Hurricane-like winds are another danger. "You sometimes get 100-mph winds curling up from the fire pit. You have to hang on and make sure you're well secured, with the pickets firmly hammered into the volcanic ash. Once down in the crater, though, it is usually very still.

"It is intensely hot and extremely hard work. It's like being inside a vast furnace. Yet, you have to wear full-length trousers and a protective, thick jacket in case you slip. If you fall, the newly dried lava will cut you to pieces. It is incredibly sharp; it's like falling on broken glass. That's why I would never just wear shorts and a T-shirt.

"In Ambrym, Vanuatu, I usually rappel for about 200 metres into the crater, which takes about 45 minutes to one hour. It is slow, careful and really tiring work. The final part of the journey to the lava lake is free climbing. I try to get as close as possible, to within 40 or 50 metres or so of the lava lake. But it is incredibly hot. You can't stay down there too long, maybe an hour or two. It's not just the heat; it's the fumes, too. It's an extraordinary feeling, almost indescribable, staring into a pit of molten lava directly connected to the inside of the earth. You can hear the earth rumbling and almost talking to you; hear the cracking and spitting; feel the heat; feel the earth moving. It is one of the most exciting and exhilarating feelings in the world."

That may be, but isn't it rather dangerous, too? Seach recalls that once, observing an erupting Mount Etna, he was hit by a piece of flying molten rock. "It hit me on the back," he says. "But it didn't hurt much, which surprised me. But, anyway, most volcanologists die in their beds." Later, he admits that most volcanologists study eruptions through sophisticated instruments, often safe in laboratories. They certainly don't rappel down to the action. But, conversely, neither does Seach do much scientific measuring. "I document and photograph what's really happening. Others theorize."

To observe Kilauea, Seach is wearing his usual rappelling, volcano-spotting garb: bright reflective orange jacket, jeans, hefty ankle boots, workman's gloves and plastic helmet. Sometimes he wears an astronaut-like, heat-reflective suit, which allows him to get even closer to the lava lakes, but which he claims is "bulky and difficult to rappel in."

Generally though, he isn't into expensive equipment. John Seach is one of the most down-to-earth, unassuming men you're likely to meet. "I'm enjoying staying in a hotel this time," he grins. "But the moment you go, I'll move into a cheaper log cabin. Mind you, even that is more luxurious than I'm used to. Normally, mate, I'd be camping in my tent.

"I want to get as close to the action as possible. I'd rather sleep right near the crater, or lava flow, than stay miles away and miss the action."

Kilauea is the youngest of the volcanoes on Hawaii's Big Island and, as befits a youngster, it is the most active. As we watch the lava spewing out of the crater and down the mountainside, Seach scampers around its battle frontline. It is slow moving—just 200 metres or so a day now—so that its path of destruction is easy to avoid.

The orange molten rock—hissing, crackling and bubbling, blowing pungent sulphurous fumes—smothers and burns everything in its path. Just occasionally, this tide of rocky fire—gravy-thick but four times as hot as an oven—hits a dip or a ravine and fingers of lava accelerate. Heat shimmers from its surface. Everything in its flow is obliterated: grass, trees, buildings. It is indiscriminate. Volcanoes are the most powerful force on earth: The eruption that destroyed Krakatoa in 1883 was 10,000 times more powerful than the bomb that was dropped on Hiroshima.

Only when the lava hits the sea, which it inevitably does on a small island, is it challenged. The lava attempts to assault the ocean, in a raw display of elemental fury: Earth, water and fire all combine in an explosive cocktail of heat and steam and brutal, crashing waves.

But even then the lava is not beaten. Over time, it accumulates.