Yellowstone: a geyser landscape on a supervolcano – scientists play out the worst case

Yellowstone National Park in north-western Wyoming is famous for geysers such as Old Faithful and its steaming springs. The cause lies deep underground: the Yellowstone Caldera, often called a "supervolcano", measures about 55 by 72 kilometres and sits above a mantle hotspot, similar to Hawaii. Over the past two million years it has produced three extremely large explosive eruptions, up to 2,500 times the size of the 1980 Mount St. Helens eruption. Today, its activity shows mainly in geothermal vents.

What a new super-eruption would mean was played out by scientists Ilan Kelman and Matthew Blackett in a thought experiment for The Conversation, republished by ScienceDaily. The last super-eruption, they write, happened about 631,000 years ago. In their scenario, an eruption column would rise 30 to 50 kilometres, far above the cruising altitude of commercial aircraft of up to about 13 kilometres. An evacuation zone would extend 100 kilometres beyond the park and affect about 200,000 residents.

In one of the models, up to about 1.8 metres of ash could fall on Billings, Montana, and up to about 1,000 people would die immediately, according to the scenario. Global cooling would probably not exceed about 1.5 degrees on the global average, the authors estimate. Importantly, this is a thought experiment, not a forecast. For visitors, the power beneath the surface still shows itself mainly in geysers and hot springs.