Volcanoes are all the rage in Tinseltown. Tim Cornwell looks at how the studios have attempted to cloak their hokum with a veneer of academic respectability.

The film Volcano opened in Los Angeles this week. The deliciously simple premise is of a volcano erupting under the city, sending molten lava rippling along Wilshire Boulevard and down the subways. With the motto "the coast is toast", and a current genre that treats the destruction of a major city as a visual joke - as in Independence Day - it seems bound to succeed. If that were not enough, it stars Tommy Lee Jones as a disaster coordinator, opposite a beautiful female geologist.

Los Angeles may be sitting on an earthquake fault, but there has been no volcanic activity for about ten million years. But when the producers of Volcano began to plot the film, they cast about for a spare vulcanologist to lend a veneer of authenticity. There is nothing film-makers like better than a heavyweight expert to help with "research". The question is, how does a self-respecting academic respond when approached with this kind of Hollywood nonsense?

The people at Fox 2,000 first contacted Jack Lockwood, a noted vulcanologist and member of the faculty of the University of Hawaii. Lockwood is far from averse to publicity - he runs a volcanic hazards appraisal business, and maintains a page on the world wide web, But he turned them down. "I have serious work to do, and this was not a serious film," he said.

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He did recommend a friend, Rick Hazlett, a professor of geology at Pomona College, part of the well-regarded Claremont cluster of colleges in California. Hazlett met the director and was, he says, "immediately thrown into the thick of it".

The film would make him cringe more than once, but he thoroughly enjoyed his brush with the film world. And he was able to entertain his geology class with the inside gossip from a set where whole boulevards were reconstructed, and then burned to cinders.

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Hazlett was experienced at screening volcanoes. In 1991, he was the lead scholar on a 26-part telecourse on volcanoes produced by the US public television service. He had also put together a 50-minute film showing the flow of lava into the sea at Hawaii. For the big screen, what he suggested as a model were some smaller eruptions that had occurred in the past 100,000 years in the Mohave desert, about 200 kilometres north of the city. "We took those eruptions and put them in Los Angeles," he said. "The writers wanted to know what we could expect, seeing what would happen in the big city." Paired with a civil defence expert, he could tell people what to expect from nature, and his colleague could tell people what to expect from government.

What followed was what Hazlett tactfully called some "picking and choosing" on the part of the film company. At first it bothered him. He remembers, in particular, long conversations with the writers about lava bombs, what they were and what they look like.

A lava bomb is a glob of hot lava shot through the air; as Hazlett remembered them from eruptions at places like Stromboli, in the Mediterranean, they are usually no more than a few feet across, trailing smoke. They are not glowing fireballs that explode on impact. But this is how they come off in the film, like napalm or "Greek fire being heaved at Byzantine warships," he said.

Then there was the whole premise that the eruption would begin in the La Brea tar pits. The tar pits are a celebrated site in the centre of Los Angeles, with a museum, where tar bubbles from the ground, due to the emission of crude oil from a fault. The geologist in Hazlett winced at the scenario that in place of oil, molten rock began to bubble from the ground. There are cities in the world - Honolulu and Auckland - where an eruption is more than conceivable. Not Los Angeles, certainly not for the next several million years.

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On visits to the set, much of Hazlett's work was taken up talking to visiting journalists, as part of the studio publicity machine. But he was a bit bemused by the ash, spat out by a machine and consisting of coarse pieces of newspaper painted grey. "I've been in an ash fall on several occasions, and the material is so fine, so powdery, that you can taste it before you see it." There was no other way to have material falling out of the sky that people could see, he said. "I had to get used to Hollywood magic." The ash machine used in Volcano was the same one used in Dante's Peak, another volcano drama released in Britain recently. Dante's Peak's consultant was Lockwood - hired after he had turned up his vulcanologist's nose at Volcano.

Dante's Peak, insists Lockwood, was a serious attempt to reproduce a possible eruption among the active volcanoes of the Cascades range on the Pacific coast, which include Mount St Helens. Vulcanologists - led by Pierce Brosnan - go on site, as they would in reality, to monitor for an impending eruption. The film was accurate enough to warrant a serious review in the magazine Nature, he said. "Every vulcanologist I know was on the edge of their seats."

"Education is the most essential strategy one has for volcanic hazards mitigation," said Lockwood. He cited the eruption of Ruiz volcano on Armero, where more than 24,000 people died. If they had heeded a six-hour warning, and left for higher ground, he said, casualties would have been minimal. "People have to be educated. I realised that this film, if it were done right, had educational potential. This is a chance to save lives and I am not saying that facetiously."

True, Dante's Peak includes a scene where a car drives across a lava flow, its wheels spinning in the molten rock for an agonisingly long period of time. But the producers, under advice, rewrote a scene in which Brosnan is publicly upbraided by his boss - something professional vulcanologists would never do, Mr Lockwood said.

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As an entertainment, Hazlett concluded, Volcano succeeds. It was not designed to educate people on volcanoes, and reflects that fact. But rather than "rattle the cage", he buried his own doubts, he said, when he remembered being inspired, as a young child, by the wholly unrealistic volcano scenes in Walt Disney's Fantasia.

Musing over titles for the next great Hollywood disaster film, he is thinking Global Warming. Meteorologists, beware.

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