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Articles

Grímsvötn 2010

jökulhlaup - glacier outburst flood in 2010

3.11.2010

Jökulhlaup from Grímsvötn subsides - 5 November 2010

The jökulhlaup (glacial outburst flood) from Grímsvötn that began near the end of October is now coming to an end. See thorough description in news on front page.

Assessment - 5 November 2010

Tremor levels at seismic station 'grf' have reduced slightly in the last 24 hours. Discharge measurements in the Gígja river show that the jökulhlaup is waning rapidly. Presently, there are no detectable signs of the beginning of a volcanic eruption at Grimsvötn.

Information in status report nr. 5 issued collectively by the Icelandic Meteorological Office and the Institute of the Earth Sciences, University of Iceland, 5 November 2010 at 17:00.

This is the last status report for the Grímsvötn jökulhlaup. If signs of volcanic activity occur, we will resume these reports immediately.

Assessment

Tremor levels at the seismic station on Grímsfjall (grf) have declined considerably. Discharge measurements from the Gígja bridge showed that the jökulhlaup peaked on Wedenesday 3nd November between 13:00 and 14:00 GMT; at this time, the maximum discharge was ~2,600 m3/s. Electrical conductively levels in Gígja river remain high, signifying continued drainage of meltwater from Grímsvötn. Presently, there are no detectable signs of the beginning of a volcanic eruption at Grimsvötn.

Further information in status report nr. 4 issued collectively by the Icelandic Meteorological Office and the Institute of the Earth Sciences, University of Iceland, 4 November 2010 at 17:00.

Aerial view

The following photographs were taken 3rd November during scientific flight with the Icelandic Coast Guard (TF-SIF): Matthew J. Roberts and Egill Axelsson, Icelandic Meteorological Office.

Skeiðarárjökull
jökulhlaup
Aerial view of debris-laden floodwater flowing along the terminus of Skeiðarárjökull near to the centre-line of the glacier; photograph taken at 13:06 GMT on 03 Nov. 2010.
Skeiðarárjökull
jökulhlaup
Aerial view of floodwater draining along the edge of Skeiðarárjökull at 13:07 GMT on 03 Nov. 2010. Water is flowing from right to left around a sedimentary feature from the November 1996 jökulhlaup; this feature was originally an ice-walled canyon, which formed during the rising stage of the 1996 jökulhlaup.
Skeiðarárjökull
jökulhlaup
Floodwater burst from Skeiðarárjökull via several vents on the eastern side of the terminus. Recent retreat of the glacier has created a series of trenches and basins parallel to the ice margin. This photograph shows floodwater draining through the westernmost lake near to the ice margin; the head of the Gígjukvísl channel can be seen in the upper left of the image. Photograph taken at 13:07 GMT on 03 Nov. 2010.
Gígjukvísl bridge
jökulhlaup
Aerial view of the Gígjukvísl bridge near the height of the jökulhlaup at 13:09 GMT on 03 Nov. 2010. Note the damaged electrical pylon in the centre of the channel, immediately downstream from the bridge.
Gígjukvísl bridge
jökulhlaup
Aerial view of the Gígjukvísl bridge from the north-east at 13:13 GMT on 03 Nov. 2010. Flow direction is from the lower right to the upper left. Note how floodwater accumulates upstream from the bridge due to the constriction created by the levees of the bridge.
At Grímsfjall mountain in Vatnajökull
jökulhlaup
Aerial view of the eastern edge of Grímsfjall at 13:25 GMT on 03 Nov. 2010. Fresh crevasses at the base of Grímsfjall illustrate how the ice-cover over the subglacial lake has subsided during the jökulhlaup. The elongated trench in the ice gives an indication of the lake surface. Water presumably drained from this region around the eastern edge of Grímsfjall on a ~50 km pathway beneath Skeiðarárjökull.

Assessment - 3 November 2010

Seismic tremor at Grímsvötn has continued to amplify, indicating enhanced drainage of water from the subglacial lake. Aerial observations over Grímsvötn revealed no signs of volcanic activity.

Discharge continued to increase in the Gígjukvísl river, although it is likely that the jökulhlaup is at, or nearing, maximum discharge. Presently, there are no detectable signs of the beginning of a volcanic eruption at Grímsvötn.

Further information in status report nr. 3 issued collectively by the Icelandic Meteorological Office and the Institute of the Earth Sciences, University of Iceland, 3 November 2010 at 17:00.

Status reports

The Icelandic Meteorological Office and The Institute of the Earth Sciences, University of Iceland, issue collective status reports:

2 November 2010 at 16:00 Status report nr. 2

1 November 2010 at 17:00 Status report nr. 1

Glacier outburst flood - reported 1 November 2010

On October 31, a glacier outburst flood (jökulhlaup*) emerged from beneath the Skeiðarárjökull glacier, a southern outlet of the Vatnajökull ice cap. The floodwaters originate in the subglacial lake Grímsvötn, 50 km upstream from the glacier margin. The lake has been a source of such floods for centuries, but the size of the floods has varied greatly. The present flood is small and no threat to roads and bridges is imminent.

The graph below shows data from a hydrometric station in the river Gígjukvísl Oct. 31 - Nov. 1. 2010.

Gígjukvísl
línurit
Data from a hydrometric station in the river Gígjukvísl Oct. 31 - Nov. 1. 2010.

Observations on the bridge over the river Gígjukvísl, which drains part of the glacier, confirmed a steady water level increase that indicated the onset of a jökulhlaup (see top part of graph). Measurements between 2 and 3 PM on Oct. 31 indicated a discharge of 143 m3/s (cubic meters per second) and the water was confined to a narrow part of the channel. Between 9 and 10 AM on November 1, the discharge had increased to 455 m3/s, filling most of the river channel underneath the bridge.

The automated hydrometric station at Gígjukvísl shows that the water level has increased by 1 metre during 20 hours (from 14 PM Oct. 31 to 10 AM Nov. 1). Since the floodwaters dig into the river bed, spread out and frequently change their course it must be kept in mind that the water level measured at a fixed location can only be viewed as an indicator of discharge. More extensive and repeated measurements at several places are therefore needed during jökulhlaups to determine the actual size of the flood.

The electric conductivity of the river water has increased considerably (see the lowest of the 3 graphs). This indicates that geothermal fluids originating in the volcanic system beneath Grímsvötn have mixed with the subglacial lake waters and now form a component of the floodwater.

The graph in the middle shows the water temperature (blue curve) and the air temperature (red curve). The water temperature is very close to the melting point whereas the air temperature curve reflects the diurnal variation.

An earthquake of magnitude 3.0 on the Richter scale occurred underneath the Grímsfjall mountain in Vatnajökull on the night before first indications of the jökulhlaup were observed. Grímsfjall is situated adjacent to the Grímsvötn subglacial lake (the source of the flood), and earthquakes and other tectonic movements associated with flooding are recorded by instruments on the mountain. Activity has subsided today.

Scientists will continue to monitor events in Grímsvötn and beneath Skeiðarárjökull very closely as the jökulhlaup progresses in the coming days, see additional information compiled during a sequence of events in 2004.

* Note: The Icelandic word jökulhlaup is widely used in the international geoscience literature for events of this kind; i.e. sudden outburst of floodwaters from subglacial or marginal lakes.




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