Hekla
| Hekla | |
|---|---|
 Hekla and Þjórsá | |
| Highest point | |
| Elevation | 1,488 m (4,882 ft) |
| Prominence | 755 m (2,477 ft)  |
| Coordinates | 63°59′32″N 19°39′57″W / 63.99222°N 19.66583°WCoordinates: 63°59′32″N 19°39′57″W / 63.99222°N 19.66583°W |
| Naming | |
| English translation | Hooded |
| Language of name | Icelandic |
| Geography | |
  Hekla Iceland | |
| Geology | |
| Mountain type | Active fissure stratovolcano |
| Last eruption | February to March 2000 |
| Climbing | |
| First ascent | Eggert Ólafsson, Bjarni Pálsson, 20 June 1750[1] |
Hekla (Icelandic pronunciation: [ˈhɛhkla] (
listen)), or Hecla,[2][3] is a stratovolcano in the south of Iceland with a height of 1,491 m (4,892 ft). Hekla is one of Iceland's most active volcanoes; over 20 eruptions have occurred in and around the volcano since 874. During the Middle Ages, Europeans called the volcano the "Gateway to Hell".
Hekla is part of a volcanic ridge, 40 km (25 mi) long. The most active part of this ridge, a fissure about 5.5 km (3.4 mi) long named Heklugjá [ˈhɛhklʏˌcauː], is considered to be within Hekla proper. Hekla looks rather like an overturned boat, with its keel being a series of craters, two of which are generally the most active.[4][5]
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. Approximately 10% of the tephra created in Iceland in the last thousand years has come from Hekla, amounting to 5 km3. Cumulatively, the volcano has produced one of the largest volumes of lava of any in the world in the last millennium, around 8 km3.
Etymology[edit]
In Icelandic Hekla is the word for a short hooded cloak, which may relate to the frequent cloud cover on the summit. An early Latin source refers to the mountain as Mons Casule.[6]
Reputation[edit]
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After the eruption of 1104, stories, probably spread deliberately through Europe by Cistercian monks, told that Hekla was the gateway to Hell.[7] The Cistercian monk Herbert of Clairvaux wrote in his De Miraculis (without naming Hekla):
The renowned fiery cauldron of Sicily, which men call Hell's chimney ... that cauldron is affirmed to be like a small furnace compared to this enormous inferno.[8]
— Herbert of Clairvaux, Liber De Miraculis, 1180
A poem by the monk Benedeit from circa 1120 about the voyages of Saint Brendan mentions Hekla as the prison of Judas.
In the Flatey Book Annal it was recorded that during the 1341 eruption, people saw large and small birds flying in the mountain's fire which were taken to be souls.[9] In the 16th century Caspar Peucer wrote that the Gates of Hell could be found in "the bottomless abyss of Hekla Fell". The belief that Hekla was the gate to Hell persisted until the 19th century.[8] There is still a legend that witches gather on Hekla during Easter.[10]
Geology[edit]
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. The unusual form of Hekla is found on very few volcanoes around the world, notably Callaqui in Chile.[11] Hekla is situated on a long volcanic ridge of which the 5.5 km Heklugjá fissure is considered Hekla proper. 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. The tephra produced by its eruptions is high in fluorine, which is poisonous to animals. Hekla's basaltic andesite lava generally has a SiO2 content of over 54%, compared to the 45–50% of other nearby transitional alkaline basalt eruptions (see TAS classification).[12][13][14][15] It is the only Icelandic volcano to produce calc-alkaline lavas.[16] Phenocrysts in Hekla's lava can contain plagioclase, pyroxene, titanomagnetite, olivine, and apatite.[17]
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.[18] Hekla is located on the mid-ocean ridge, a diverging plate boundary. Hekla is closely studied today for parameters such as strain, tilt, deformation and other movement and seismic activity.[13] Earthquakes in the volcano's vicinity are generally below magnitude 2 while it is dormant and magnitude 3 when erupting.[18]
Eruption history[edit]
The earliest recorded eruption of Hekla took place in 1104. Since then there have been between twenty and thirty considerable eruptions, with the mountain sometimes remaining active for periods of six years with little pause. Eruptions in Hekla are varied and difficult to predict. Some are very short (a week to ten days) whereas others can stretch into months and years (the 1947 eruption started 29 March 1947 and ended April 1948). But there is a general correlation: the longer Hekla goes dormant, the larger and more catastrophic its opening eruption will be.[19] The most recent eruption was on 26 February 2000.
Prehistoric eruptions[edit]
One of the largest Holocene eruptions in Iceland was the Hekla 3 (or H3) eruption circa 1000 BC,[20][21] which threw about 7.3 km3[14] of volcanic rock into the atmosphere, placing its Volcanic Explosivity Index (VEI) at 5. This would have cooled temperatures in the northern parts of the globe for a few years afterwards. 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.[21]
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