On September 30th 1996, a subglacial eruption started between the Grimsvotn caldera and Bardarbunga (2000m). It melted a 3,5 km (2 miles) long and 500 m wide area of the 600 m thick ice shield, which was named Gjalp. The meltwater, 300-400 m³/sec., filled the caldera during the entire eruption period to the extent of about 3,2 km³ until the glacier burst started in the beginning of November. The eruption was declared finished on November 14th. The flood kept increasing until it peaked on November 5th at 22;30. One bridge was swept away completely and the country’s longest bridge was cut at both ends. Prior to this glacier burst, River Skeidara was flooded in April, so the water volume of the caldera was minimal. The first damages to property soon after the beginning of the November flood were the telephone and glass fiber connections across the aluvial plains, which led to re-routing via the northern part of the country. The first illustrated news from the glacier burst appeared in the afternoon of the first day (5/11). Warnings were issued to the captains of the fishing fleet off the south coast not to venture to close to the spillage area because of the strong currents of the flood wave entering the sea and all the mud and gravel carried with it. Two days later the caldera was empty again and the destruction was evaluated. It took about three weeks to build a provisional bridge and repair the longest bridge. The ring road was opened again. On November 7th, scientists estimated, that the enormous blocks of ice, which had been carried long distances from the edge of the glacier and spread all over the flooded area, would take at least two years to melt. They, however, were proved wrong, because the melting was extremely fast, only a few months.
A small eruption, just south of the southernmost crater of the previous eruption (Gjalp), took place on November 6th and created a depression in the ice cap. The next day another long depression was created, when the flood water tunnel under the ice collapsed from the exit of the caldera and far to the south. The increased geothermal activity in the wake of the eruptions continued for years and increased the flow of water into the caldera, which was not filled up again to cause the regular glacier bursts like before. Water collection in the caldera did not commence until the drainage pass had been filled with massive ice. The enormous fissure created by the 1996 eruption was soon filled with ice and snow and left behind a dangerously crevassed depression in the ice landscape. The construction of the new concrete bridge was finished in 1998
In 1998 (December 18th) another subglacial eruption started in the southernmost part of the caldera. It was first spotted from a plane at 09;32, only 11 minutes after the beginning. The plume of the eruption reached the altitude of 10 kilometres (6 miles) and most of the ash fell on the ice cap 3-4 miles southeast of the crater. The following day the eruption started dwindling and the wind carried the ash to the north. Ten days later, the eruption was declared finished.
In 2004 (November 1st, 21;50) a subglacial eruption started under the ice shield of the southwestern part of the caldera and lasted 4-5 days. The plume reached 13 km altitude. The eruption soon melted the ice above and continued in the open until it came to an end during the night of day five. It co-incided with a normal glacier burst of River Skeidara and added to its volume, which also affected the discharge of rivers Gigja and Nupsvotn further west on the outwash plain. The peak of the flooding reached 4,900 m³/sec.
In 2010 (October 31st ) a glacier burst of river Gigjukvisl started. Sicentists expected it to follow similiar lines as in 2004, but were surprised by the quicker increase in volume the next day (>600 m³/sec.). They do not exclude the possibility of a subglacial eruption with the decreasing pressure in the emtying caldera 50 kilometres north of the southern edge, where the flood water appears.
On November 3rd, at ten o’clock a.m., the flood water volume at the bridge was measured 2600 m³/sec, and a peak of 4.000 m³/sec was expected in the afternoon. At 02:30 a.m. increased earthquake activity was observed in the Grimsvotn caldera. It was probably caused by subglacial water flow changes.
The glacier burst peaked at 3.500 m³/sec, somewhat less than expected, and the water continued receding until the end was declared on November 9th without any volcanic activity.
May 21st 2011 an ash plume was reported at 19:15, seen from Mt Lomagnupur on the south coast and village Hella in the southwestern lowlands. At the meteorological centre in Reykjavik, where volcanoes are monitored constantly, the scientists observed tremours and earthquakes at 17:30, which pointed to a pending eruption and alerted the media. They immediately prepared a flight to the area for further information. The eruption started just before 19:00 o’clock.
The ash was carried by northwesterly winds to the Glacial Lagoon on the southeast coast, where it started falling at 22:00. At 22:07 the plume reached 15 kilometres elevation. At 22:45 the Glacial Lagoon area was totally darkened, no visibility.
