Volcanoes attract stories the way they attract photographers, and the stories are not all equally sturdy. Several of the best-known facts about famous eruptions turn out, when you follow them back, to be a misreading of a table, a number that could not have been measured with the instruments of the time, or a marketing invention from the 1940s.
So everything here carries a label. Fact means documented, and we found the documentation. Disputed means specialists genuinely disagree. Legend means it is repeated everywhere and it is not true.
The legends are the more entertaining half.
Things you can see
Pumice floats. It is the only common rock that does, because it is solidified lava foam with more void space than solid. After a submarine eruption, rafts of it drift across the ocean for months. Fact.
The blue fire at Ijen is not lava. It is sulphurous gas igniting on contact with air, together with molten sulphur burning as it runs downhill, with flames reaching five metres. Visible only in darkness, which is why tours leave at one in the morning. In daylight it looks like an ordinary crater. Fact.
Ijen's crater lake is the largest acidic lake in the world by volume, 950 metres across and 182 metres deep, and it is a brine of sulphuric and hydrochloric acid. Fact.
Its pH is usually quoted as around 0.3, but published measurements range from 0.02 to 0.5 depending on how agitated the volcano is. Any single number is a snapshot. Disputed.
Papakolea beach in Hawai'i is green because olivine crystals in the surrounding tuff ring are denser than the ash holding them, so the waves carry the light material away and leave the green mineral behind. Fact.
Pele's hair is real glass. Wind stretches airborne lava droplets into golden threads five to fifteen centimetres long and as fine as a human hair. It travels kilometres downwind, embeds in skin, needs gloves to handle, and contaminates rainwater tanks. Fact.
Kazumura Cave on Hawai'i is the longest and deepest lava tube on earth, at 65.5 kilometres with 1,101 metres of vertical range, formed about five hundred years ago. Fact.
The ground at Timanfaya on Lanzarote is between 100 and 600 degrees at thirteen metres depth, almost three centuries after the eruption that made it. The park restaurant grills food over an open pit using nothing else. Fact.
Dinner, cooked by the planet
Four cuisines, one heat source
People have been putting food in volcanic ground for centuries
At Furnas in the Azores, the cozido goes into a pot, the pot goes into a hole dug in the hot ground beside the lake, and it comes out five or six hours later. The restaurants have their own numbered holes and the extraction draws a crowd. Fact.
At Whakarewarewa in New Zealand, Maori communities cook with steam and boiling pools directly. Worth distinguishing from the classic hangi, which is an earth oven heated with fire-heated stones and involves no volcano at all. Fact.
Icelandic rye bread baked in the ground beside a hot spring is called hverabraud. Its nickname translates as thunder bread, and the name refers not to the volcano but to the effect on the digestion. Fact.
The black eggs of Owakudani in Japan turn black because sulphur in the water reacts with iron and deposits dark compounds on the shell. That each one adds seven years to your life is offered locally as tradition rather than as chemistry. Legend, and cheerfully so.
Wine, and the insect that could not cross sand
What stopped phylloxera was not volcanic soil but sandy texture. The louse cannot move through sand with no clay in it. On Etna the clay content is under three per cent, and at Colares in Portugal vines survived on three to four metres of sand that is not volcanic at all. The volcano is a coincidence of texture. Fact.
Santorini's vines are ungrafted and trained into ground-level baskets, with the grapes on the inside, to shelter them from wind and sun. Fact.
At La Geria on Lanzarote each vine sits in a pit four to five metres wide and two to three deep, behind a crescent wall, in ash that condenses the night dew. The island receives about 100 millimetres of rain a year. Fact.
The Timanfaya eruptions of 1730 to 1736 created 32 volcanoes along 18 kilometres, buried a quarter of Lanzarote and eleven villages, and drove emigration that contributed to the founding of San Antonio in Texas in 1731. Fact.
Etna was Sicily's first protected wine denomination, established in August 1968, with vineyards between 400 and 1,100 metres. Fact.
Numbers that sound invented
| The claim | The detail |
|---|---|
| Lava reached 60 km/h | Nyiragongo in 1977. Its lava is so low in silica that when the lava lake drained in under an hour, the flow moved faster than anything else recorded |
| A volcano flooded 13 per cent of a city | Nyiragongo again, in 2002: 4.7 square kilometres of Goma, around 245 dead and 120,000 homeless |
| The Blue Lagoon is industrial waste water | It is the outflow of the Svartsengi geothermal plant. The silica that gives it the colour also seals the porous lava floor, so new pools have to be excavated |
| Iceland runs on volcanoes | 99.9 per cent of its electricity is hydro and geothermal, and around 90 per cent of homes are geothermally heated. Most of that electricity goes to heavy industry |
| One eruption cancelled 104,000 flights | Eyjafjallajokull in 2010: 48 per cent of expected European traffic over eight days, peaking at 80 per cent, with around 10 million passengers stranded |
| One region gained air traffic in 2010 | The Azores, which handled the transatlantic flights diverted around the ash |
| An island was closed the year it was born | Surtsey emerged in November 1963 and was declared a reserve in 1965, while still erupting, to protect the ecological succession. It has shrunk from 2.7 to 1.3 square kilometres |
| A tomato plant caused a scientific incident | On Surtsey, a badly managed human defecation produced a tomato seedling, which was destroyed |
| A beach has killed six people since 2007 | Reynisfjara in Iceland, where sneaker waves have caused at least twelve emergency responses and six deaths |
Pompeii, more precisely than usual
The wave that killed the most people at Pompeii left a deposit three centimetres thick. It killed around 650 people and passed in somewhere between thirty seconds and two and a half minutes. Being buried is not what did it. Fact.
