What Happened in April 2010
Eyjafjallajökull is a 1,651-metre stratovolcano in southern Iceland, capped by a glacier — the name means “island-mountain glacier” in Icelandic. After a smaller flank eruption at Fimmvörðuháls in late March, the main summit eruption began on 14 April 2010, directly beneath the ice cap. Meltwater poured into the vent, flash-chilling and shattering the rising magma into enormous quantities of fine, glassy ash. A plume climbed to around 9 kilometres and the prevailing winds carried it southeast — straight over the most heavily trafficked airspace on the planet.
Within a day, Europe started closing its skies. What followed was less a natural disaster than a logistical one: no deaths, no flattened towns, but millions of people stranded in airports from Beijing to Boston because a glacier-capped volcano in the North Atlantic was quietly making the wrong kind of ash.
Why a Mid-Size Eruption Grounded 100,000 Flights
Fine volcanic ash doesn't just dirty a jet engine — it melts inside the combustor, around 1,000 °C, then re-solidifies as glass on the turbine blades and can flame out the engine in minutes. That single fact is why the response was total closure rather than rerouting. The volcanic ash from Eyjafjallajökull was especially dangerous: glacial meltwater had fragmented it into particles fine enough to stay aloft for days and spread across a continent, and jet engines have no tolerance for it (USGS).
The scale, from IATA and the official tallies compiled afterward: about 95,000 flights cancelled during the six-day ban (roughly 107,000 over the full eight-day event), accounting for around 48% of normal air traffic and roughly 10 million passengers; more than 300 airports in about two dozen countries closed; and an estimated US$1.7 billion in lost revenue to airlines, burning roughly US$200 million (£130 million) a day at the peak. The main closure ran 15–23 April 2010, the largest shutdown of European air traffic since the Second World War (Wikipedia summary of the disruption).
How Big Was It, Really?
Here is the part the headlines missed. On the Volcanic Explosivity Index, Eyjafjallajökull 2010 scored a VEI 4 — real, but unremarkable. Compare it to the eruptions on our most explosive volcanoes list: Pinatubo in 1991 was VEI 6 — about a hundred times larger — and Tambora in 1815 was VEI 7, the kind of eruption that chills the whole planet. Neither closed a continent's airspace for a week. Eyjafjallajökull did, with a fraction of the power.
It wasn't even Eyjafjallajökull's own ceiling. Its recorded history is short but telling — and the right-hand column is the detail almost nobody connects.
| Eruption | VEI | Did Katla follow? | Notes |
|---|---|---|---|
| 2010 CE | 4 | No (so far) | The eruption that closed European airspace. Katla has not followed in the 16 years since — the exception to the historical pattern. |
| 1821–1823 CE | 2 | Yes — Katla 1823 (VEI 3) | A long, intermittent eruption; Katla erupted during it, in 1823. |
| 1612 CE | 2 | Yes — Katla 1612 (VEI 4) | Followed closely by a Katla eruption the same year in our record. |
| 920 CE | 3 | Yes — Katla 920 (VEI 4) | The oldest well-dated eruption; paired with a Katla event. |
| 550 CE | — | Unknown | Earliest eruption in the record; VEI not assigned. |
Source: VolcanoDB analysis of Smithsonian Global Volcanism Program records for Eyjafjallajökull (GVP #372020, 5 recorded eruptions) and Katla (GVP #372030). See the Eyjafjallajökull data page and the eruption timeline.
The Katla Problem — What Usually Comes Next
Cross-reference our eruption records for Eyjafjallajökull against those of its neighbour Katla and a pattern jumps out: three of Eyjafjallajökull's four well-dated eruptions — 920, 1612 and 1821–23 — were each matched by a Katla eruption (920, 1612 and 1823 in our GVP record). Historians and the Icelandic Met Office have long noted the pairing. Katla is the bigger, more dangerous volcano of the two: it sits under the thick Mýrdalsjökull ice cap, and its eruptions can trigger jökulhlaups — glacial outburst floods — and far larger ash columns than 2010.
The 2010 eruption is the fourth in that sequence — and so far, the exception. Katla has not erupted since 1918, through more than a century that includes the 2010 event. That is worth stating plainly in both directions: the historical link is real and it is in our data, but it is an observation, not a prediction. Katla is one of the most closely watched volcanoes in the world, and as of 2026 it has given no sign of an imminent eruption. If it ever does break its silence, Iceland's wider volcanic activity — already busy with the Reykjanes fissures — is where the next chapter gets written.