Eldfell
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Eldfell | |
---|---|
Highest point | |
Elevation | 200 m (660 ft) |
Prominence | 200 m (660 ft) |
Coordinates | 63°25′57″N 20°14′51″W / 63.43250°N 20.24750°W |
Geography | |
Location | Heimaey island, Vestmannaeyjar, Iceland |
Geology | |
Age of rock | Historical |
Mountain type | Volcanic cone |
Volcanic arc/belt | Southern Volcanic Flank Zone[1] |
Last eruption | January to June 1973 |
Eldfell is a
The eruption caused a major crisis for the island and led to its temporary
After the eruption, the islanders used heat from the cooling lava flows to provide hot water and to generate electricity. They also used some of the extensive tephra, fall-out of airborne volcanic material, to extend the runway at the island's small airport and as landfill on which 200 new houses were built.[2]
Background
Iceland is a region of frequent volcanic activity, due to its location astride the Mid-Atlantic Ridge, where the North American and Eurasian Plates are moving apart, and also over the Iceland hotspot, which greatly enhances the volcanic activity. It is estimated that a third of all the basaltic lava erupted in the world in recorded history has been produced by Icelandic eruptions.[citation needed]
The
The Vestmannaeyjar archipelago was settled in about 874 AD, originally by escaped Insular slaves belonging to
The eruption begins
At about 20:00 on 21 January 1973, a series of small tremors began to occur around Heimaey. They were too weak to be felt by the residents of the island, but a seismic station 60 kilometres (37 mi) away, near the mainland, recorded over 100 large tremors between 01:00 and 03:00 on 22 January that appeared to be emanating from south of Heimaey. The tremors continued at a reduced rate until 11:00 that day, after which they stopped until 23:00 that evening. From 23:00 until 01:34 on 23 January, seven tremors were detected that grew shallower and more intense, while the epicenter moved closer to the town of Vestmannaeyjar.[3] The largest tremor measured 2.7 on the
Small tremors are very common at plate boundaries, and nothing here indicated that they heralded a major eruption.[citation needed] The onset of the eruption was therefore almost entirely unexpected. At about 01:55 on 23 January, a fissure opened up on the eastern side of the island, barely a kilometre away from the centre of the town of Heimaey, approximately 200 metres (650 ft) east of Kirkjubær (Church farm), where the island's church had once been located.[citation needed]
The fissure rapidly extended from 300 metres to a length of 2 kilometres (1.2 mi), crossing the island from one shore to the other. Submarine activity also occurred just offshore at the northern and southern ends of the fissure. Spectacular
During the early days of the eruption, the rate of lava and
The first lavas erupted by Eldfell had a mugearitic chemical composition but within a few weeks the volcano was erupting less fractionated lavas which had a hawaiitic composition.[5]
By early May, the lava flow was between 9.1 and 21.0 m (10 and 23 yd) in height. It averaged more than 37 m (40 yd) and in some places was as much as 100 m (110 yd) thick. The flow carried off large blocks from the main cone that had broken off, as well as volcanic bombs. "The viscosity of the lava fragments ejected by the blasts was, for basalt, relatively high. Very little spatter was produced and scoria bombs sometimes broke up explosively in flight (presumably due to rapid vesiculation), and by rapid impact on landing."[4] The high viscosity led to a "massive, blocky ʻaʻā lava flow which moved slowly but relentlessly toward the north, northeast, and east."[6]
Volcanic gases were collected from several locations. Gases collected at sea along the submerged part of active eruptive fissure were dominantly carbon dioxide and gases from cooling submerged lava flows were about 70 percent hydrogen. (Richard & James, 1983) Poisonous gas was found at low areas on the eastern part of Vestmannaeyjar. A wall was constructed between the vent and town to divert the gas, and a long trench was excavated for the steam to escape. However, none of these measures were completely effective. (Richard & James, 1983)
Evacuation
In the early hours of the eruption, the Icelandic State Civil Defence Organisation evacuated the entire population of Heimaey, having previously developed evacuation plans for an emergency such as this. The evacuation was necessary because
Because of severe storms in the days before the eruption, almost the entire fishing fleet was in the harbour, a stroke of luck which greatly assisted the organisation of the rapid evacuation. The population was alerted to the situation by fire engines sounding their sirens, and gathered by the harbour with just the small amount of possessions they were able to carry. The first boats left for Þorlákshöfn at about 02:30, just half an hour after the start of the eruption.[citation needed]
Most of the population left the island by boat. Fortunately, the lava flows and
Destruction of houses, creation of land
Houses close to the rift were soon destroyed by lava flows and tephra fall.
