- The flood is receding, with water levels and conductivity in Skálm nearing normal readings.
- The flood peaked the evening before last.
- Specialists from the Icelandic Meteorological Office are continuing their observation in the area.
In the last 24 hours, the water levels at the Icelandic Meteorological Office’s gauging station in Skálm, situated by the highway, have shown a promising decline, drawing closer to their normal values. Simultaneously, seismic sensors placed on nunataks in the Mýrdalsjökull ice cap indicate a significant reduction in tremors. A live feed from Rjúpnafell reveals that the water volume in Leirá Syðri has also notably decreased since yesterday, signaling the gradual end of the glacial outburst flood.
Figure 1: Water level variations in the Skálm River alongside the highway over the past week (July 5–11). The upward trend began on July 8 as floodwaters began pouring into the river.
Figure 2: Conductivity levels in Skálm by the highway over the last week (July 5–11).
While there’s a decrease in conductivity at Leirá Syðri, the water levels show a rise, likely due to sediment buildup in the river’s channel. This accumulation elevates the riverbed, resulting in higher measurements for the water surface.
Residents and travelers may still experience a sulfur smell in the region and are urged to tread carefully near the rivers.
Updated July 10, 2025
Overnight into July 10th, conductivity and water levels in Leirá Syðri and Skálm saw an increase, following the recent upward trend. By the morning of July 10th, both metrics began to drop, indicating that the peak in Leirá occurred on the evening of July 9th, while Skálm reached its peak at the Highway 1 bridge on July 10th. Notably, the seismic tremors at Austmannsbunga have also diminished since the morning of July 10th, and remain low.
It appears that the flood will continue to decline, with discharge expected to revert to typical summer levels. However, there remains a possibility of sudden boiling in geothermal systems beneath the glacier, triggered by depressurization from the flood, which could lead to further melting of glacial ice and increased runoff.
At this point, predictive capabilities regarding further developments remain uncertain. Continuous 24-hour monitoring from the Icelandic Meteorological Office is in effect as they diligently track the situation.
Figure 1: Water levels in upper Leirá Syðri from July 7 to 14:00 on July 10.
Possible Origins of the Flood
The current flood likely stems from geothermal cauldrons situated in Mýrdalsjökull, south of Austmannsbunga (specifically, cauldrons 13 and 14 in the Kötlukettle numbering system). These same cauldrons were responsible for a significant flood in July of last year. Recent ice radar measurements, conducted in May by Eyjólfur Magnússon from the Institute of Earth Sciences at the University of Iceland, suggest substantial water accumulation beneath these cauldrons at the glacier’s base, potentially explaining the current events. However, no confirmation has been received regarding any changes to the glacier surface in these areas, leaving the situation somewhat uncertain. Data from remote sensing in the coming days may shed more light, as will pilot reports from flights over the region.
Figure 2: Map illustrating the locations of monitoring instruments around Mýrdalsjökull and the path of Leirá Syðri in Skálm.
Notices of Sulfur Odors and Travel Advisories
The Icelandic Meteorological Office has received reports of sulfur odors near Skálm. Travelers are urged to remain cautious near the rivers, as gas pollution may be a concern. It is paramount to exercise care whenever near river channels.
Since July 8, nearly 100 earthquakes have been recorded in Mýrdalsjökull, the largest registering a magnitude of 2.7 at 7:00 AM on July 10. The potential for larger seismic activity remains, making caution essential in the glacier vicinity.
Figure 3: Specialists from the Icelandic Meteorological Office conducting measurements at Skálm on July 9. Photo: Njáll Fannar Reynisson.
Additional Observations in Fremri-Emstruá
Alongside the flooding in Leirá and Skálm, there are also reports of floodwaters in Fremri-Emstruá. This seems to be an independent incident, as similar floods in this river are commonplace during the late June to early August timeframe. Historically, these floods have not led to damage or significant hazards, aside from possible gas emissions near the glacier’s riverbed. Therefore, travelers are also warned to maintain caution near Fremri-Emstruá and the edge of Entujökull.
Updated July 9, 2025
Recent measurements from a new monitoring instrument in front of Sandfellsjökull indicate rising conductivity and water levels in Leirá Syðri. Elevated levels are also evident at the Highway 1 bridge over Skálm, as the former flows into the latter upstream.
At this stage, this event is categorized as a minor flood, although water levels and conductivity are still gradually escalating.
Reports of sulfur odors have prompted the Icelandic Meteorological Office to call for caution near the river source, as gas pollution may still be present in the area. Travelers should consistently exercise caution near river channels.
The Icelandic Meteorological Office will continue to monitor the situation closely and will provide further updates as developments unfold.
Water Level Changes in Upper Leirá Syðri from July 7 to 15:00 on July 9.
Diverse Sizes of Glacial Floods from Mýrdalsjökull into Leirá
Floods of this nature, originating from geothermal zones beneath the glacier, are not uncommon across several rivers in the Mýrdalsjökull region, including Múlakvísl and Fremri-Emstruá.
Historically, Leirá has experienced floods of varying magnitudes. Between 1995 and 2000, annual floods were noted, along with a minor occurrence in 2012. These events typically resulted in no significant damage, aside from sediment deposition that built up the Leirá alluvial fan south of Sandfell, eventually redirecting the river’s southern channel.
Last summer, a minor flood similarly struck Leirá Syðri and Skálm at the end of July, which unexpectedly escalated to a major flood that overflowed and damaged parts of Highway 1. This sizable flood traced its origins to two cauldrons located in Mýrdalsjökull.
Since the substantial July 2024 flood, there have been four smaller floods in the river, none leading to damage, with the last recorded in December.
“The precise causes of last year’s major flood remain elusive,” notes Bergur Einarsson, Head of Hydrology at the Icelandic Meteorological Office. “If boiling in geothermal systems beneath the glacier—triggered by a minor glacial flood—was indeed responsible for the major flood last year, then current events could similarly result in an escalation of flooding. We must also remain vigilant, as recent ice radar measurements show substantial water accumulation at the glacier’s base,” he adds.
