There are no indications from the Norwegian Meteorological Agency’s data that subglacial eruption caused the glacier flood. Although this runoff was unusually large, it was due to geothermal heat in the glacier’s cauldrons, causing meltwater to accumulate and then surge ahead of the glacier. A GPS meter on Austmannsbunga shows clear signs that the changes measured in the caldera are from a regular glacier run. However, the reason for the release of more water than usual from such runs remains unclear.
This afternoon, the Coast Guard conducted a flight with scientists from the Icelandic Meteorological Office and the University of Iceland to investigate the situation. During the flight, it was confirmed that the runoff originated only from Sandfellsjökull and flowed into the river Skálm. There was no visibility over Mýrdalsjökull to determine which cauldrons the water was coming from.
Satellite images show subsidence in the well-known caldera on Mýrdalsjökull. It is estimated that about 2 million cubic meters of water must accumulate in Mýrdalsjökull’s cauldrons before it flows out. Based on initial estimates, the size of the run in Skálm was many times larger than a typical run.
The water level and electrical conductivity in Skálm have decreased significantly since yesterday. The effect of the runoff from Sandfellsjökull on the eastern side of Mýrdalsjökull, which started yesterday, continues to diminish. There are no signs of running water in Jökulsá at Sólheimasandi or Múlakkísl.
The low seismic activity was recorded under the glacier last night. This morning, several earthquakes were noted, the largest with a magnitude of M 2.9 around 6:00 AM local time. There was no subsequent increase in the volcanic unrest.
Signs of ice turbulence were detected at Godabunga on the west side of Mýrdalsjökull last night. The unrest originated in the same area as the morning’s earthquake activity. Electrical conductivity and water flow in Markarfljót, west of Mýrdalsjökull, have slightly increased over the last 24 hours. A small amount of the runoff water is reaching Markarfljót from Entujökli on the west side of Mýrdalsjökull, but considering last night’s turbulence, this water will not pose any danger to the area.
If no further seismic activity or runoff turbulence is measured, no additional runoff from Mýrdalsjökull is expected at this time. However, the National Weather Service continues to closely monitor the area. It should be noted that it may take several days for the flow in Skálm to return to normal for this time of year. As occurred after the large run in Múlakvísl in 2011, high activity with seismic events and frequent smaller glacier runs can be expected from Mýrdalsjökull this year.
Source: Icelandic Met Office volcano activity update 29 July 2024
