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Iceland Volcanoes and Volcanics

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Map, Major Volcanoes of Iceland

The Mid-Atlantic plate boundary passes through Iceland and is reflected in two zones of spreading and volcanism -- an eastern zone, the site of most historical eruptions, and a western zone.

The mostly submarine Vestmannaeyjar volcanic system is the southernmost volcanic center of the eastern volcanic zone that cuts across east-central Iceland. It consists of a roughly 30 x 40 kilometer group of volcanic islands and submarine cones occupying a shallow shelf off the south coast of Iceland.

Bárdarbunga lies beneath the northwest corner of the Vatnajökull ice cap. It is the second highest central volcano in Iceland, with rocks exposed up to 1800 m above sea level. On the basis of historical accounts of eruptions and glacial outbursts, and distinctive chemical characteristics of tephra layers, at least ten tephra-producing eruptions are thought to have taken place beneath the northwest corner of Vatnajökull ice cap during the last 1200 years (Thorarinsson, 1974; Larsen, 1982, 1984; Gudmundsson, 1986). Three eruptions took place on the fissure swarm southwest of Bárdarbunga during the same period. There is not direct evidence that eruptions have taken place withing the Bárdarbunga caldera itself during historical time.

Grimsvötn is situated in the central part of the eastern volcanic zone. A fissure swarm extends 70 kilometers to the southwest. ...

Grimsvötn, together with Bárdarbunga and Kverkfjöll, lie beneath the vast Vatnajökull icecap in east-central Iceland. Due to its subglacial setting and remoteness, the geology of Grimsvötn is poorly known. The volcano has a composite central caldera, of which the southern rim is the only exposed part of the volcano. Only basaltic material is known to have erupted from Grimsvötn. Most known eruptions of Grimsvötn have occurred within the caldera, but the Laki eruption (12 cubic kilometers of basaltic lava) from the fissure swarm 40-70 kilometers southwest of the volcano may also have been fed from a shallow chamber beneath the caldera (Sigurdsson and Sparks, 1978; Sigurdsson, 1983). A large geothermal area in the caldera, with an estimated heat output of 5000 megawatts (Bjornsson, 1974, 1983), continually supplies meltwater to an ice-covered caldera lake. Approximately every 4-10 years the accumulated water is released in glacial outburst floods (jökulhlaups) when the water level is high enough to lift its ice dam (Thorarinsson, 1953; Bjornsson, 1974, 1975; Bjornsson and Kristmannsdottir, 1984). Some jökulhlaups are associated with eruptions. In some instances it can be argued that the extra meltwater g enerated by a subglacial eruption triggered the draining of the caldera lake (for example, during the 1938 eruption). In other cases the sudden pressure release associated with draining may trigger an eruption (Thorarinsson, 1974).

The Vestmannaeyjar islands parallel the structural trend of tectonic fissures (gjár), grabens, and crater rows on the mainland to the north in the eastern volcanic zone. This is a zone of historically active volcanoes, including Hekla, Katla, and the famous Laki fissure eruption of 1783.

The Laki eruption derives its name from a mountain (Laki) which was split by a fissure from which a large volume of lava and gas emanated. ... The Laki eruption produced the largest lava flow on Earth observed in historic times, 2.9 cubic miles of lava which inundated 218 square miles. ...

One of the most destructive volcanic eruptions in the history of Iceland began in the early morning of January 23, 1973, near the Nation's premier fishing port, the town of Vestmannaeyjar (Vést-mun-ayar), on Heimaey (Háme-a-ay), the only inhabited isle in the Vestmannaeyjar volcanic archipelago. ...

MORE 1973 Heimaey Eruption

One of Iceland's most prominent and active volcanoes, Hekla lies near the southern end of the eastern rift zone. Repeated eruptions along this rift are responsible for Hekla's elongated ENE-WSW profile. A 5.5-kilometer-long fissure, Heklugja, cuts across the volcano and is often active along its full length during major eruptions. Frequent large explosive eruptions during historical times have deposited tephra throughout Iceland, providing valuable time markers used to date eruptions from other Icelandic volcanoes. Lava flows from Hekla's historical eruptions, which date back to 1104 A.D., cover much of the volcano's flanks. Hekla's first historical eruption in 1104 was one of the largest in Iceland's recorded history.

