 2020.
- ^ hdl:11568/500513. Retrieved 8 August 2020.
- ^ Thordarson, Thorvaldur; Höskuldsson, Ármann (2008). "Postglacial volcanism in Iceland" (PDF). Jökull. 58. Retrieved 24 March 2024.
- ^ a b Friðriksdóttir, Hildur María (2017). Landris á Vatnajökulssvæðinu metið með GPS landmælingum. BS ritgerð (PDF) (Thesis) (in Icelandic). Jarðvísindadeild Háskóli Íslands. Leiðbeinendur Sigrún Hreinsdóttir, Erik Sturkell. Retrieved 24 March 2024.
- . Retrieved 31 August 2020.
- ^ See also: Björnsson, Helgi; Einarsson, Páll (1990). "Volcanoes beneath Vatnajökull, Iceland. Evidence from radio echo sounding, earthquakes and jökulhlaups". Jökull. 40. Retrieved 8 August 2020.
- hdl:11568/500303. Retrieved 4 September 2020.
- ^ Utami, I.W. (2018). A reappraisal of seismicity recorded during the 1996 Gjalp eruption in Iceland using modern seismological methods. PhD dissertation (PDF) (Thesis) (in Chinese). National Central University, Taiwan (國立中央大學). Retrieved 24 March 2024.
- .
- ^ Jóhannesson, Tomas (2002). "Propagation of a subglacial flood wave during the initiation of a jôkulhlaup". Hydrological Sciences-Journal-des Sciences Hydrologiques. 47 (3). Retrieved 8 August 2020.
- ^ See also: Björnsson, Helgi (2010). "Understanding jökulhlaups: from tale to theory" (PDF). Journal of Glaciology. 56 (200). Retrieved 8 August 2020.
- ^ M.T. Gudmundsson, G. Larsen, Á. Höskuldsson and Á.G. Gylfason: Volcanic hazards in Iceland. Jökull no. 58 (2008) (PDF) Retrieved 8 August 2020.