The drive-in takes you to a somewhat disappointing acre or two of boiling mud, steam and sulphurous gas - from which foul-smelling element all four West Indian Soufrieres derive their name - and the minibus hordes are guided through at such a breathless pace that the experience can be fitted in between a late breakfast and an early lunch. To those dismayed by the distinct lack of lava, the guide is unapologetic: "It's only thanks to us that all the other islands on the fault line don't go up," he boasts. "This is the safety valve on the pressure cooker, where all the gases can escape. Martinique, St Vincent and the others should really be paying us a volcano tax." The science may be doubtful, but the humour is very St Lucian - and he may just be right.
Every year, up to 200 vulcanologists keep a weather-eye on any subtle changes in Soufriere's activity that may portend future disasters on the scale of Montserrat, or, at the beginning of the century, Martinique, where all 30,000 inhabitants of the former capital, Saint-Pierre, were suffocated or burnt to death when Mount Pelee erupted.
And, for all its latter-day tameness, St Lucia's under-performing volcano has left behind two of the scenic icons of the West Indies: the dramatic Piton peaks, soaring sheer out of the sea almost to the clouds.
Not that St Lucia's 240 square miles of rainforest, banana plantations and contrasting coastlines are short of eye-catching vistas. The majority of visitors base themselves in the north-west strip of low-rise hotels that stop just short of disfiguring the beaches. One stretch of coastline near the capital, Castries, has been sacrificed to a massive American- owned oil-storage depot, while in the north, on the ribbon of empty sand between Rodney Bay and the 18th-century British naval look-out at Pigeon Island, a sprawling Hyatt Regency is being knocked noisily into shape amid the palms.
And yet, just a few miles away, the potholes in the island's major road are so deep and dangerous that locals have protested by placing banana plants in the middle of the carriageway - just in case the roads minister happens to be passing.
The gulf between rich and poor on St Lucia is as pronounced as anywhere in the developing world, but the fact that the island's beaches are all public means that the two extremes collide on a routine basis. The clients of even the most deluxe hotels are periodically roused from their beach- slumbers by hawkersplaying a game of cat-and-mouse with the beach police, trading illegally in anything from soothing skin balm (you need a vendor's licence) to drugs (banned outright).
The offer of an adroitly carved coconut bird-feeder or a necklace of semi-precious stones invariably leads on to the whispered "I can offer you the best ganja on the island, man". Alluring to some, of course, but sinister and threatening to others. The traders size you up and offer accordingly. One of them quick-wittedly abandoned his attempts to sell me drugs when he spied an elderly, rather sunburnt American lady approaching. "Take the sting out of your skin, ma'am!" he cried, producing an aloe vera plant from his satchel like a rabbit from a magician's hat. I marvelled at his salesmanship, but worried about the damage the black marketeers are doing, not only to the island's banana-dependent economy, but also to its image.
A few days in the sunshine, though, and the heavy selling cools. The torso starts to brown, anxieties recede, and a kind of beach-wise cool is developed. One teenage jewellery trader, fresh out of school, finally abandoned his sales patter and told us of his dreams: one day he wanted to operate a fleet of motorboats. But why didn't he look for a job at one of the new hotels? "There's no sense in working up there, man - they'd pay me 40ECs a day [Eastern Caribbean dollars: less than pounds 10] - and you can make as much selling a necklace to a tourist." It was hard to feel affronted after that.
We had stepped on to the island from the grey of Gatwick, anxious not to waste a few precious days in the sun simply sizzling on the beach. We booked a series of excursions - to the rainforest, to the mountains by jeep, a sunset cruise by tall ship, a historical tour of a colonial plantation. All very worthy and improving, but totally eclipsed by the simple, easy-living, mind-emptying magic of the Caribbean beach. We were almost instantly tranquillised.
The colours really are as vivid as the travel agents' posters suggest. Even the most tremulous swimmer is seduced from the shade of the palm across the sand and into the warm waves. The heat is tempered by the Caribbean's built-in air conditioner, the trade winds that blew Columbus there 500 years ago. And to accompany the sundowner, the distant sounds of reggae and calypso are counterpointed by a chorus of tree frogs, a pleasing reminder that you are a long way from home.
On the last day, we had almost to be dragged off the beach, resolving never to allow another winter to pass without returning to the Caribbean - although preferably a little less expensively in future. We had barely scratched the surface of the island, but it hardly seemed to matter. Nothing seemed to matter. And maybe that's the best thing St Lucia has to offer. We had touched that valve, and all the pressure had been released. Just as the wise man at Soufriere had promised.
Frank Partridge paid pounds 976 for 11 nights in St Lucia with Kuoni (01306 742222), including scheduled flights on British Airways from Gatwick and room-only accommodation at the three-star Rex St Lucian.
The 1999 St Lucia Jazz Festival takes place throughout the island between 8 and 16 May. For more details contact the St Lucia Tourist Board at 421a Finchley Road, London NW3 6HJ (0171-431 3675) or visit www. stluciajazz.com