Herculaneum was buried under twenty metres and was nearly empty. Its population had reached the shore, where roughly three hundred skeletons have been found in the boat chambers, in places three to a square metre. Fact.
The two cities died differently because of temperature. The currents reaching Herculaneum were around 500 degrees; those reaching Pompeii between 180 and 380. That difference is why the two sites look so unalike today. Fact.
The date of 24 August is probably wrong. It comes from a printed copy of Pliny made in 1508. Pomegranates, heavy clothing, sealed wine jars and the direction of the debris all point to autumn, and in 2018 a charcoal inscription dated to 17 October was found at the site. Disputed, and moving.
In March 1944 Vesuvius destroyed 88 American bombers at the Pompeii airfield. Falling lapilli described as the size of a football tore through metal and plexiglass. Among the airmen the injuries amounted to a sprained wrist and some cuts; the 23 people who died were civilians, killed by roofs collapsing under ash. Fact.
Around 672,000 people live in the Vesuvius red zone, across 25 municipalities, and the evacuation plan assumes they can be moved in 72 hours. Fact.
Nine famous facts that are not facts
This is the part worth reading, because every one of these is repeated confidently in guidebooks, on tours and across the internet.
The Krakatoa explosion measured 172 decibels. It could not have. The decibel was introduced in 1924 and named in 1929, forty-six years after the eruption. The figure is an arithmetical conversion of a single barometric reading, taken on an instrument at what the Royal Society report itself described as a non-scientific establishment. What is documented and needs no conversion: it was heard by people 4,800 kilometres away, and the pressure wave went round the globe three and a half times. Legend, as a measurement.
Krakatoa killed 36,000 people with its eruption. It killed them with water. Of 36,417 deaths, 34,417 were caused by the tsunamis, which is 94.5 per cent. The total is a fact; the attribution is usually wrong.
Tambora made Mary Shelley write Frankenstein. Two problems. The Shelleys were not staying at Villa Diodati, which was Byron's house; they were at Campagne Chapuis nearby. And the causal link to Tambora has an entire academic paper devoted to dismantling it. The wet summer was real. The chain of causation is a retelling. Legend.
Laki killed a fifth of Iceland's population. The 20 per cent is the population decline, not the death toll, and much of it is births that did not happen. Excess deaths were around 8,000, roughly one Icelander in six, which is still among the worst mortality events in European history. And they died mainly of fluorine poisoning rather than hunger: eight million tonnes of fluorine settled on the pastures and killed over 60 per cent of the country's grazing livestock. The correction matters; the horror does not diminish.
Laki caused the French Revolution. Dismantled in print by the historian who knows the French harvest records best, as an old Anglophone historiographical legend. French harvests were good through 1787. Legend.
Laki killed 23,000 people in England. A misreading of a raw monthly total. Estimates of excess deaths are around 11,500 plus 8,200, and even those are contested, with at least one study finding 1783 within one standard deviation of normal. Legend, as usually stated.
Ludger Sylbaris was the only survivor of Saint-Pierre. He did survive the destruction of the town in an underground cell and was found four days later, and he did later appear with the Barnum and Bailey circus, all of which is documented. But he was not the only one, and this was already known to be false in 1903. Legend.
The third survivor of Saint-Pierre, a girl who escaped by boat. Her account appeared in an instant book in 1902 and contradicts itself: she places the event at vespers when the eruption was in the morning, and describes lava that did not occur that day. Legend, and self-refuting.
Pele's curse. The belief that taking lava rock from Hawai'i brings misfortune was invented in 1946 by a park ranger who was tired of theft. Research into Hawaiian folklore is unambiguous: there is no traditional belief that Pele objects to rocks being moved. Legend.
And yet you still should not take the rock. The cultural objection to removing material is real, predates the invented curse, and does not depend on it. Removing rock from a United States national park is also illegal. Fact.
Two that are genuinely unresolved
The sky in Munch's The Scream is the Krakatoa sunset. A popular and attractive theory, challenged in recent years on two grounds: Munch's own writings describe a single specific evening, and volcanic haze does not explain the banded, rippling structure he painted. Some researchers now favour mother-of-pearl clouds. Disputed.
