Free Santorini by Alistair MacLean Page A

number means in the term the greatest good of the greatest number.

    'It is commonly enough imagined that earthquakes and volcanic eruptions are two faces of the same coin. This is not necessarily so. The venerable Oxford English Dictionary states that an earthquake is specifically a convulsion of the earth's surface caused by volcanic forces. The dictionary is specifically wrong: it should have used the word "rarely" instead. Earthquakes, especially the big ones, are caused when two tectonic plates  --  segments of the earth's crust that float freely on the molten magma beneath  --  come into contact with one another and one plate bangs into another or rubs alongside it or dives under it. The only two recorded and monitored giant earthquakes in history were of this type  --  in Ecuador in 1906 and Japan in 1933. Similarly, but on a lesser scale  --  although still very big  --  the Californian earthquakes of San Francisco and Owens Valley were due to crustal movement and not to volcanoes.

    'It is true that practically all the world's 500 -- 600 active volcanoes  --  someone may have bothered to count them, I haven't  --  are located along convergent plate boundaries. It is equally true that they are rarely associated with earthquakes. There have been three large volcanic eruptions along such boundaries in very recent years: Mt St Helens in the state of Washington, El Chichon in Mexico and one just north-west of Bogota in Columbia. The last one  --  it happened only last year  --  was particularly nasty. A 17,000-foot volcano called Nevada del. Ruiz, which seems to have been slumbering off and on for the past four hundred years, erupted and melted the snow and ice which covered most of its upper reaches, giving rise to an estimated seventy-five million cubic yards' mudslide. The town of Armero stood in its way. 25,000 people died there. The point is that none of those was accompanied by an earthquake. Even volcanoes in areas where there are no established tectonic frontiers are guiltless in this respect: Vesuvius, despite the fact that it buried Pompeii and Herculaneum, Stromboli, Mt Etna and the twin volcanoes of the island of Hawaii have not produced, and do not produce, earthquakes.

    'But the really bad apples in the seismic barrel, and a very sinister lot those are, too, are the so-called thermal hotspots, plumes or upswellings of molten lava that reach up to or through the earth's crust, giving rise to volcanoes or earthquakes or both. We talk a lot about those thermal plumes but we really don't know much about them. We don't know whether they're localized or whether they spread out and lubricate the movements of the tectonic plates. What we do know is that they can have extremely unpleasant effects. One of those was responsible for the biggest earthquake of this century.'

    'You have me confused, Professor,' Hawkins said. 'You've just mentioned the really big ones, the ones in Japan and Ecuador. Ah! But those were monitored and recorded. This one wasn't?'

    'Certainly it was. But countries like Russia and China are rather coy about releasing such details. They have the weird notion that natural disasters reflect upon their political systems.'

    'Is it in order to ask how you know?'

    'Of course. Governments may elect not to talk to governments but we scientists are an incurably gabby lot. This quake happened in Tangshan province in north-east China and is the only one ever known to have occurred in a really densely populated area, in this case involving the major cities of Peking and Tientsin. The primary cause was undoubtedly a thermal plume. There are no known tectonic plate boundaries in the area but a very ancient boundary may be lurking in the area. The date was July 27, 1976.'

    'Yesterday,' Hawkins said. 'Just yesterday. Casualties?'

    'Two-thirds of a million dead, three-quarters of a million injured. Give or take a hundred thousand in each case. If that sounds flippant or heartless, it's not