Fissure Eruptions Explained: When the Ground Splits Open
Not all eruptions come from a single crater at the top of a cone. Some of the most voluminous eruptions in Earth's history have poured lava from long cracks in the ground, where the crust splits open and magma wells up along a line. These fissure eruptions can produce spectacular curtains of fire, vast lava plains, and, in the geological past, outpourings so immense they reshaped the climate. They are the signature of rifting and the engine behind some of the planet's greatest volcanic events.
What a fissure eruption is
A fissure eruption occurs when magma reaches the surface along a crack, or fissure, rather than through a single central vent. Lava emerges along the length of the fissure, often beginning as a line of lava fountains before concentrating into a few vents. This style is typical of fluid basaltic magma and of the rift zones where the crust is being pulled apart.
Curtains of fire
In the opening phase of a fissure eruption, lava can fountain along the entire length of the crack, creating a dramatic curtain of fire, a continuous line of incandescent fountains stretching across the landscape. This spectacular phenomenon is often short-lived, as the eruption soon concentrates into a few stronger vents, but it is one of the most striking sights in volcanism.
Building lava plains and shields
Fissure eruptions produce fluid lava that can flow far across the land, building broad lava plains and contributing to the growth of shield volcanoes. In Iceland and Hawaii, fissures on the flanks and rift zones of volcanoes feed flows that have repeatedly reshaped the landscape. The 2014-2015 Holuhraun eruption in Iceland and the recent Fagradalsfjall eruptions are modern examples of fissure activity.
Flood basalts: the greatest eruptions
In the geological past, fissure eruptions on an almost unimaginable scale produced flood basalts, vast outpourings of lava that covered hundreds of thousands of square kilometres. Provinces such as the Deccan Traps of India and the Siberian Traps record these colossal events, some of which released so much gas that they are linked to mass extinctions and major changes in Earth's climate.
Fissures and rifting
Fissure eruptions are intimately tied to rifting, where tectonic forces pull the crust apart. As the crust stretches and cracks, magma rises to fill the gaps, erupting along fissures. This is why fissure eruptions are characteristic of Iceland, which straddles the Mid-Atlantic Ridge, and of the East African Rift, where a continent is slowly splitting apart.
The hazards of fissure eruptions
Although often less explosive than eruptions from steep cones, fissure eruptions carry their own hazards. Fluid lava flows can travel quickly and cover large areas, burying land and infrastructure, as seen at La Palma in 2021. Large fissure eruptions can also release enormous quantities of gas, which, as the 1783 Laki eruption showed, can prove deadly far beyond the volcano itself.
Reading the rift
For geologists, fissure eruptions and their deposits reveal the workings of rift zones and the behaviour of fluid basaltic magma. The alignment of vents, the extent of lava flows, and the structure of fissure systems all help scientists understand how the crust is splitting and how magma moves beneath it, knowledge vital for forecasting future eruptions in rift settings.
Explore on the map
From the fissures of Iceland and Hawaii to the rift volcanoes of East Africa, fissure eruptions shape some of the most dynamic volcanic landscapes on Earth. Explore them on the interactive map — filter by region to see where the ground splits open and lava pours from the cracks in the Earth's crust.