The 1707 Fuji eruption was triggered by an earthquake. It began exactly 49 days after a magnitude 8.6 earthquake and lasted sixteen days, which is suggestive. The physical mechanism is modelled and plausible and remains a hypothesis. Related correction: the ash measured at Edo was about two centimetres, not the five to ten that circulates. The deeper excavated deposits are ash that was swept into heaps during the clean-up. Disputed.
The ten misconceptions that matter for your safety
| What people believe | What is actually the case |
|---|---|
| If a volcano is active, there is lava to see | Active means supplied with magma and capable of erupting, not erupting now. Around 1,350 volcanoes are potentially active and a handful have visible lava at any moment |
| Dormant means safe | Activity sits on a graded spectrum with heavy overlap. Pinatubo was quiet for about five hundred years and then produced a VEI 6 that killed 847 people |
| An N95 mask protects me from volcanic gas | It helps against ash and does nothing against gas. Sulphur dioxide and hydrogen sulphide need an acid-gas cartridge respirator, and nothing filters carbon dioxide. For a visitor, the protection is distance |
| No eruption means no danger | Most visitor deaths happen without a magmatic eruption: steam explosions with no precursors, carbon dioxide on calm days, rain-triggered lahars, and lava bench collapses |
| Lava moves slower than I walk | Usually true, which is what makes it dangerous. At Nyiragongo silica-poor lava reached 60 km/h. Where the geology allows it, lava becomes a fast fluid |
| The aviation colour code and the alert level are the same scale | Two separate systems, assigned independently. One measures ash for pilots, the other ground hazard. An effusive eruption can be Warning on the ground and only Orange in the air |
| Volcanic ash is just dirty | It is pulverised rock and glass, abrasive and sharp. Millimetres close an airport; wet, it collapses roofs, which is the main cause of death in ash-fall eruptions |
| You can see blue lava at Ijen | There is no lava and no eruption. There is a sulphur vent. Blue is the colour sulphur burns, not the colour of molten rock, and it is invisible by day |
| If I can smell sulphur I am alert; if it stops, it has passed | Backwards. Hydrogen sulphide deadens the sense of smell as concentration rises. A sudden loss of the smell should be treated as deterioration: move uphill and upwind |
| The Ring of Fire holds 75 per cent of the world's volcanoes | Closer to two thirds by the standard catalogue. The solid and more striking figure is that it holds around 90 per cent of the world's earthquakes |
One last one, which is our favourite
The word volcano is a place name that became a common noun. It comes from Vulcano, one of the Aeolian Islands north of Sicily, which the Romans associated with Vulcanus, the god of fire, on the reasonable assumption that the smoking island was his workshop.
The same small archipelago gave the world a second technical term. Vulcanian, the eruption style, is named after the same island. And a third comes from just up the coast: solfatara, now used by geologists everywhere, is the name of a single crater at Pozzuoli near Naples.
Three words in the international scientific vocabulary, all from one stretch of the Tyrrhenian coast, all because that is where Europeans first got close enough to a volcano to need names for what they were seeing.
You can take a ferry to Vulcano from Milazzo in about an hour.
The island that named the phenomenon
Vulcano is one of the Aeolian Islands, an hour by hydrofoil from the Sicilian coast, and the reason the word exists at all.
The people who watch them
Japan counts 111 active volcanoes and watches 51 of them around the clock. The definition it uses is broad: anything that has erupted in the last ten thousand years, or that has vigorous fumaroles now. Fuji is on the watched list. Fact.
The world's airborne ash is divided between nine centres. They are in London, Toulouse, Anchorage, Washington, Montreal, Darwin, Tokyo, Wellington and Buenos Aires, and each is responsible for a slice of the planet. Italy and the Mediterranean, including Etna, are Toulouse's problem. Fact.
Pinatubo is the case that justifies the entire profession. It had been quiet for around five hundred years when it produced a VEI 6 in 1991, injecting some 17 million tonnes of sulphur dioxide and cooling the planet by about half a degree for two years. It killed 847 people. Roughly 60,000 had been evacuated first, on the strength of monitoring data. Fact.
The Decade Volcanoes are not the most dangerous ones. The list of sixteen, drawn up in the 1990s for a United Nations disaster-reduction decade, is routinely presented as a danger ranking. One of the actual selection criteria was that the volcano be politically and physically accessible to study. It is a research shortlist. Fact.
Ontake killed 63 hikers on a fine Saturday in 2014, with no significant precursory seismicity, because it was a steam explosion rather than a magmatic one. It is Japan's worst volcanic disaster since 1902, and it happened on a busy, well-known mountain in perfect autumn weather. Fact.
The Whakaari prosecutions did not all stick. After the 2019 eruption killed 22 of the 47 people on the island, New Zealand's regulator charged thirteen parties. On 28 February 2025 the High Court overturned the conviction of the company that owns the island. The case reshaped volcano access law well beyond New Zealand, and its final shape is still being argued. Fact.
Data verified on. Every item was checked against a primary source. Anything we could not verify was left out, and where specialists disagree we have labelled it disputed rather than picking a side. Editorial Policy