Every year, more than four million people walk across the top of one of the largest volcanoes on Earth. Yellowstone's last great eruption blasted out about a thousand cubic kilometres of rock and ash, a thousand times more than Mount St. Helens. So what would really happen if it erupted today? Hour by hour, day by day: what it would do to America and the world, and how close we really are to finding out.

The hidden caldera and the hotspot track across Idaho, the three great eruptions of the last two million years, the warning signs scientists expect, the eruption column and pyroclastic flows, the USGS ash model for the whole continent, the weight of wet ash, Tambora and the Year Without a Summer, Toba and the people who lived through it, the "overdue" myth, how much of the magma is really molten, NASA's idea to cool the volcano, and what Yellowstone is most likely to do next.

CHAPTERS
0:00 A park on top of a volcano
0:59 The volcano you can't see
2:34 Hour 0: the eruption
3:51 Day 1: the ash cloud
5:01 Week 1: roofs, power and food
6:15 Year 1: the summer that never came
7:26 Would humanity survive?
8:19 Is Yellowstone overdue?
9:52 Can we stop it?
10:38 Living on top of a volcano

A NOTE ON THE FACTS
The eruption in this video is the worst case, not a forecast. Ash thicknesses come from one modelled scenario (USGS Ash3d, Mastin, Van Eaton & Lowenstern 2014); climate effects of a supereruption are model estimates with wide uncertainty. The USGS considers a lava flow or a hydrothermal explosion far more likely than a supereruption, and the volcano's alert level is normal.

SOURCES
• USGS Yellowstone Volcano Observatory: eruption history, hazards, monitoring and FAQ
• Mastin, Van Eaton & Lowenstern (2014), Modeling ash fall distribution from a Yellowstone supereruption, Geochemistry, Geophysics, Geosystems
• Huang et al. (2015) and Maguire et al. (2022), Science: the Yellowstone magma reservoir
• Smith et al. (2018), Nature: humans thrived in South Africa through the Toba eruption
• NASA on Pinatubo's cooling; Eurocontrol on the 2010 Eyjafjallajökull airspace closures; USDA on world corn production
• B. Wilcox, NASA JPL (2015), study on cooling the Yellowstone hotspot

ABOUT THE VISUALS
Photographs are public domain (NPS, USGS, NASA, NOAA) or free-licensed (Wikimedia Commons). Maps use NASA GIBS shaded relief. Graphics are our own, built from the sources above. No AI-generated images are used. Narration, music and sound effects were created with ElevenLabs.

IMAGES (Wikimedia Commons, commons.wikimedia.org)
• Carsten Steger (CC BY-SA 4.0)
• Dietmar Rabich (CC BY-SA 4.0)
• European Space Agency (CC BY-SA 3.0 igo)
• Giorgiogp2 (CC BY-SA 3.0)
• yudhapohan (CC BY-SA 4.0)
• Andrew Hall (CC BY-SA 3.0)
• ThinkGeoEnergy (CC BY 2.0)

Stock footage: Pexels.

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