Grimsvotn eruption diaries,

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GRIMSVOTN
ERUPTIONS' DIARIES

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September 30, 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 /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
/sec.


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