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Daily Dose / Nov 7, 2026 / Volcanoes
One in Six This Century
The last truly enormous eruption was Tambora in 1815, which brought Europe and North America a "year without a summer." Volcanologists put the odds of another one before 2100 at roughly a roll of a die, and say we are barely preparing for it.
1 in 6
Chance of a magnitude-7 eruption this centuryThat is a Tambora-class blast, 10 to 100 times bigger than Hunga Tonga in 2022. Ice cores suggest one comes about every 625 years, twice as often as previously thought.Cassidy & Mani, Nature, 2022
01 · The scale
Each step is ten times the last
The Volcanic Explosivity Index ranks eruptions by how much material they throw out. Every step up means roughly ten times the volume.
VEI scale: Newhall & Self (1982), via USGS / Smithsonian Global Volcanism Program. Example placements are standard published classifications.
02 · The odds
Small each year, large over a lifetime
At about one magnitude-7 eruption every 625 years, the yearly risk is tiny. Add up a century and it becomes a real possibility.
625
years · average gap between magnitude-7 eruptions
Cassidy and Mani's figure comes from ice-core sulfate records of past eruptions. A steady 1-in-625 yearly rate gives about 15% over a century. They round the century risk to "1 in 6."
Of the 97 large-magnitude eruptions logged in the last 60,000 years, scientists know where only a handful happened.
Modeled curve
Curve = 1 − e−t/625, an illustrative Poisson model built from the published return interval. It is not a forecast for any specific volcano.
03 · The reach
Tonga punched into the mesosphere
In January 2022, Hunga Tonga's plume reached 57 km, the tallest ever recorded by satellite and five times higher than airliners fly.
Plume heights: Proud, Prata & Schmauß, Science (2022). Airliner cruise altitude is a typical reference value (~10–12 km).
04 · The climate
A single eruption can change the sky
Big eruptions load the stratosphere. Sulfur cools the planet, while water vapor traps heat. Tonga did something no satellite had seen before.
Stratospheric water, before vs. after Tonga
Existing stratospheric water = 100+~10 (146 Tg)
NASA's Aura satellite measured 146 ± 5 million tonnes of water injected into the stratosphere, about 10% of the water already there and far beyond anything else in the satellite era.
~20 Mt
sulfur dioxide from Pinatubo, 1991
That sulfate haze cooled parts of the globe by as much as 0.5 °C. Tambora, a magnitude 7, threw out about three times more sulfur and was followed by 1816's "year without a summer."
Millán et al., Geophysical Research Letters (2022); USGS, "Do volcanoes affect weather?" (Pinatubo ≈ 20 Mt SO₂, cooling up to ~0.5 °C).
05 · The stakes
A small eruption already cost billions
Eyjafjallajökull was only a VEI 4, but its ash shut down European airspace. A magnitude 7 ejects roughly a thousand times more material and hit a far more connected world.
800M
people live within 100 km of an active volcano, across 86 countries
Brown et al., 2015
100,000
flights cancelled in 2010, with ~10M passenger journeys disrupted and $1.7B in lost airline revenue
EUROCONTROL · IATA, 2010
Trillions
of dollars in losses expected from a magnitude-7 eruption, comparable to the pandemic
Cassidy & Mani, 2022 · expert estimate
Why it matters · what you can do
Prepare for the volcano we can't name yet
Know your exposure. If you live near a volcano, look up its hazard map and evacuation routes. Many countries publish them through their geological survey.
Back monitoring. Many active volcanoes still have no ground sensors. Observatories run on modest public budgets that are easy to cut.
Plan for disruption, not just destruction. Ash can halt flights, crops and supply chains thousands of km away. Have travel and supply buffers.
Ask for global planning. Cassidy & Mani note that spending on asteroid defense far exceeds spending on preparing for large eruptions, even though eruptions are far more likely.