![]() Main building of the replica of Stöng, which was buried under volcanic ash from the 1104 eruption During the last 7,000 years, one third of the volcanic ash deposited in Scandinavia, Germany, Ireland, and the United Kingdom originated from Hekla. H 3 and H 4 produced the largest layers of tephra in Iceland since the last ice age. ![]() Hekla 3, 4, and 5 produced huge amounts of rhyolitic ash and tephra, covering 80% of Iceland and providing useful date markers in soil profiles in other parts of Europe such as Orkney, Scandinavia, and elsewhere. Main eruptions in prehistoric times: EruptionĪ Unless otherwise stated eruption dates are from Global Volcanism Program, other sources disagree. Traces of this eruption have been identified in Scottish peat bogs, and in Ireland a study of tree rings dating from this period has shown negligible tree ring growth for a decade. ![]() This would have cooled temperatures in the northern parts of the globe for a few years afterwards. One of the largest Holocene eruptions in Iceland was the Hekla 3 (or H 3) eruption circa 1000 BC, which threw about 7.3 km 3 of volcanic rock into the atmosphere, placing its Volcanic Explosivity Index (VEI) at 5. Hekla beyond a snowy field of volcanic ash Earthquakes in the volcano's vicinity are generally below magnitude 2 while it is dormant and magnitude 3 when erupting. Hekla is closely studied today for parameters such as strain, tilt, deformation and other movement and seismic activity. Hekla is located on the mid-ocean ridge, a diverging plate boundary. When not erupting Hekla is often covered with snow and small glaciers it is also unusually aseismic with activity only starting 30–80 minutes before an eruption. Phenocrysts in Hekla's lava can contain plagioclase, pyroxene, titanomagnetite, olivine, and apatite. It is the only Icelandic volcano to produce calc-alkaline lavas. Hekla's basaltic andesite lava generally has a SiO 2 content of over 54%, compared to the 45–50% of other nearby transitional alkaline basalt eruptions (see TAS classification). The tephra produced by its eruptions is high in fluorine, which is poisonous to animals. This fissure opens along its entire length during major eruptions and is fed by a magma reservoir estimated to have a top 4 km below the surface with centroid 2.5 km lower. Hekla is situated on a long volcanic ridge of which the 5.5 km Heklugjá fissure is considered Hekla proper. The unusual form of Hekla is found on very few volcanoes around the world, notably Callaqui in Chile. Hekla has a morphological type between that of a fissure vent and stratovolcano (built from mixed lava and tephra eruptions) sited at a rift- transform junction in the area where the south Iceland seismic zone and eastern volcanic zone meet. An early Latin source refers to the mountain as Mons Casule. In Icelandic Hekla is the word for a short hooded cloak, which may relate to the frequent cloud cover on the summit. Cumulatively, the volcano has produced one of the largest volumes of lava of any in the world in the last millennium, around 8 km 3. ![]() Approximately 10% of the tephra created in Iceland in the last thousand years has come from Hekla, amounting to 5 km 3. The volcano's frequent large eruptions have covered much of Iceland with tephra, and these layers can be used to date eruptions of Iceland's other volcanoes. Hekla looks rather like an overturned boat, with its keel being a series of craters, two of which are generally the most active. The most active part of this ridge, a fissure about 5.5 km (3.4 mi) long named Heklugjá, is considered to be within Hekla proper. Hekla is part of a volcanic ridge, 40 km (25 mi) long. During the Middle Ages, the Icelandic Norse called the volcano the "Gateway to Hell" and the idea spread over much of Europe. Hekla is one of Iceland's most active volcanoes over 20 eruptions have occurred in and around the volcano since 874. Hekla ( Icelandic pronunciation: ( listen)), or Hecla, is a stratovolcano in the south of Iceland with a height of 1,491 m (4,892 ft). Eggert Ólafsson, Bjarni Pálsson, 20 June 1750
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