The Icelandic Met Office updated its Svartsengi bulletin on 28 April 2026 with a finding that demands attention: magma under Svartsengi has now exceeded 25 million cubic metres — the highest volume accumulated between eruptions since the Sundhnúkur crater row first awoke in November 2023.
The Magma Picture
According to IMO model calculations, more than 25 million cubic metres of magma have accumulated beneath Svartsengi since the last eruption ended in July 2025 — roughly nine months of slow, steady build-up. Uplift is continuing at approximately 2 centimetres per month, the slowest rate recorded across this entire eruption cycle.
A new InSAR satellite image covering the period 16 March to 18 April 2026 has just been received by the IMO. The image spans the entire Reykjanes Peninsula and shows a clear pattern: uplift is occurring only at Svartsengi. No deformation signals are visible anywhere else on the peninsula.
What InSAR shows: Interferometric Synthetic Aperture Radar compares satellite images taken at different times to detect tiny ground surface movements — down to millimetres. The fact that only Svartsengi shows uplift confirms that magma accumulation is localised there, not spreading to other volcanic systems on the peninsula.
Why Slow Doesn't Mean Safe
The IMO has been explicit about this since March: slow accumulation is not a sign that the eruption cycle is coming to an end. The comparison they keep returning to is the Krafla Fires — a sequence of 21 magma intrusions and eruptions on northeast Iceland between 1975 and 1984. During that cycle, the influx rate dropped significantly in the years before the largest and final eruption of the sequence in August 1984.
In other words, decreasing rate plus increasing volume is not a reassuring combination. It means more magma is present than at any previous trigger point, and the system has time to build further before the pressure is released.
The IMO is clear: no data suggests the eruption cycle on the Sundhnúkur crater row is ending. A magma intrusion toward the crater row leading to an eruption remains the most likely scenario. As before, warning time is expected to be between 20 minutes and just over four hours.
What the Seismicity Is Telling Us
Earthquake activity at Svartsengi remains low — most events are below magnitude 1. However, the IMO notes that seismicity appears to have increased slightly over the past two weeks. This is a pattern worth watching: in the lead-up to previous eruptions on the Sundhnúkur crater row, brief bursts of small earthquakes have preceded events by days to weeks.
The IMO is not currently assigning increased significance to this uptick — but it is monitoring it closely on a 24-hour watch basis and will update the hazard assessment immediately if the picture changes.
Hazard Assessment — Unchanged, Valid to 30 June
The current hazard map remains in force until 30 June 2026. The most likely eruption source, if one occurs, remains the zone between Stóra-Skógfell and Sýlingarfell — where previous intrusions and eruptions on the crater row have emerged. The IMO notes the potential rupture zone could be broader, extending from Grindavík in the south to an area northwest of Keili.
- Most likely scenario: A magma intrusion from Svartsengi toward the Sundhnúkur crater row, potentially resulting in an eruption
- Volume context: Previous eruptions have expelled between 12 and 31 million m³ from Svartsengi — the current store exceeds the lower end of that range
- Possible scale: Because stored volume is now the highest ever recorded between eruptions, the next event could be larger than previous ones if magma reaches the surface fully
- VALS level: Remains at 2 — Considerable Increased Activity (orange)
- No other signals elsewhere: InSAR confirms no deformation at any other volcanic system on the peninsula
For Grindavík residents and those in nearby areas: The IMO continues to advise that evacuation with short notice must remain a live possibility. Warning lead time has ranged from 20 minutes to just over four hours in previous events. Hazard zones and preparedness guidance are at vedur.is/eldfjoll.
The Bigger Picture: A System Under Pressure
This bulletin represents the latest chapter in a nine-month stalemate. Since the last eruption ended in late July 2025, Svartsengi has been quietly and steadily refilling. The IMO's models show that the magma volume has now never been higher between events — and yet the rate of arrival has never been slower.
That combination creates genuine scientific uncertainty. Slow accumulation makes it harder to predict precisely when the next intrusion or eruption will occur — the uncertainty window runs to several months. But the IMO's position is unambiguous: the uncertainty is about when, not if.
The 24-hour monitoring continues. Volcoholics will update this page as new bulletins are issued.