By early February, the heavy tephra fall had abated, but lava flows began to cause serious damage. Submarine activity just north of the fissure severed an electric power cable and a water pipeline which supplied electrical power and water from the Icelandic mainland, and lava began to flow towards the
Lava flows also moved into the sea east of the island, creating new land that would eventually add over two square kilometres (3⁄4 sq mi) to the island, and into the eastern parts of town, destroying several hundred houses. The flows were thick and blocky ʻaʻā lava (Icelandic: apalhraun) flows, and covered the ground to average depths of about 40 metre (130 ft), reaching 100 metre (330 ft) thick in places. Later on in the eruption, a surge of lava destroyed one fish processing plant and damaged two others, and also demolished the town's power generating plant.[citation needed]
Despite the eruption's close proximity to the town and the extensive property damage, only one fatality could be attributed to the eruption - a man who had broken into a chemist's store to acquire drugs was suffocated by toxic fumes.[citation needed] Carbon dioxide, with small amounts of poisonous gases, became concentrated in many buildings partially buried by tephra, and several other people were affected when entering these buildings.[citation needed]
Efforts to mitigate the hazards presented by the accumulation of poisonous gas included the building of a large tephra wall to divert gases away from the town, and the digging of a trench to channel away the CO2 (carbon dioxide). These defences were only partially effective, as they relied on the assumption that the gases were produced at the vent, and flowed into the town from there. It is believed that as least some of the CO2 originated deep within the volcanic conduit and percolated through older volcanic rocks, rising directly into the town.[citation needed]
Lava-cooling operations
The possibility of lava flows cutting off the harbour was the most significant threat facing the town. One contingency plan devised, should the harbour be closed off, was to cut through a low sand spit on the north side of the island to provide a new channel into the harbour, but it was hoped that if the lava flow could be slowed, this would not be necessary. Lava flows had been sprayed with water in attempts to slow them in Hawaii and on Mount Etna, but these had been rather small-scale operations with limited success. However, Professor Þorbjörn Sigurgeirsson carried out an experiment that proved that further advances of the lava could be impeded by prematurely solidifying the advancing lava-flow front.[9]
The first attempt to slow the lava flow by spraying the leading edge with sea water began on 6 February, and although the volume of water being pumped on was rather small at 100
The pumping capacity was increased in early March, when a large chunk of the crater wall broke away from the summit of Eldfell and began to be carried along the top of the lava flow towards the harbour. The chunk, dubbed Flakkarinn (The Wanderer), would have seriously threatened the viability of the harbour if it had reached it, and the dredging boat Sandey was brought in on 1 March to prevent its advance. Professor Þorbjörn Sigurgeirsson provided advice to the pumping crews on where to direct their efforts to most efficiently slow the flows. Eventually the Wanderer broke up into two pieces which both stopped approximately 100 metres (330 ft) from the harbour mouth.[citation needed]
The ensuing lava-cooling operations were the most ambitious that had ever been undertaken. Sandey was able to spray up to 400 litres per second (105 US gallons per second) onto the advancing flow, and a network of pipes was laid on top of the lava to distribute the seawater over as wide an area as possible. Wooden supports for the pipes caught fire where the lava was hottest, and even aluminium supports melted, but the pipes themselves were prevented from melting by the cold seawater flowing through them. Up to 12,000 square metres (3 acres) of lava flow could be cooled at one time, with internal barriers then being created within the flow, which thickened and piled up upon itself.[citation needed]
The work involved in laying pipes over an active lava flow was highly dangerous, with low visibility due to the extensive emission of steam. Rough tracks were made onto the flow by bulldozing tephra, but these tracks quickly became very uneven and moved several metres a day.[citation needed] The pipelayers used bulldozers and walkie-talkies to advance through the steam to lay more pipes.[citation needed] The workers dubbed themselves 'The Suicide Squad', and managed to lay pipes up to 130 metres (430 ft) inward from the flow front, directly over the advance. Although several men sustained minor burns, no serious injuries were received.[citation needed]
By the end of March, a fifth of the town had been covered by lava flows, and increased pumping capacity was required. Thirty-two pumps, each with a capacity of up to 1000 litres per second (265 US gallons per second), were brought in from the United States. After these pumps began to cool the flow advancing towards the town, its movement slowed dramatically and soon stopped. Failure of pump shafts became a problem after a few weeks, probably because they were designed for pumping oil rather than water, and new and improved shafts had to be manufactured in Reykjavík and brought in.[citation needed]
One notable feature of the lava cooling operation was the deposit of large amounts of salt where seawater was sprayed onto the lava. Large expanses of flow became encrusted with extensive white deposits, and it was estimated that up to 220,000 tonnes (240,000 short tons) of salt was deposited in total.[citation needed]
