On September 1, a small glacial outburst flood began in Skaftá river from the western Skaftá ice cauldron, which generally produces smaller floods than the eastern one. While the smaller flood is now declining, the Iceland Meteorological Office expects a flood from the eastern cauldron to be starting, which will likely reach the route 1 road along the south coast tonight.
Yesterday, GPS measurements from Vatnajökull glacier showed that the surface of the ice cap over the Eastern-Skaftá cauldron had started to subside. It had dropped by just under 1m [3ft] the 12 hours since the process started but will likely drop by 60-100n [200-330ft] once the cauldron fully drains. That indicates that the glacial meltwater will drain, producing a glacial flood. The last flood from the Eastern-Skaftá cauldron occurred in August 2018.
The latest data suggest that floodwater from the eastern cauldron will reach the hydrological station at Sveinstindur tonight. Based on earlier floods, it will reach its peak just over 30 hours after that. The first signs of the flood are expected to reach lake Eldvatn during the night or early tomorrow morning. Once it does, the river’s flow will steadily increase and likely reach its peak by route 1, late Wednesday night or early Thursday morning.
Initially, the water flows along a 40km [25mi] long tunnel below the glacier and then for 28km [17mi] along Skaftá before it reaches the first hydrological station at Sveinstindur, which will provide data on the increase in water levels. Earlier floods from the Eastern cauldron have reached 3.000 m3/s [105,944 ft3/s] but the last one in 2018 peaked at 2.000 m3/s [70,629 ft3/s]. The current flood from the western cauldron peaked around midnight, September 2 at around 520 m3/s [18,363 ft3/s], and the river currently flows at 412 m3/s [14,549 ft3/s]. Based on experience from earlier floods, the floodwater will reach the first hydrological station today.
Based on the current amount of water in the cauldron, it’s likely that the flood will be of a similar size to the one that occurred in 2018 but water could spread further as last week’s smaller flood has raised the water level in the river.
The Met Office will continue to monitor this event closely.
Possible hazards
Locals and people travelling in the area should be aware of possible hazards and conditions there.
- In the next few days, Skaftá may overflow roads close to the river.
- High values of H2S are expected near Skaftárjökull and people are advised to stay at a safe distance from the river and nearby glaciers.
- Crevasses can form rapidly around the cauldron, so people travelling on Vatnajökull should stay away from the cauldrons and glaciers where floodwater is emerging.
Background information
The Skaftá cauldrons, eastern and western, are located in the western part of the Vatnajökull ice cap where geothermal activity melts the glacier from below and water accumulates beneath them. When the hydrostatic pressure is high enough for the water to lift the ice above it, the cauldron drains, causing a flood. Floods from the eastern cauldron are usually larger than the floods from the western cauldron. This phenomenon was first observed in 1955 and since then 58 floods have occurred. On average floods from each cauldron occur every two years.
The increase in electrical conductivity in the Skaftá river is probably due to steam explosions from the geothermal area beneath the ice cauldron. Steam explosions occur as the geothermal area adjusts to decreased water pressure resulting from the drainage of the cauldron. The explosions increase the amount of dissolved material in the floodwater, which is detectable downstream as conductivity increase in the river.
