The Volcanoes That Never Stop

Most volcanoes spend almost all of their existence doing nothing. They build up pressure over centuries, release it in a few violent days, and go back to sleep. That is the normal pattern, and it is why volcano tourism is mostly a tourism of landscapes rather than of eruptions.

Then there is a small group that behaves in the opposite way. They erupt more or less constantly, at a modest scale, for decades. Stromboli has been at it since February 1934. Dukono, in eastern Indonesia, since 13 August 1933. Yasur, in Vanuatu, since roughly 1270, which means it was already going when the last of the medieval Icelandic eruptions were burning out.

These are the volcanoes worth planning a trip around, because they are the only ones with any claim to reliability.

The scientific literature calls these systems open-vent volcanoes. The name is mechanical rather than descriptive: the conduit between the magma reservoir and the surface stays open, so gas escapes continuously instead of accumulating until something breaks.

The category was defined around a puzzle. In 1993 a paper in Nature pointed out that persistently active volcanoes emit far more gas than the volume of erupted magma can account for. Enormous quantities of sulphur dioxide come out, while comparatively little lava does. The magma degasses at depth, the gas rises independently, and most of the degassed magma never reaches the surface at all. It sinks back down.

You do not need the geochemistry to travel well, but one consequence matters. An open vent is a pressure release valve, and a valve that is working is safer than one that is stuck. The dangerous moment at these volcanoes is not the routine activity. It is when the routine stops.

Below are the longest-running eruptions on earth. The second column is the one that matters to a traveller, and it is where the romance drains out of the subject.

Read that column again and the picture is stark. Of fifteen of the most persistently active volcanoes on the planet, four are genuinely visitable: Stromboli, Yasur, Masaya, and Santiaguito from a distance. Add Fuego, which you watch from its neighbour. That is the whole list.

The most dependable volcanic activity in the world is happening in Antarctica, in Bougainville, and on an Indonesian island most Indonesians could not point to. Reliability and reachability turn out to be almost unrelated.

If you compare lists of long-running eruptions across different sources you will find the start dates disagree, sometimes by decades. This is not sloppiness. It is the counting rule.

An eruption is treated as ongoing until there is a gap of three months or more. Once that gap happens, the clock resets, even if the volcano wakes up again in month four and behaves exactly as before. So Sakurajima, which has been one of the busiest volcanoes in Japan since the 1950s, carries a start date in 2017. Semeru has been erupting on and off since the 1960s and carries 2019.

The practical lesson: a start date tells you about the current unbroken run, not about the volcano's character. For planning, the character is what you want. Sakurajima has produced hundreds of explosions a year for decades and will keep doing so regardless of which date the catalogue shows this season.

A lava lake is the only volcanic phenomenon that is genuinely continuous rather than merely frequent. Molten rock, in the open, all the time. There have never been more than about eight in the world simultaneously, and the membership changes.

Two disappearances are worth knowing about, because they show how fast this can happen. In December 2018 the twin lakes at Benbow and Marum, on Ambrym in Vanuatu, drained in a single event when a dyke of roughly 0.7 cubic kilometres of magma propagated more than twenty kilometres along the island's rift zone and emptied the system beneath them. Two of the most photographed lava lakes on earth, gone in a night, and they have not returned.

Nyiragongo in the Democratic Republic of the Congo held the largest of them, above the city of Goma. The 2021 eruption destroyed it, killed 32 people and levelled 17 villages. The lake has since reformed. What keeps travellers away now is not the volcano.

Masaya's lake, which formed in December 2015, has been weakening since 2017. It is still the easiest lava lake in the world to reach, and I would not assume it will be there in ten years.

Three practical conclusions come out of all this.

Prefer persistence over fame. A famous volcano that erupts once a decade is a worse bet than an unglamorous one that erupts every twenty minutes. Stromboli is not on many bucket lists and it outperforms almost everything that is.

Check what closes it, not what opens it. For these volcanoes the activity is not the variable. Access is. Find out who sets the alert level, what level closes the summit, and where that number is published, before you commit to dates.

Go sooner. This is the one piece of urgency in this whole subject that I think is honest. Lava lakes drain. Dome complexes stabilise. Arenal ran for 42 years and then stopped in a matter of months. Nothing here is permanent, and the ones that have been going longest have, by definition, been going a long time.