Lucia Civetta lives in something approaching heaven for a vulcanologist. A lecturer in geology and vulcanology at Naples University, she is also the director of the Vesuvius Observatory, which monitors volcanic activity deep in the viscera of the earth and carries out research into new methods of exploring and predicting the goings-on under the world-famous landmark overlooking the Bay of Naples.

"Vesuvius is probably the world's most dangerous volcano," explained Professor Civetta. "It is very much an active volcano, and has erupted violently many times in recent centuries. In 1631, 4,000 people were killed, in 1944 about 50 died and hundreds of homes were swept away by tides of molten lava."

Incredibly, 570,000 Neopolitans have built their homes on foothills which in the past have been swept by the lava. On the coastal rim of the Bay of Naples, southeast of the city, fishing villages like Pritici and Torre Del Greco have grown into vast, overcrowded, poverty-stricken and crime-ridden dormitory suburbs. It was here that hot lava slid sizzling into the sea.

In what an official of the Italian civil defence authorities described as "40 years of criminal negligence", thousands of cheaply built multi-storey blocks have been built on the slopes of Vesuvius. Regardless of unenforced planning regulations, they are crammed together without enough access roads to make a speedy evacuation possible.

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The Vesuvius Observatory is the front line of defence against a disaster which might take place tomorrow, next year or in 100 years. It is also the world's oldest volcanic monitoring centre, established in 1841 by Ferdinand II, the Bourbon King of Naples.

"Vesuvius erupted many times in the 18th and 19th centuries," said Professor Civetta. "In paintings from that period the volcano is always portrayed with a plume of dark smoke rising from its crater. It attracted visitors and scientists from all over the world. Since 1944 it has been fairly quiet, although seismic and magmatic activity continues. Today Vesuvius is one of the world's most interesting laboratories for geological and vulcanological research, and the only one in Europe."

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The original observatory is at a height of 600 metres on the volcano, which is itself 1,200 metres above sea level. Half of it is being restored as a museum of vulcanology, the rest houses the technicians who monitor Vesuvius's activity. A former religious retreat nearby has been turned into living quarters for students of vulcanology and geology from various universities. The main headquarters of the observatory, where the data obtained is studied and analysed, has been moved to Naples proper, about ten miles away.

In terms of the quality of research into the mysteries of volcanic phenomena, Professor Civetta claims that the Vesuvius Observatory is on a par with the major American and Japanese institutes. Yet its primary concern remains that of providing early warning for the next eruption.

"We have been telling the authorities of the danger for decades," says Professor Civetta, "And of course Vesuvius may have decided to keep quiet for many years. But there is really no way of telling when it will erupt again. The only thing we can say is that with the monitoring systems which we now have we should, and I say should, be able to give a couple of weeks' warning of an eruption. We must also bear in mind that Vesuvius is what we call an 'explosive' volcano, in that when it erupts it does so with explosive violence. Etna, in Sicily, for instance, begins to gradually flow with lava. But Vesuvius is different, it goes like a gigantic champagne cork."

A premature and false alarm would reduce the credibility of any subsequent warnings. An alarm too late might not provide enough time for the evacuation of 570,000 people from areas which have a population density comparable to that of Hong Kong.

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"As we start monitoring the first rumblings we will inform the interior ministry, and keep them informed as the situation develops. They will have to decide when and how to order an evacuation," says Professor Civetta.

The civil defence ministry already has a contingency plan ready to evacuate areas as they are threatened. The destinations of the evacuees, however, are being kept secret, possibly to avoid protests from areas fearful of having a few hundred thousand Neapolitan refugees to deal with.