Bárðarbunga has a habit of grabbing attention — and rightly so. Iceland's largest volcanic system by volume sits beneath Vatnajökull glacier and has a history that demands respect. Last night it reminded everyone it's still very much alive. The good news is that by this morning, the picture is clear: this was seismic, not volcanic.
What Happened
At 8:14 PM on 13 June 2026, a magnitude 4.8 earthquake struck the northeastern part of Bárðarbunga caldera. That single event triggered what the IMO describes as an intense earthquake swarm, which began in earnest around 10:00 PM. Approximately 400 earthquakes were measured over the following hours.
The swarm subsided rapidly after 3:30 AM on 14 June — a relatively short but sharp burst of activity concentrated in the caldera area. Since then, the IMO reports normal background seismicity at Bárðarbunga, consistent with what's typical for this system between significant events.
IMO verdict: No volcanic activity was measured during the swarm. The flight colour code, which was raised to yellow during the peak activity, has been lowered back to green. The situation is considered resolved for now, with standard monitoring continuing.
Why the Flight Code Was Raised — and Why It's Back to Green
Iceland's aviation colour codes are used to communicate volcanic risk to aircraft operators. When significant earthquake activity occurs at a volcanic system like Bárðarbunga, the code is raised as a precaution — not because an eruption is imminent, but because any rapid escalation could affect airspace with very little warning.
In this case, the swarm was intense enough to trigger a temporary elevation to yellow — meaning elevated unrest with potential for eruption. But crucially, none of the signals that would suggest magma movement appeared: no ground deformation, no volcanic tremor, no changes in gas emissions. With activity declining sharply after 3:30 AM and background levels restored by morning, the IMO lowered the code back to green.
What the codes mean: Green = volcano in normal, non-eruptive state. Yellow = volcano is exhibiting signs of elevated unrest. Orange = eruption is imminent or underway with minor or no ash. Red = major eruption underway with significant ash production. Bárðarbunga was yellow for a matter of hours before returning to green.
How Does This Compare to January 2025?
The IMO has noted that this swarm is similar in character to an earthquake swarm that occurred in the caldera in January 2025. That event followed a comparable pattern — a significant triggering earthquake, a burst of smaller events, rapid decline, no volcanic outcome. Bárðarbunga's caldera experiences periodic episodes of this kind as the system adjusts to ongoing stress from the 2014–15 eruption and continued subsidence of the caldera floor.
The 2014–15 Holuhraun eruption — the largest effusive eruption in Iceland in over 200 years — left Bárðarbunga in a state of slow but steady adjustment. The caldera dropped by around 65 metres during that event, and seismicity in and around it has remained elevated compared to pre-2014 levels ever since. Swarms like last night's are part of that ongoing adjustment.
Worth knowing: Bárðarbunga remains one of Iceland's most closely watched volcanic systems. A future eruption is a question of when, not if — though the timing is entirely unpredictable. When one does occur, it will most likely be effusive rather than explosive, but the subglacial setting means jökulhlaup (glacial outburst flood) risk is always part of the picture. Last night's swarm is not considered a precursor to imminent eruption.
What to Watch For
For now, there is nothing specific to monitor — the IMO's 24-hour watch at Bárðarbunga continues as normal at green status. If seismicity returns or intensifies, the flight code will be reassessed. The key signals that would indicate a shift toward volcanic unrest would be sustained tremor, ground deformation, or changes in the pattern of earthquake depths suggesting magma movement.
Volcoholics will update if the IMO issues any revised assessment for Bárðarbunga.