Hekla
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| Hekla | |
|---|---|
 July 2005: Hekla beyond a field of volcanic ash |
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| Elevation | 1,488 metres (4,881 feet) |
| Location | Iceland |
| Coordinates | |
| Type | Stratovolcano |
| Last eruption | February 28, 2000 |
Hekla is a volcano located in the south of Iceland at , with a height of 1,488 m (4,881 ft). Hekla is Iceland's most active volcano; over 20 outbreaks having occurred in and around the volcano since 874. During the Middle Ages, Icelanders called the volcano the "Gateway to Hell."
Hekla is part of a volcanic ridge, 40 km (25 mi) long. However, the most active part of this ridge, about 5.5 km (3.4 mi) long, is considered to be the volcano Hekla proper. Looking rather like an overturned boat, with its keel being in fact a series of craters, two of which are generally the most active.
Hekla is not only unusually shaped for a stratovolcano, but it is also unusual in having produced mostly basaltic andesite rather than basalt, which is the case in most volcanoes in Iceland. It has also produced even more silicic rock types, including rhyodacite during some of its largest eruptions.
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[edit] Famous eruptions
The earliest recorded eruption of Hekla took place in 1104, although very likely there had been many more during the time of Viking settlement. The 1104 eruption was one of Hekla's largest known, ejecting 2.5 cubic km of tephra.
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. Hekla took a long rest of more than sixty years duration prior to 1845, when it suddenly burst forth on September 2 (Anonymous, 1872):
- After a violent storm on the night of the 2nd of September in that year, the surface of the ground in the Orkney Islands was found strown with volcanic dust. There was thus conveyed to the inhabitants of Great Britain an intimation that Hecla [sic] had been again at work. Accordingly, tidings soon after arrived of a great eruption of the mountain. On the night of the 1st of September, the dwellers in its neighbourhood were terrified by a fearful underground groaning, which continued till mid-day on the 2nd. Then, with a tremendous crash, there were formed in the sides of the cone two large openings, whence there gushed torrents of lava, which flowed down two gorges on the flanks of the mountain. The whole summit was enveloped in clouds of vapour and volcanic dust. The neighbouring rivers became so hot as to kill the fish, and the sheep fled in terror from the adjoining heaths, some being burnt before they could escape.
- On the night of the 15th of September, two new openings were formed — one on the eastern, and the other on the southern slope — from both of which lava was discharged for twenty-two hours. It flowed to a distance of upwards of twenty miles, killing many cattle and destroying a large tract of pasturage. Twelve miles from the crater, the lava-stream was between forty and fifty feet deep and nearly a mile in width. On the 12th of October a fresh torrent of lava burst forth, and heaped up another similar mass. The mountain continued in a state of activity up to April 1846; then it rested for a while, and began again in the following month of October. Since then, however, it has enjoyed repose.
- The effects of these eruptions were disastrous. The whole island was strown with volcanic ash, which, where they did not smother the grass outright, gave it a poisonous taint. The cattle that ate of it were attacked by a murrain, of which great numbers died. The ice and snow, which had gathered about the mountain for a long period of time, were wholly melted by the heat. Masses of pumice weighing nearly half a ton were thrown to a distance of between four and five miles.
Eruptions in Hekla are extremely 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 March 29, 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 (Þórarinsson, 1967).
The most recent eruption was on February 26, 2000. During this eruption, a NASA DC-8 aeroplane acidentally flew through the plume with all instruments switched on, resulting in unprecedented measurement of a young volcanic plume.
Report on this last eruption in January 2003: Up until now, it has always been assumed that Hekla was incapable of producing the most dangerous of volcanic phenomena, the pyroclastic flow. Now, however, a team from the Norvol Institute in Reykjavík, under the leadership of Dr. Ármann Höskuldsson, has reported that they have found traces of a pyroclastic flow, roughly 5 km long, stretching down the side of the mountain. This will call for a reappraisal of volcanic eruptions of the basic rock type, which up to now were generally thought not to produce large pyroclastic flows. It will also require that the public and curious spectators who always rush to the scene at the start of a new outbreak, to be kept much further away from the volcanic activity than was thought necessary during previous outbreaks.
[edit] Historical and prehistoric eruptions
This volcano erupted in 2000, 1991, 1980, 1970, 1947, 1845, 1766, 1693, 1636, 1597, 1510, 1434, 1389, 1341, 1300, 1222, 1206, 1158 and 1104.
One of the most largest Holocene eruptions was the H3 eruption of 950 BC which threw about 7.3 cubic km[1] of volcanic rock into the atmosphere and very likely caused cooling of global temperatures for a few years afterwards.
Main eruptions in prehistoric times:
[edit] Miscellaneous
- In 2006, Australian world/fusion band Umanee recorded and published instrumental song titled Mount Hekla performed by drums, cello and hurdy-gurdy.[2]
- Hecla was the name of a Carmarthen and Cardigan Railway steam locomotive built in 1864.
[edit] See also
[edit] References
- Anonymous, (1872), Wonders of Creation: A descriptive account of volcanoes and their phenomena, e-text No. 6131, Project Gutenburg (accessed 28 November 2006)
- Hutchinson, I.P., (1983), Upphaf Eldgossins í Heklu, 1980 (On the Eruption of Hekla, 1980). Náttúrufræðingurinn, 52 (1–4), p. 175–183. (In Icelandic and English)
- Þórarinsson, S., (1967), The eruption of Hekla in historical times. Vol. I: The eruption of Hekla 1947–48, Soc. Sci. Islandica, p. 1–183
