Misplaced Pages

#499500

18-584: Thordarhyrna central volcano is 15 km (9.3 mi) in diameter, 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. 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. The central volcano Hamarinn of

36-506: A glaciovolcano , is a volcanic form produced by subglacial eruptions or eruptions beneath the surface of a glacier or ice sheet which is then melted into a lake by the rising lava . Today they are most common in Iceland and Antarctica ; older formations of this type are found also in British Columbia and Yukon Territory , Canada . During the eruption, the heat of the lava from

54-485: A height of 1,355 m (4,446 ft) called Pálsfjall. The Thordarhyrna central volcano definitely erupted in a VEI 4 event, on the 28th of May 1903. This was associated with Grímsvötn activity, with the whole dual eruption period of activity extending from December 1902 to January 1904. No other eruption can be assigned with certainty to Thordarhyrna. Similar phreatomagmatic eruptions would erupt disruptive tephra . The following eruptions are likely to have involved

72-482: A large glacial lake outburst flood . The shape of subglacial volcanoes tends to be quite characteristic and unusual, with a flattened top and steep sides supported against collapse by the pressure of the surrounding ice and meltwater. If the volcano eventually melts completely through the ice layer, then horizontal lava flows are deposited, and the top of the volcano assumes a nearly level form. However, if significant amounts of lava are later erupted subaerially , then

90-578: Is found within the Bárðarbunga fissure volcanic system, but is outside the caldera of Bárðarbunga itself. Earthquake swarms associated with the volcano are separate in time and place from other swarms in the Bárðarbunga system. The fissure swarm extending south-west towards Torfajökull has not had recent earthquakes or erupted in the Holocene . A geothermally and seismically active ridge called Lokahryggur or

108-419: 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). 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

126-723: The Grímsvötn Volcano beneath the Vatnajökull ice sheet erupted and caused a Jökulhlaup that affected more than 750 km (290 sq mi) and destroyed or severely damaged several bridges. Sonia Esperanca, program director in the National Science Foundation commented on the danger of subglacial volcanoes: "When an ice-covered volcano erupts, the interplay among molten magma, ice and meltwater can have catastrophic results." In 2008, British Antarctic Survey scientists led by Hugh Corr and David Vaughan, reported (in

144-557: The Djúpá, Hverfisfljót, or Skaftá rivers. There is both a mechanical interaction encouraging dyke propagation between Thordarhyrna, a stratovolcano , and Grímsvötn, despite these volcanoes being relatively far apart, and a close chemical affinity in their lavas. Both volcanoes are part of the Eastern volcanic zone of Iceland , are over the Iceland mantle plume , and are related to two associated parallel fissure systems with crater rows extending to

162-519: The Loki Ridge, extends eastward from Hamarinn under the ice to where in 1996 the Gjálp volcanic fissure erupted between Bárðarbunga and Grímsvötn and produced a large jökulhlaup . The last confirmed eruption was in 1910 when tephra was erupted, but the system may also have had subglacial eruptions in 1986, 1991, 2006, 2008 and 2011. Subglacial volcano A subglacial volcano , also known as

180-515: The Thordarhyrna central volcano: An eruption south of Thordarhyrna in 3550 BC ± 500 years poured out 150,000,000 m (5.3 × 10 cu ft) of lava in the area of Bergvatnsárhraun at the southern edge of Vatnajokull (Djúpárjökull) closest to Thordarhyrna. 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

198-571: The journal Nature Geoscience ) that 2,200 years ago, a volcano erupted under the Antarctica ice sheet (based on airborne survey with radar images). The biggest eruption in Antarctica in the last 10,000 years, the volcanic ash was found deposited on the ice surface under the Hudson Mountains , close to Pine Island Glacier . Many scientists believe that liquid water exists many kilometers below

SECTION 10

#1732851627500

216-478: The north-east, there are the central volcanoes of Hamarinn, Bárðarbunga, and Grímsvötn. These last are tectonically at the north-east corner of the Hreppar microplate . Mostly samples from the Thordarhyrna central volcano are tholeiitic basalt . However samples from the nunataks poking through the ice have yielded basaltic andesite , dacite or rhyolite specimens consistent with more mature lavas. Near Pálsfjall in

234-472: The north-west part of the central volcano, there is a small geothermal area. Hamarinn The Loki-Fögrufjöll ( Icelandic pronunciation: [ˈlɔːcɪ-ˈfœɣrʏˌfjœtl̥] volcanic system; also known as Hamarinn [ˈhaːmarɪn] after its central volcano or Lokahryggur [ˈlɔːkaˌr̥ɪkːʏr̥] ) is a subglacial volcano under the Vatnajökull glacier. The subglacial volcano

252-543: The south east; the 25 km (16 mi) long Laki–Grímsvötn fissure system and the 30 km (19 mi) long Rauðhólar-Eldgígur fissure system. 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

270-502: The subglacial volcano melts the overlying ice. The water quickly cools the lava, resulting in pillow lava shapes similar to those of underwater volcanoes . When the pillow lavas break off and roll down the volcano slopes, pillow breccia , tuff breccia, and hyaloclastite form. The meltwater may be released from below the ice as happened in Iceland in 1996 when the Grímsvötn caldera erupted, melting 3 km of ice and giving rise to

288-455: The surface of Mars, but at this point in time it is impossible to drill to those depths with the rovers in existence. Meredith Payne and Jack Farmer of Arizona State University have studied images from the Viking and Mars Orbiter cameras in search of possible sub-glacial volcanoes that could carry microbes to the surface. It is possible to track catastrophic subglacial volcano eruptions in time with

306-482: The tephra is distinct from tephra assigned with certainty to currently active Icelandic central volcanoes. 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. Jökulhlaups could occur on either the Skeiðarársandur outwash plain or affecting

324-479: The volcano may assume a more conventional shape. In Canada the volcanos have been known to form both conical and nearly level shapes. The more distinctly flat-topped, steep-sided subglacial volcanoes are called tuyas , named after Tuya Butte in northern British Columbia by Canadian geologist Bill Mathews in 1947. In Iceland, such volcanoes are also known as table mountains . Subglacial eruptions often cause jökulhlaups or great floods of water. In November 1996

#499500