Katla volcano, located near the southern end of Iceland's eastern volcanic zone, is hidden beneath the Myrdalsjökull icecap. The subglacial volcano is one of Iceland's most active and is a frequent producer of damaging jökulhlaups, or glacier-outburst floods. A large 11 x 14 kilomters subglacial caldera has been the source of eruptions originating over a wide area, although most historical eruptions have taken place from fissures in the east side of the caldera. These appear to be a continuation of the Eldgja fissure system, which extends more than 57 kilometers to the NE towards Grímsvötn. An eruption from the Eldgja fissure system about 934 AD produced a voluminous lava flow of about 18 cu km, one of the world's largest known Holocene lava flows. Katla has produced frequent subglacial explosive eruptions that have been among the largest tephra-producers in Iceland during historical time.

The Vestmannaeyjar islands parallel the structural trend of tectonic fissures (gjár), grabens, and crater rows on the mainland to the north in the eastern volcanic zone. This is a zone of historically active volcanoes, including Hekla, Katla, and the famous Laki fissure eruption of 1783. The Laki eruption derives its name from a mountain (Laki) which was split by a fissure from which a large volume of lava and gas emanated. ... The Laki eruption produced the largest lava flow on Earth observed in historic times, 2.9 cubic miles of lava which inundated 218 square miles. ...

Among the more prominent theories of events that have triggered global climatic changes and lead to repeated glaciation are: (1) known astronomical variations in the orbital elements of the Earth (the so-called Milankovitch theory); (2) changes in energy output from the Sun; and (3) increases in volcanism that could have thrown more airborne volcanic material into the stratosphere, thereby creating a dust veil and lowered temperatures. ...

The potential climatic effect of the Laki volcanic eruption in Iceland in 1783, the largest effusive (lava) volcanic eruption in historic time, was noted by the diplomat-scientist Benjamin Franklin in 1784, during one of his many sojourns in Paris. Franklin concluded that the introduction of large quantities of volcanic particles into the Earth's upper atmosphere could cause a reduction in surface temperature, because the particles would lessen the amount of solar energy reaching the Earth's surface.

MORE about Volcanoes and the Climate

The mostly submarine Vestmannaeyjar volcanic system is the southernmost volcanic center of the eastern volcanic zone that cuts across east-central Iceland. It consists of a roughly 30 x 40 kilometer group of volcanic islands and submarine cones occupying a shallow shelf off the south coast of Iceland. Vestmannaeyjar was the site of two of Iceland's most noted 20th-century eruptions. The new island of Surtsey grew from the ocean floor during 1963-1967.

Surtsey, Iceland: this 2.5 square kilometer volcanic island lies approximately ' 40 kilometers off the coast of Iceland, and was constructed during the 1963-1967 time period by basaltic eruptions.

The Vatnajökull glacier in Europe is a temperate glacier covering about 8,300 square kilometers in the SE part of Iceland. Volcanic fissure systems of the Mid-Atlantic Ridge plate boundary are partly covered by the western part of the ice sheet. Two major volcanic centers lie beneath the ice, the Bárdarbunga volcanic centre and the Grimsvötn volcanic centre both with large subglacial caldera depressions. The Bárdarbunga centre is a part of a fissure system extending over 100 kilometers to the south and some 50 kilometers to the north of the glacier. The last eruption within the Bárdarbunga centre occurred in 1910, but eruptions on the fissure system have occurred in 871 AD, 1477 AD and 1862 AD, all producing substantial amounts of lava.

