J÷kulhlaup on Skei­arßrsandur from the GrÝmsv÷tn caldera

7th. of November 1996

Jokulhlaup started on the morning of November the 5th. quite abruptly. The growth was fast and many icebergs were floating in the flood water from the glacier reaching all the way to the sea. Grimsvotn tremour started at 21:30 on Monday 4th Nov, the jokulhlaup came out of the glacier 11 hrs later. Distance is about 50 km from Grimsvotn to the Skeidararsandur. The discharge growth was more sudden than was ever expected to be possible. While all was quiet at 0800 the flood had increase its discharge 80-100 times in less than 2 hours.

Following river outlets were flooded:

N˙psvotn flooding starts around 1720 on 5th of Nov.
Gigja, bridge fell at 13:00
Saeluhusakvisl lot of water flowed over the bridge
Skeidara strong current flow, bridge damaged

The estimated peak-flow was around 45.000 m3/s, that is about 10.000 to 15.000 m3/s higher than in the jokulhlaups of 1934 and 1938. Flood peak was reached at about 2300 hrs. The flood has been decreasing rapidly since 2300 hrs on 5th of Nov. The flood channel from Grimsvotn caldera can be clearly seen. It forms a depression like structure on the surface of the glacier dotted with several holes. It is estimated that the Grimsvotn lake has been totally emptied, since the glacier seal has been destroyed due to melting of the water. This has never occurred in Grimsvotn before. Such high melting can only be associated with lake water temperature greater or equal to 10 deg. celsius.

It is now clear that the total damage are about 10-15 milj. US$, these are the main constructions that were hit:

1) Skeidara bridge not destroyed but badly damaged.
2) Bridge over Gigja has disapered.
3) Saeluhusakvisl bridge standing but damaged. It was completely submerged during the flood.
4) Roads were damaged and at least 10 km totally washed away.
5) Electric lines and telephone cables damaged, partly washed away

A small eruption started in Bardarbunga around 1300 hrs on 6th of Nov. The eruption lasted for about 20 to 30 min. According to seismograms at the Meteological office, the eruption was initiated by some intrusive activity. The intrusive activity is based on recorded eruption tremor picked up by on of the seismometers. Eruption column reached about 4 km in to the air. Relation between pressure decrease due to the flooding have been suggested as the main cause of the eruption.