- The floodwaters are receding, with levels and conductivity in Skálm now nearing normal.
- The flood peaked the night before last.
- Experts from the Icelandic Meteorological Office (IMO) continue to monitor the situation closely.
The floodwaters in Skálm have begun to recede, as both water levels and conductivity are moving back toward their typical ranges, according to the latest updates from the Icelandic Meteorological Office. Seismic sensors stationed on nunataks in the Mýrdalsjökull ice cap confirm a significant drop in tremors over the past 24 hours, while a webcam at Rjúpnafell shows that the water volume in Leirá Syðri has decreased markedly since yesterday. This accumulating evidence suggests that the glacial outburst flood is coming to a close.
Figure 1: A visual representation of water levels in the Skálm river from July 5 to July 11 illustrates a notable rise beginning on July 8, as floodwater began entering the river.
Figure 2: This chart tracks changes in conductivity at Skálm during the same timeframe. The gauge at Leirá Syðri demonstrates a decline in conductivity; however, the water level is recorded at a higher mark. This discrepancy is likely due to sediment buildup in the river channel, which has temporarily increased the riverbed height and, accordingly, the water surface.
While the floodwaters decrease, residents and travelers in the area may still detect sulfur odors, prompting a word of caution to avoid riverbanks where gas pollution could linger.
Updated July 10, 2025
Overnight into July 10, both conductivity and water levels in Leirá Syðri and Skálm saw a gradual rise, continuing the trend of recent days. However, by early morning, both metrics began to decline, indicating that the peak at Leirá occurred on the evening of July 9, with Skálm following suit by the morning of July 10. Tremors recorded at Austmannsbunga have subsided and remain at low levels.
It appears that the flood will continue to recede, with discharge expected to return to normal summer levels. However, experts advise that unpredictable boiling in geothermal systems beneath the glacier could arise from depressurization following the flood, potentially leading to increased melting of glacier ice and subsequent flooding.
The full implications of these developments remain uncertain, and the Icelandic Meteorological Office will maintain its 24-hour monitoring operations to keep a close watch on the situation.
Figure 1: Graphically captures the fluctuation of water levels in upper Leirá Syðri from July 7 to 2 p.m. on July 10.
Probable Origin of the Flood
Experts suspect that the flood originated from geothermal cauldrons beneath Mýrdalsjökull, specifically south of Austmannsbunga (noted as cauldrons 13 and 14 in the Kötlukettle numbering system). These are the same cauldrons that triggered a substantial flood last July. Ice radar data collected by Eyjólfur Magnússon at the University of Iceland’s Institute of Earth Sciences in May indicates a significant accumulation of water beneath these cauldrons. While this reservoir may be behind the current flood, definitive evidence of a drop in the glacier’s surface level has yet to be confirmed, leaving room for further investigation. Remote sensing data in the upcoming days, alongside pilot reports from aerial surveys, could provide additional insights.
Figure 2: A map illustrating the placement of monitoring instruments around Mýrdalsjökull and the course of Leirá Syðri in Skálm.
Reports of Sulfur Odors and Travel Advisories
The Icelandic Meteorological Office has received multiple reports of sulfurous odors in the vicinity of Skálm. Travelers are urged to exercise caution near the rivers, as gas pollution may be present. A general sense of caution is also warranted near river channels.
Since July 8, nearly 100 earthquakes have been logged in Mýrdalsjökull, with the most significant measuring 2.7 in magnitude at 7:00 a.m. on July 10. Larger seismic activities remain a possibility, warranting vigilance in and around the glacier.
Figure 3: Specialists from the Icelandic Meteorological Office measuring conditions at Skálm on July 9. (Photo: Njáll Fannar Reynisson.)
Additional Observations in Fremri-Emstruá
Elsewhere, reports indicate rising water levels in Fremri-Emstruá, though this event appears unconnected to the current situation in Leirá and Skálm. Such floods are seasonal occurrences, typically seen between late June and early August, and usually do not inflict damage apart from potential gas emissions near the riverbed as glacier runoff increases. Travelers should remain cautious around Fremri-Emstruá and along the edges of Entujökull.
Updated July 9, 2025
In recent days, measurements from a new monitoring instrument near Sandfellsjökull indicate a rise in both water levels and conductivity in Leirá Syðri. Elevated levels are also evident at the bridge over Skálm on Highway 1, where Leirá Syðri flows into Skálm upstream. As of now, this situation is categorized as a minor flood event, although monitoring continues as water levels and conductivity gradually rise.
The presence of sulfur odors has led the Icelandic Meteorological Office to advise people to be cautious near the river’s source, where gas pollution could affect air quality. Those near river channels are reminded to take necessary precautions.
The 24-hour monitoring by the Icelandic Meteorological Office is ongoing, with further updates to follow as the situation evolves.
Development of Water Levels in Upper Leirá Syðri from July 7 to 3 p.m. on July 9.
Variable Size of Glacial Floods from Mýrdalsjökull into Leirá
Floods stemming from geothermal regions beneath the glacier are known to affect several rivers around Mýrdalsjökull, including Múlakvísl and Fremri-Emstruá. Historically, Leirá has experienced varying flood sizes; from 1995 to 2000, annual floods were common, alongside a small flood in 2012 that caused minimal disruption beyond sediment deposition at the Leirá alluvial fan south of Sandfell.
Last summer, a minor flood occurred at the end of July, but it was followed by an unexpected major flood that inundated Highway 1 and resulted in structural damage. This was traced back to two cauldrons in Mýrdalsjökull south of Austmannsbunga, formed by geothermal melting at the glacier’s base.
Since that major flooding event, four smaller floods have transpired in the river, none of which caused damage. The most recent minor flood occurred in December.
Bergur Einarsson, Head of Hydrology at the Icelandic Meteorological Office, emphasized, “The causes of last year’s catastrophic flooding remain unclear. If depressurization in the geothermal systems beneath the glacier caused the previous flood, we must be cautious, as similar occurrences could occur with the current situation.” He added, “Recent radar measurements indicate there may already be significant water accumulation at the glacier bed.”