Q&A
Öræfajökull – frequent questions & answers
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Öræfajökull and Skeiðará river bridge in July 2014. The river has left its channel. Photo: Oddur Sigurðsson.
Question: Has Öræfajökull erupted in historical times?
Answer: Two eruptions are known, which occurred in 1362 CE and 1727 CE, both explosive. The eruption in 1362 is assessed to have a Volcanic Explosivity Index (VEI) equals to 6 and the following one in 1727 equals to 4. Annals mention other volcanic eruptions during the 14th century but they have not been confirmed. The eruptions caused major jökulhlaups, pyroclastic flows, heavy tephra fallout and ejection of ballistics. The glacial floods had a large geomorphic impact on the lowlands through flooding, formation of sandur plains (outwash deltas) and large quantities of ice blocks that took years or decades to melt. The pyroclastic flows and jökulhlaup caused by the 1362 eruption are thought to have resulted in the death of ~300 individuals. The magnitude of the 1362 jökulhlaup was of order 100,000 m3/s, whereas the 1727 flood was about half that size. In 1362 tephra fallout buried houses and villages with a deposit >40cm thick.
The Öræfajökull eruption in 1362 has been one of the largest eruption in Iceland and the second largest in Europe after the Vesuvius 79 AD.
Question: What are the possible hazards related to an eruption in Öræfajökull?
Answer: Tephrafallout, ash cloud, lightning, pyroclastic flows, jökulhlaup /glacial outburst floods, ballistics, lava flows, gas pollution. They will occur over different time frames, with probably the flood to be the first sub-aerial evidence of a sub-glacial eruption started. Given the time for the magma to break through the ice, the ash column will start to raise and tephra fallout will take place. Ballistics might be ejected several kms away from the main vent. The generated ash cloud will be transported down-wind by the prevailing winds and lightings might take place in the very vicinity of the vent and in the cloud far away the volcano.
Question: Should an eruption occur, where from the glacier can the jökulhlaup be expected?
Answer: It depends on the location and type of the eruption. Three types of glacial outbursts can be thought about:
- Floods resulting from an eruption in the caldera, where the ice is up to 500 m thick. Large eruptions can melt of order 100,000 m3/s. Jökulhlaups can be expected from Virkisjökull-Falljökull, Kotárjökull and Kvíárjökull.
- Floods resulting from fissure eruptions on the upper flanks where the ice is 50–100 m thick. Expected melting in eruptions is in the range 1,000–10,000 m3/s. Jökulhlaups of this type can happen anywhere on the slopes from Virkisjökull in the west to Hrútárjökull in the east.
- Floods resulting from hot (300–600°C) pyroclastic density currents in large explosive eruptions (as occurred in 1362 CE). The discharge may be in the range 1,000–20,000 m3/s. Such jökulhlaups can occur anywhere on the slopes from Svínafellsjökull in the west to Hrútárjökull in the east.
- Geothermal meltwater may get trapped below depressions in the glacier surface and escape from there in jökulhlaups.
- The first two types of floods happen at the very onset of an eruption.
Question: How much of the lowland surrounding the volcano is exposed to jökulhlaups?
Answer: The major part of the lowland between the rivers Skaftafellsá and Breiðá (340 km2) is susceptible to flooding because of jökulhlaups descending the western and southern slopes of Öræfajökull. Very few settlements can be considered as safe.
Question: What damage can jökulhlaup cause?
Answer: Jökulhlaups from Öræfajökull can cause complete destruction of man-made structures almost anywhere in sectors at risk of flooding. The potential impact of major floods on the local economy is high.
Question: How much time is available at the onset of an eruption for a full evacuation of the floodplain?
Answer: Jökulhlaups can be very swift, reaching the lowlands in as little as 20–30 minutes from the onset of an eruption.
Question: Should an eruption occur, will be the aviation affected?
Answer: Given the known explosive style of Öræfajökull volcano, we might expect an explosive eruption in the future as well. In that case volcanic particles will be injected in the atmosphere and an ash cloud will be generated. It will be possible to forecast, with some uncertainties, toward which direction the cloud will move. The aviation sector will respond to this situation by following its contingency plans and assessing from time to time if flights will be allowed or not to fly in those areas forecasted to be contaminated by volcanic ash. The effect on the aviation sector also depends on how prolonged will be the eruption and for how long the emission of ash will continue. However, it is often very hard to assess the temporal evolution of an eruption once it has started.
Question: Should an eruption occur, will be the main city of Reykjavik affected by tephra fallout?
Answer: Recent numerical studies show that given an eruption of the same size as in 1362, Reykjavik has a likelihood between 5 and 25% to be covered by 1 mm of ash. This likelihood is less than 5% for a deposit 1-cm thick.
