The following was received by the Smithsonian's Global Volcanism Network. This report is preliminary and subject to change as the event is studied in more detail. We will forward additional significant information as it becomes available.
A subglacial eruption near the Bardarbunga and Grimsvotn volcanoes in Iceland.
An eruption broke out beneath the Vatnajokull glacier in Central Iceland in the evening of September 30. The eruption was preceded by an unusual sequence of earthquakes, beginning on September 29 with a magnitude 5 event in the Bardarbunga caldera. Similar earthquakes have occurred in Bardarbunga many times during the last 22 years, without eruptive activity and almost without aftershocks. This time the earthquake was followed by an intense swarm of small earthquakes, that spread out to the neighboring volcanoes Grimsvotn and Hamarinn. A warning of a possible eruption was issued to air traffic on September 30 at 19 h. Later that evening the earthquake activity near Grimsvotn decreased markedly, while that of Bardarbunga continued. At about 22 h the seismograph at Grimsvotn began recording continuous eruption tremor with small amplitude. The amplitude increased very slowly during the next hours and reached a maximum at about 6 h in the morning of October 1. A large depression in the glacier ice of Vatnajokull was discovered from overflying aeroplanes in the early hours.
The glacier is apparently being melted by an eruption on a 4 km long fissure beneath the glacier, which is 400-600 m thick in this location. The fissure has a NNE-SSW strike and is located on the northern flank of the Grimsvotn central volcano. The melt water is draining into the Grimsvotn caldera and raising the ice shelf on the caldera lake. The eruption continues at the time of writing (14 h UTC, October 1).
The present eruption is a continuation of a remarkable series of seismic and magmatic events in the Vatnajokull area that began in 1995: July 1995: A glacier flood from a subglacial geothermal area on Loki Ridge (Eastern Cauldron) NW of Grimsvotn. The draining of the water reservoir was followed by a distinct tremor episode, presumably a small eruption triggered by the pressure release. This event was followed by a general increase in seismicity during the next few months.
February 1996: An intense earthquake swarm centered on the Hamarinn Volcano, lasted a week.
August 1996: A glacier flood from a subglacial geothermal area on Loki Ridge (Western Cauldron) NW of Grimsvotn. The draining of the water reservoir was followed by a tremor episode, presumably a small eruption triggered by the pressure release. This event was followed by increased seismicity during the next few weeks.
September 1996: Present activity: Large earthquake, intense earthquake swarm and an eruption N of Grimsvotn.
Pall Einarsson Science Institute, University of Iceland
The following was received by the Smithsonian's Global Volcanism Network. This report is preliminary and subject to change as the event is studied in more detail. We will forward additional significant information as it becomes available.
Wednesday, 2nd October 1996 09:30
Last Sunday, 30th Sept there started a series of earthquakes in Brdarbunga, in Vatnajokull. This event continued on Monday, and at 22:30 it was evident that a volcanic eruption had started below the glacier. The eruption site is east of Bardarbunga.
In Thuesday 1. Okt, observation indicated that a 5-6 km long row of cauldrons was growing through the day, being roughly 100 m deep, and 2 km wide. The eruption site is between Bardarbunga and Grimsvotn, and is a fissure eruption. The glacier is 600 m thick over the eruption site and the cauldrons indicate a flow of water to the Grimsvotn caldera to SE. In the Grimswotn caldera is a lake that periodically surges to south, under Skaftarjokull forming "jokulhlaup". It was estimated that the eruption had filled 25% of the volume of the caldera and a surge is evident if the eruption continues. Weather was fine throughout the day.
Today 2nd Okt is SE rain and storm, visiblitiy low and observation from air difficult. From seismometers it is evident that the eruption continues and in 09 news it was reported that the eruption had broken through the glacier and the eruption column is in the order of 5 km. It is not possible to forcast the length of the eruption, several small eruptions have occurred in this area but also some of the largest in Iceland are from this fissure system.
Wednesday, 2nd October 1996, 10:00
Eruption below Vatnajokull glacier is more concentrated in one place as is usual in such eruptions.
Flight observation before 09 this morning confirmed the ash-column to reach several km. This eruption is at the same site as in 1938. The thickness of the glacier is thinner at this place as the 1938 eruption did build a subglacial ridge. The glacier is around 450 m thick where the eruption did erupt through the glacier. The 1938 eruption is expected to have lasted about 1 week, perhaps longer as it was only observed when it had melted throug the glacier.
Water continues to flow to Grimsvotn caldera at a rate about 5000 m3/sek. A surge in Skeidara river is expected to begin tomorrow, after evt. 24 hrs if this inflow rate continues.
Ash is travelling N and NE at the speed of 70 km/h and in the next few hours it is supposed to fall in N and E Iceland. All flight is cancelled in N and E Iceland at the moment.
Wednesday, 2nd October 1996, 12:00
Eruption column is 15000 feet, and now the eruption fissure is 10 km long and has extended through the glacier at 2 sites, the second site is 10 km to the north of the opening that opened at 05 this morning. Ash has started to fall in N Iceland Hazardzone is now Vatnajokull, Axarfjordur to Hunafloi in N Iceland and as a low pressure is going over Iceland, ash can fall anywhere the next 24 hours.
Helgi Torfason [email protected]
The following was received by the Smithsonian's Global Volcanism Network. This report is preliminary and subject to change as the event is studied in more detail. We will forward additional significant information as it becomes available.
The eruption is still going strong. Ash-fall has not been a problem, mainly it has been falling around the vent. The eruption seems to have concentrated in one vent before the weekend, as is common in fissure eruptions. The site of the volcanic fissure is according to the Weather bureau at N 64 30-32' W 17 22'. The eruption column has been observed this morning. Earthquakes have been less than last week, the activity is now mainly magma flowing up through fractures in the crust.
The jokulhlaup/surge in Skeidararjokull has not started, the water level is 20-25 m higher than last summer when the surge was 3000 m3/sec in the peak. It is still estimated that the coming jokulhlaup will be in the order of 10-15,000 m3/sec. The experts in these surges are astonished that the water has not yet started to flow under the glacier and have stopped forecasting when it will start, - nature is, as so often before, rather behind in solving complicated hydrologic equations!
Bad weather is now in Iceland, roof blowing of houses in N Iceland and roof-plates being lifting off here and there. The worst weather is now in N Iceland. Strong wind is in S Iceland but not a lot of rain. It is expected that weather will be rather on the bad side this week, but as meteorologists are better telling us how the weather is than how it will be, we remain optimistic.
A lot of photographs have been taken of the eruption, the best ones probably by the press. Those who want to buy photos could try the newspaper Morgunbladid, (phone: +354-569-1100, fax: +354-569-1181).
The best video-recordings are by Omar Ragnarsson Sjonvarpid/ The Icelandic
national TV-station
(fax: +354-515-3808, phone: +354-515-3900). No doubt some royalties will be charged, but as this is not my expertise,
you better contact them.
Information, images, updates etc from the The Nordic Volcanological Institute is now at: http://www.norvol.hi.is/
Please note that because of the unexpected heavy load being placed on the NVI server, Michigan Technological University has agreed to mirror eruption information from their site at: http://www.geo.mtu.edu/volcanoes/iceland/vatnajokull/. North American users are especially encouraged to use the mirror site. As it has now a proper page on the eruption, images and so on I do not think it is necessary that I continue these messages.
Best regards and thanks for encouraging responds
Helgi Torfason
National Energy Authority
Grensasvegur 9
108 Reykjavik