1158: This eruption is believed to be responsible for the formation of the Efrahvolshraun lava flow on the west side of Hekla.
1206: Small scale eruption where tephra was sent in a northeasterly direction.
1222: Another small eruption similar to the one in 1206.
1300: Large eruption lasting the whole year; the second largest tephra eruption in Iceland's history. The southern Selsundshraun lava flow probably formed in this eruption.
1341: Medium size eruption that ejected tephra that was carried to the west and southwest of Hekla, poisoning a large number of livestock most likely by fluorine.
1389: This eruption was responsible for the Nordurhraun or northern Selsundshraun lava flow.
1440: Uncertian eruption might have occurred southeast of Hekla at Raudoldur.
1510: Starting out very violently sending stones flying up to 25 miles (40 km) away; one such rocks hit and killed a man in Landsveit, Iceland.Considerable tephra damage to the southwest.
1554: Poorly documented eruption occurred southwest of Hekla at Raudubjallar.
1597: Similar to the 1947 eruption and lasting over six months.
1636: Small scale eruption that lasted over a year causing extensive mortality to local livestock.
1693: Starting out very violently Hekla produced nearly 60,000 cu. meters of tephra per second. This eruption event lasted for at least 7 months causing great numbers of wildlife and livestock to die off from fluorine poisoning or starvation. A considerable lava flow was associated with this event, which also ejected fine ash high enough for it to be carried all the way to Norway.
1725: A poorly documented eruption occurred to the south, southwest and east of Helka.
1766: The largest Hekla eruption in historical times occurred 3:30 in the morning April 5th and continued until May of 1768. This was Iceland's largest lava eruption in historical times. Lava reportedly flowed out from the fissure in all directions although mostly to the southwest. Tephra fell to a thickness of an inch to an inch and a half (2-4 cm) in some areas. Livestock and wildlife populations experienced a huge die-off. Some lava bombs measuring a foot and a half in diameter (1/2 meter) were found 9-12 miles (15-20 km) away. Flooding was also associated with this eruption when ice and snow melted from Heklašs slopes.
1845: This eruption lasted over seven months. In the first four hours tephra was ejected at a rate of about 20,000 cu. meters per second; fine ash was found as far as the Shetland Islands and Scotland. Ash and pumice fell over farm and grazing lands causing livestock and wildlife to die. The lava flow associated with this eruption flowed mainly west-north-west.
1878: An explosive eruption occurred to the east of Helka at Krakagigar that produced lava.
1913: Explosive eruptions occurred to the east and northeast of Hekla at Mundafit and Lambafit. Those eruption events also produced lava flows.
1947: A hundred years went by without a rumbling from Heklašs depths, then on Saturday, March 29th at about 6:41 in the morning an eruption cloud consisting mainly of water vapor rose to a height of 19 miles (98,000 ft. or 30,000 m) into the sky within ten minutes. Within the first half hour lava began to well up in the fissure and poured over and down Heklašs south-eastern slopes at a rate of about 3,500 cu. meters of lava per second. By the end of the day, lava was rushing out of both ends of the fissure. Great clouds of steam bellowed from Heklašs western slope where floods had originated from what had been ice and snow fields. Eight separate eruption columns were visible by the second day and at the lower end of the fissure a crater had opened up and from it streamed an enormous river of lava. This crater was given the name Hraungigur (Lava Crater). Another two large craters had also formed, an explosion crater on the southwest slope named Axlargigur (Shoulder Crater) and a summit crater named Toppgigur. This eruption continued until mid-April of the next year and over this time grew 184 ft. (56 meters) to a elevation of 4,930 ft. (1,503 m).
1980: On the 17th of August Helka started erupting explosively first from the summit area and then spead along the whole 4.3 mile (7 km) fissure. The eruption column of steam and then dark tephra reached an altitude of over 49,000 ft.(15 km). The maximum tephra thinkness for this eruption was reported ~6 miles (10 km) north of the summit with a depth of 8 inches (20 cm). The fluorine content in the tephra was high enough to cause heath problems with livestock. Lava started to flowing from the summit of Helka and continued along the length of the fissure, all together forming four seperate flows. The largest amount of lava was erupted within the first twelve hours and and by August 20th the only activity left was eruptions of steam.
1981:The event that occurred on April 9th started out with explosive eruptions of ash, some columns extended as high as 21,648 ft. (6.6 km) above sea level. Shortly after the explosive events lava began flowing from a new crater that had been formed at Helka's summit. Three main flows originated here, the largest two flowed down Helka's northern slope and the smaller down its southern face. This eruption is thought to be a continuation of Helka's 1980 eruption.
1991: On January 17th Helka violently erupted with a cloud of ash and tephra that reached an altitude of 39,360 ft. (12 km). During this eruption a summit fissure and a main crater were created and from these lava flows extended down the southeastern and northwestern slopes. Lava fountains in these craters reached a height of 984 ft. (300m). This eruption continued until March 11th when activity once again died down.
Bahn,Paul G. 1993,Volcanoes: Fire from the Earth, Harry N.Abrams, Inc., New York p.41.
Bullard, F. M. 1976, Volcanoes of the Earth, Univ. of Texas Press
Gronvold,K. 1994, Bullitin of Volcanic Eruptions No.31: Annual report of the world volcanic eruptions in 1991, Volc. Society of Japan, Tokyo & IAVCEI IUGG, p.123.
Jakobsson, Sveinn P. 1979, Acta Naturalia Islandica #26: Petrology of Recent basalts of the Eastern Volcanic Zone, Iceland, Icelandic Museum of Natural History, Reykjavik p.18
McClelland, L.;T.Simkin, M. Summers, E. Nielsen, T.C. Stein; eds. 1989 Global Volcanism 1975-1985, Prentice-Hall, Inc. New Jersey
Thorarinsson, Sigurdur 1970, Hekla: A Notorious Volcano, Almenna Bokafelagid, Reykjavik
Wood, C.A.; J.L. Whiteford-Stark; J.W. Head 1977 Iceland Field Itinerary: Basaltic Volcanism Study Project, Team 5; Lunar Science Institute, NASA p.18-23.
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