There's a scene in the hit disaster epic 2012 when John Cusack outruns a monstrous dust cloud from a volcanic explosion at Yellowstone National Park, as red-hot lava spews thousands of feet into the air and fireballs annihilate the surrounding landscape.

Cusack outrunning a dust cloud that size is a fantasy. The Yellowstone super volcano is not.

Much of Yellowstone National Park, which straddles the states of Wyoming, Idaho and Montana, sits on one of the largest volcanoes on the planet, and when (not if) it erupts, it'll be messy.

About 15 kilometres below the park, in a magma chamber 85 kilometres wide, a restless molten blob is bubbling and oozing like neon taffy. The pressurized heat and gases from this chamber are what cause Old Faithful and its more erratic brethren to spout.

The volcano has erupted three times in the last 2.1 million years, forming the series of calderas (underground chambers) illustrated here. The last eruption, 640,000 years ago, blasted a pillar of ash 100,000 feet in the air, leaving a hole in the ground larger than the Greater Toronto area. It devastated everything within a 50-kilometre radius. The plume spread layers of dust across North America as far as the Gulf of Mexico.

Meanwhile, a haze of sulphur dioxide mixed with water vapours was propelled into the earth's atmosphere, blotting out the sun. A period of global cooling cancelled summer – and whatever primitive barbecues may have been planned – for at least a year, maybe more.

The volcano is still very active, rising and falling under pressure at a noticeable rate for the last quarter century. The Yellowstone plateau has risen seven centimetres a year for the last three years, bulging like the belly of some gassy, lethargic monster.

Scientists agree: this volcano will one day blow its top.

Will yellowstone erupt within our lifetimes? Despite current seismic hyperactivity and occasional news reports spelling out a volcano-provoked apocalypse, experts say there's nothing to worry about.

"We don't think that anything going on right now indicates an eruption is coming anytime soon," says Jake Lowenstern, scientist-in-chief at the Yellowstone Volcano Observatory, one of five in the U.S. which monitor volcanoes for scientific purposes and public safety.

No one has ever seen an eruption as big as Yellowstone's could be. All suppositions are based on blasts a tenth of the size, that history has recorded.

"It's of dubious information content of what would or would not happen because we don't ultimately know," Lowenstern says.

The Yellowstone observatory was founded in 2001 to monitor the volcano's erratic behaviour with seismographs and other devices plugged deep into the earth, with antennas poking from the surface like metal flowers. They feed information to researchers across the U.S. via satellite.

While an eruption is unlikely to come soon, earthquakes happen all the time.

In 1959, a 7.5 magnitude quake adjacent to the park killed 28 people. Last Christmas, hundreds of small quakes kept geologists on their toes — they were the most energetic earthquake "swarms" to occur in the park in decades.

It's no 2012 fantasy that the Earth could hiccup and shudder at any moment, and before we know it mountains could be levelled or cities buried in ash. Scientists say they could predict an eruption by days or even months; an earthquake by not so much.

"Nobody ever knows with absolute certainty anything in science," Lowenstern says. "We are quite good at forecasting eruptions around the world, but it's a little trickier at a place like Yellowstone because it's very active."

Being warned may not matter.

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Even a "small" Yellowstone eruption would be well beyond our current acquaintance with what volcanoes are capable of.

The worst might not come first. Toronto would see a sprinkling of dust and possibly a few weeks of spectacular sunsets. Then, with the rest of the planet, we'd feel the climatic effects – forests and wildlife under stress, disruption of agriculture for years. Summers would be cancelled, barbecues and all.

The Earth won't end. But humanity . . . well, the films can speculate on that.