The eruption has been placed in the ice free southwestern part of the Grimsvotn area and the ashes are also falling on the Skeidararsandur outwash plain and is very light in colour. Road #1 through that area was closed because of lack of visibility a few minutes ago.
At 23:16, the plume had reach the hight of 20 kilometres, and scientists could not predict how the eruption would develope. They said, however, that it was much more powerful than in 2004. This statement was issued after the first reconnaissance flight to the volcano this evening, and also, that a minor glacier burst was probably pending approximately 12 hours after the beginning of the eruption, if there were sufficient water in the Grimsvotn caldera.
Fine ashes have already fallen as far east as in fishing village Hofn and as far west as village Kirkjubaejarklaustur.
May 22nd. International flights were postphoned from Keflavik airport at 08:00 for the time being and all domistic flights as well. This morning fine ashes fell in river Tjorsa area in the southwestern lowlands. The ash cloud was about 3 kilometres high and planes could fly above it further east. Scientists have declared this eruption of Grimsvotn its greatest for over a century.
The ring road between Kirkjubaejarklaustur and Freysnes is closed because of no or very poor visibility.
A renowned geophysicist claims today, after observing the eruption from the air, that the eruption is gradually subsiding, but could last for a few days. Many Icelanders fear, that the Metoffice (London VAAC) in England is going to react equally hysterically as last year and ban flights all over Europe on usubstantiated grounds or evidence.
The ash plume went down to ten kilometres in the afternoon and stayed between ten and fifteen in the evening. Very few of the domestic animals, sheep, horses and cattle, have suffered. A few sheep were found dead in home fields, where they are grazing during the lambing season.
The ashes are brown in colour, not gray as during last year’s eruption of Eyjafjallajokull, and most likely contain less fluor.
The ash cloud reached the capital area of Iceland in the evening.
May 24th. Today the eruption has been stable and gradually subsiding. Eruption tremours, monitored by the Icelandic Metoffice, remain constant and the plume has been 8 kilometres high the whole day. The main ash fall sector lies between village Vik in the middle of the south coast and farm Kvisker, south east of glacier Oraefajokull, the country’s highest mountain. Stormy weather has added to the discomfort of the people in the south east and made it difficult to stay outdoors. Schools were cancelled yesterday and today and road #1 between Vik and Freysnes has been closed.
According to forecast, ash clouds are expected to reach the northern part of Russia and Ireland and Scotland tomorrow morning.
May 24th. The ash plume reaches three to five kilometres elevation today. The progress of the eruption is as predicted to the extent, that it subsides gradually. The tephra emission of the eruptive fissure is estimatated 100 m3/sec compared to 2000-3000 m3/sec yesterday. Ash has fallen in most parts of the country without affecting domestic flights, which were only cancelled during the second day of the eruption. International flights were cancelled to and from England, Denmark and Norway. More people seem to disagree with the conclusions of London VAAC, and use their own judgement. Ryan Air cancelled flights to and between Ireland and Scotland after declaring unchanged flight schedules today. The Norwegians decided to ignore the VAAC warnings and continued their scheduled flights.
The Icelandic authorities opened the ring road at 19:00 o’clock. A team of scientists prepared a research expedition to the eruption area. It headed for the glacier snout Skalafellsjokull, where it continued in its special vehicles on the ice to the Grimsvotn area. In the evening the eruption continued dwindling, at 20:00, only 50 m3/sec, and it was highly likely, that the ash production would come to an end soon. During the 3-4 days of the eruption, much greater volume of ash was emitted than during the whole Eyjafjalla-eruption (April 14th-May 23rd) last year.
All main airports of the country were closed at 23:00 to 08:00 next morning, when the decision was to be revised.
May 25th. Keflavik international airport was opened at 8 o’clock this morning. According to people present in the eruption area this morning, there is no eruptive activity. The crater mostly emits steam during frequent, but small ash explosions, at least for the time being. Ash only falls in its immediate neighbourhood. The eruption might be over or pausing. Some German airports were closed to noon. Authorities do not expect any further flight interruptions because of this eruption.
May 26th. The intermittent and differently powerful explosions of the eruptive fissure continued. A twenty minutes long series of explosions sent the ash plume eight kilometres in the air and then lesser activity prevailed. The eruption is therefore not quite over.
May 28th. A coast guard plane reported a 1,5 kilometre high plume of steam. Scientist say, that ash plumes can still be expected.
May 30th. The eruption is officially over.
A small eruption
Sources: The Icelandic media and scientists.