What Is a Fissure Eruption?
Picture magma rising not up a single pipe but along a thin vertical sheet of rock — a dike. When that sheet reaches the surface, it doesn't erupt from one point; it erupts along its entire top edge at once. The result is a line of lava fountains, sometimes only a few meters apart, that geologists call a curtain of fire. Early on, the whole fissure may be active; within hours or days, activity usually focuses down to a few points where spatter cones build up.
The reason fissures matter is where they happen. At divergent plate boundaries — where the crust is being stretched and pulled apart — magma naturally rises as dikes, so fissure eruptions are the defaultway lava reaches the surface. Iceland, which sits directly on the Mid-Atlantic Ridge, is the world's showcase for them. The same thing happens along the rift zones that flank fluid shield volcanoes like Kīlauea.
Iceland 2023–2026: The Sundhnúkur Fissure Crisis
The best modern example of a fissure eruption is happening now. Since December 2023, the Sundhnúkur crater rowon Iceland's Reykjanes Peninsula has erupted nine times through mid-2025, each time opening a fresh fissure across the same stretch of ground between Sundhnúkur and Stóra-Skógfell. The fishing town of Grindavík was evacuated, the famous Blue Lagoon spa has repeatedly closed, and lava has threatened the Svartsengi geothermal plant that heats much of the peninsula.
Status — July 2026
No fissure is erupting in Iceland at the moment, but the IMO reports that roughly 26.6 million m³ of magmahas re-accumulated beneath Svartsengi since the last eruption — more than before any previous event in the series. Another Sundhnúkur fissure eruption is described as "the most likely scenario in the coming weeks." Track it on our Iceland volcano page.
The Sundhnúkur eruptions are textbook fissure behavior: magma collects in a reservoir under Svartsengi, pressure builds, and when it exceeds the strength of the overlying crust it lances sideways and up as a dike, breaking the surface as a curtain of fire in a matter of hours. Warnings come with very little lead time — often under an hour.
Kīlauea 2018: 24 Fissures in a Neighborhood
Fissure eruptions aren't just an Icelandic story. In May 2018, Kīlauea's Lower East Rift Zone tore open beneath the Leilani Estates subdivision in the Puna district of Hawaii. Over the following weeks, 24 separate fissures opened across residential streets, and lava from one of them — Fissure 8 — flowed all the way to the sea, destroying more than 700 homes before the eruption ended in September.
Kīlauea has 75 recorded eruptionsin our Smithsonian catalog, and its two rift zones make it one of the most reliable fissure-producing volcanoes on Earth. The 2018 event is the clearest demonstration of why fissure eruptions are dangerous even when they aren't explosive: it's the lava volume and the fact that the crack can open exactly where people live.
Laki 1783: The Fissure Eruption That Changed History
To understand the true scale a fissure can reach, look at Laki. In June 1783, a 27 km-long fissure in the Grímsvötn volcanic system of southern Iceland began an eruption that lasted eight months and poured out roughly 15 cubic kilometers of lava — the largest lava flow in recorded human history.
The lava itself killed almost no one directly. The gas did. Laki released an estimated 120 million tonnes of sulfur dioxide plus enormous amounts of fluorine, which settled onto grass and poisoned livestock. In the resulting famine — the "Móðuharðindin," or Mist Hardships — about a quarter of Iceland's population died. A sulfurous "Laki haze" spread across Europe, causing thousands of deaths in England that summer and bitter cold the following winter. Some historians argue the crop failures it triggered in France helped set the stage for the French Revolution. It is the deadliest fissure eruption in the historical record, and a reminder that a "gentle" effusive eruption can still be catastrophic.
Fissure Eruptions vs Other Eruption Types
Where a fissure eruption sits among the main eruption styles — it trades explosive violence for sheer lava volume:
| Eruption Type | Vent | Explosivity | Lava Output | Example |
|---|---|---|---|---|
| Fissure (Icelandic/Hawaiian) | Linear crack, often km long | Low | Very high lava volume | Laki 1783, Holuhraun 2014 |
| Hawaiian | Central vent or short fissure | Low | High, fluid lava | Kīlauea summit |
| Strombolian | Single vent | Mild, rhythmic | Moderate | Stromboli |
| Plinian | Single central conduit | Extreme | Huge ash column, little lava | Vesuvius 79 AD |
For the explosive end of the spectrum, see our guide to the Plinian eruption; for how these compare to eruptions that build a single cone, see central volcanoes.
Frequently Asked Questions
What is a fissure eruption?
A fissure eruption is when lava erupts from a long, narrow crack in the ground — a fissure or fissure vent — rather than from a single central crater. Magma rising along a vertical sheet of rock (a dike) reaches the surface all along its length at once, producing a wall of lava fountains often called a 'curtain of fire.' Fissure eruptions are the main way lava reaches the surface at divergent plate boundaries like Iceland's.
Are fissure eruptions dangerous?
They are usually less explosive than eruptions from a single vent, but they are not harmless. Fissures produce enormous volumes of fast-moving lava that can overrun roads, farmland, and towns — as in Kīlauea's 2018 eruption, which destroyed over 700 homes. The greater long-term danger is gas: the Laki fissure eruption of 1783 released so much sulfur dioxide and fluorine that it killed about a quarter of Iceland's population and caused crop failures across Europe.
What causes a fissure eruption?
Fissure eruptions happen where the crust is being pulled apart. As plates rift, magma intrudes as a thin vertical sheet called a dike; if that dike reaches the surface, it erupts along its whole length as a fissure. This is why they dominate at divergent boundaries and rift zones — Iceland's Mid-Atlantic Ridge, the East African Rift, and the rift zones flanking shield volcanoes like Kīlauea.
Where do fissure eruptions occur?
Most occur along divergent plate boundaries and volcanic rift zones. Iceland sits astride the Mid-Atlantic Ridge and is the classic setting — its Sundhnúkur crater row has erupted repeatedly from 2023 through 2025. Hawaii's Kīlauea has two rift zones that regularly open fissures, and large basaltic lava provinces like the Columbia River Basalts were built by ancient fissure eruptions on a colossal scale.
What is the difference between a fissure eruption and a normal eruption?
A 'normal' cone-building eruption erupts from a single central vent and tends to build a mountain over time. A fissure eruption erupts from a line, so instead of a cone you get a row of small spatter cones and vast, flat lava flows. Fissures generally release more lava but less explosive energy than central-vent eruptions of the same magma volume.