Sigurgeirsson called these protective measures "undoubtedly the most extensive that have ever been used in a volcanic eruption" and said that "had it not been for the cooling, the lava tongue [into the harbor] could be expected to…extend further along its direction of movement…for a whole month longer than it actually did. It failed by only about 100 meters to block the entrance to the harbor".[10]
The cooling operation ended on 10 July 1973, and approximately 7.3 million cubic metres of seawater were pumped. This eruption was a special case where the method used to control the lava was suited to local conditions. Firstly, the initial eruption was only 1,000 m (1,100 yd) from the centre of town and harbour. Next, the flow of lava was slow and allowing time to plan and carry out control. Thirdly, sea water was available in its nearby harbour and lastly, it was easy to move pipes and pump equipment as the transport system by sea and road was good. (Richard & James, 1983) The entire operation cost a total of
The eruption made headlines around the world when it began, and was covered constantly by Icelandic news crews throughout. In Europe, the eruption was one of the biggest news items while it continued, competing for front-page space with breakthroughs then being made in the
Final stages
The volume of lava being emitted during the eruption fell steadily after the first few days. From its initial rate of 100 cubic metres per second (3,500 cu ft/s), the emission rate fell to about 60 m3/s (2,100 cu ft/s) by 8 February, and just 10 m3/s (350 cu ft/s) by the middle of March. The decline was slower after that, but by the middle of April the flow rate had fallen to about 5 m3/s (180 cu ft/s).[citation needed]
Short-lived submarine activity was discovered by a fishing vessel on 26 May, about four kilometres (two nautical miles) northeast of Heimaey and 1 km (1⁄2 nmi) off the coast of the mainland. The eruption finally came to an end in early July, when flowing lava was no longer visible, although subsurface flows may have continued for a few days longer. Shortly before the end of the eruption, a tiltmeter 1,150 m (3,770 ft) from the crater which had been measuring ground deformation throughout the eruption detected subsidence towards the crater, implying that the shallow magma chamber which had fed the eruption was emptying out.[citation needed]
In total, the volume of lava and tephra emitted during the five-month eruption was estimated to be about 0.25 km3 (330,000,000 cu yd). About 2.5 km2 (1 sq mi) of new land was added to the island, increasing its pre-eruption area by some 20%. In the end, the harbour entrance was narrowed considerably but not closed off, and the new lava flow acted as a breakwater, improving the shelter afforded by the harbour. Flakkarinn rafted several hundred metres towards the harbour along the top of the lava flow, but came to a halt well away from the water's edge.[citation needed]
Heimaey since the eruption
By the end of 1975, the population of the Westman Islands had returned to roughly 85% of its pre-eruption level.[14] 42% among those with destroyed houses did not return before the end of 1975, while the rate was only 27% among those whose houses were not destroyed.[14] By 1974, fishing companies in the Westman Islands were back to normal production levels.[14] Counter-intuitively, the new lava field actually improved the harbour in Westman Islands.[14] Also counter-intuitive, the forced displacement had a large positive causal effect on both the earnings and education for those who were younger than 25 years old at the time of the eruption.[14]
The insides of lava flows can remain at temperatures of several hundred degrees for many years due to the very low
The tephra produced by the eruption was used to extend the runways at the island's small airport, and also as
By the end of the eruption, Eldfell stood about 220 metres (720 ft) above sea level. Since then, its height has dropped by 18 to 20 metres (60 to 65 feet), due to slumping and compacting of the unconsolidated
See also
References
- ^ Trønnes, Reidar G. "Geology and geodynamics of Iceland" (PDF). Nordic Volcanological Institute, University of Iceland. Archived from the original (PDF) on 14 August 2010. Retrieved 14 May 2009.
- ^ Reed, Mark. "How to Survive the next Icelandic Strato Volcanic Ash Cloud". Archived from the original on 10 June 2015.
- ^ S2CID 4163208.
- ^ S2CID 129008893.
- .
- ^ USGS. Retrieved 15 November 2008.
- ^ Kölbl, Richard. "Heimaey island, Vestmannaeyjar, Iceland".
- ^ "OECD Economic Surveys" (PDF). October 2015. p. 24.
- ^ Lava-Cooling Operations During the 1973 Eruption of Eldfell Volcano, Heimaey, Vestmannaeyjar, Iceland U.S. Geological Survey Open-File Report 97-724
- USGS. Retrieved 15 November 2008.
- USGS. Retrieved 15 November 2008.
- National Geographic Magazine. 144 (1): 40–67.
- ^ "Welcome to Vestmannaeyjar" (PDF). Vestmannaeyjar, Iceland. Archived from the original (PDF) on 19 December 2008. Retrieved 15 November 2008.
- ^ doi:10.3386/w22392.
Further reading
- Bertmarks förlag, K.G., Aktuellt 1973 (1973) ISSN 0343-6993, pp. 97–104
- Kristjansson L., Simon I., Cohen M.L., Björnsson S. (1975), Ground tilt measurements during the 1973 Heimaey eruption, Journal of Geophysical Research, v. 80, pp. 2951–2954
- Mattsson H., Hoskuldsson A. (2003), Geology of the Heimaey volcanic centre, south Iceland: early evolution of a central volcano in a propagating rift?, Journal of Volcanology and Geothermal Research, v. 127, pp. 55–71
- ISBN 0-374-12890-1. The middle third of this book is devoted to this eruption, its immediate effects, the lava-cooling operations, and the people involved and affected.
External links
- VolcanoWorld information
- Eruption description from www.VisitWestmanIslands.com
- A description of the eruption
- A description of the eruption and evacuation
- "Vestmannaeyjar". Global Volcanism Program. Smithsonian Institution.
- Pompei of the north. The plan is to excavate 7–10 houses that were covered by ash.