The Grimsvötn centre is the more active of the two with an eruption frequency during past centuries close to one eruption per decade. The last eruption occurred in 1983. As Bárdarbunga the Grimsvötn centre is a part of a fissure system which includes the Laki fissure, which in 1783 produced about 12-14 cubic kilometers of basaltic lava. Within the ice filled Grimsvötn caldera intense geothermal activity continuously melts the ice to form a subglacial lake, which at intervals of 5 to 10 years is emptied along subglacial channels to create large floods (jökulhlaup) on the sandur plain, Skeidararsandur, on the Icelandic south coast. The lake was last emptied in 1996 and the water level is presently low.

The present eruption fissure (1996) is located between these two volcanic centres with a direction parallel to the regional tectonic lineament. The subglacial topography directs meltwater from the erupting fissure toward the Grimsvoetn caldera which is rapidly filling. By the evening of Oct. 1st the ice cover above the subglacial lake had risen 10-15 meters. A rise of the water level by additional 35 meters will trigger a flood.

The mostly submarine Vestmannaeyjar volcanic system is the southernmost volcanic center of the eastern volcanic zone that cuts across east-central Iceland. It consists of a roughly 30 x 40 kilometer group of volcanic islands and submarine cones occupying a shallow shelf off the south coast of Iceland. Vestmannaeyjar was the site of two of Iceland's most noted 20th-century eruptions. The new island of Surtsey grew from the ocean floor during 1963-1967. The island of Heimaey, 20 kilometers to the north, was the site of dramatic eruptions in 1973 during which lava flows partially overran the town of Vestmannaeyjar. Several other volcanoes erupted during historical time. Twenty-two postglacial eruption sites are known in the Vestmannaeyjar system.

One of the most destructive volcanic eruptions in the history of Iceland began in the early morning of January 23, 1973, near the Nation's premier fishing port, the town of Vestmannaeyjar, on Heimaey, the only inhabited isle in the Vestmannaeyjar volcanic archipelago.

Both the fishing port and the group of volcanic islands have the same name -- Vestmannaeyjar. In English, Vestmannaeyjar means Westmans' Islands. In Viking times, the Nordic peoples referred to the Irish and other Celtic men as "West" men. Tradition says that the group of volcanic islands, which includes Heimaey and Surtsey, got their name Vestmannaeyjar from escaped Irish (or Celtic) thralls who fled there after killing Hjörleifer Hródmarsson, sworn brother of Ingólfur Arnarson, the first person to permanently settle in Iceland. ...

The 1973 eruption on Heimaey was also the second major eruption (the other being Surtsey) definitely known to have occurred in Vestmannaeyjar since the settlement of Iceland in the ninth century, although there is evidence of a submarine eruption in the archipelago in September 1896. At least 13 offshore (14 including Heimaey) and approximately 125 onshore eruptions have been documented since Iceland's settlement in about A.D. 874. Ten of the 13 offshore eruptions occurred along the submarine Reykjanes Ridge, an extension of the Reykjanes peninsula. This Ridge lies along a parallel fracture system approximately 110 miles west of the northeast-southwest-trending Vestmannaeyjar.

Except for the main island of Heimaey, all the islets in the archipelago are composed of Holocene (geologically recent; that is,less than 10,000 years old) basalts, and, except for Surtsey, the islets are bounded by high sea cliffs and extend out of the sea as a series of stacks. Surtsey has a sandy point to the north and a narrow boulder and cobble beach fringing the rest of the island, including the steep lava cliffs on its windward side and indurated (hard and compacted) tuff on the west. Rocks of Pleistocene age (the span of geologic time from about 3 million to 10,000 years ago) crop out on the north and south parts of the island of Heimaey. These are overlain by younger Holocene basalt flows capped by a prominent volcano, Helgafell, which last erupted 5,000 years ago.

The Vestmannaeyjar islands parallel the structural trend of tectonic fissures (gjár), grabens, and crater rows on the mainland to the north in the eastern volcanic zone. This is a zone of historically active volcanoes, including Hekla, Katla, and the famous Laki fissure eruption of 1783. ... The Laki eruption produced the largest lava flow on Earth observed in historic times, 2.9 cubic miles of lava which inundated 218 square miles.

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