"Volcanoes have such awesome power," effuses volcanologist and explorer John Seach. "And yet they are not just destructive. They're beautiful, too. And, over time, they leave behind such beauty. There is absolutely nothing in the world like a volcanic eruption."

While eulogizing over his favorite topic, Seach is scrambling ahead of me, over treacherously sharp rock at the base of Kilauea, an erupting Hawaiian volcano and one of the world's most active. Above us, molten lava is flowing down the mountainside.

"Oh, mate; what a beauty. It's fantastic. But bloody hell, it's hot," he announces excitedly, gazing at the lava flow and sounding for all the world like the late "crocodile hunter" Steve Irwin, taunting a giant saltwater croc. While we're making comparisons, he bears a strong resemblance to Russell Crowe, too: all square-jawed, squat and muscular, but without the attitude. Same accent, too. Somehow it seems wholly appropriate that a maverick scientist, famous for his daredevil rappelling down live volcano craters to observe lakes of hot lava, should be Australian.

Born in Sydney, Seach now lives on a sugar cane farm in New South Wales. In the late 1980s, following a chemistry degree from Sydney University, he worked as a scuba diving instructor in the Solomon Islands in the Pacific, where he regularly observed the live volcano Tinakula. "It is a perfect cone, emerging from the ocean," he says. "One of the most beautiful volcanoes in the world. I used to sit on the beach and watch it erupting. I was fascinated by its awesome power and majesty. I wanted to learn more, but it was difficult as almost nothing had been written about it. That's true of most of the world's volcanoes. Some—such as Kilauea and Mount Etna in Sicily—are well observed by volcanologists. But the vast majority go unnoticed." Seach's initial observations on Tinakula went on to be published by the Smithsonian Institution.

Fast-forward 15 years and John Seach is now one of the world's leading volcanologists and explorers, as well as one of its best known. Two Discovery Channel documentaries have been devoted to his work and, more particularly, his habit of rappelling down craters to see the steaming cauldrons of lava up close.

There are more than 1,500 active volcanoes in the world, in locations as diverse as Antarctica, mainland USA, Russia, Iceland, the Congo and the central Pacific Ocean. Every year, there are about 50 eruptions—Seach's goal is to visit as many as possible and observe them.

"I go to see four eruptions a year," he says. "It doesn't sound like that much, but I think I visit more live volcanoes than anyone else."

The southwest Pacific is Seach's specialty, particularly the chain of volcanic islands that make up the small nation of Vanuatu. This is where he does most of his rappelling and makes many of his observations.

To observe and photograph, Seach likes to get as close as possible to the action. This is where he fuses his two passions: adventure and science. "I do take calculated risks," he admits. "Getting into a live volcano is dangerous. But rappelling into a crater is the best way to observe the lava lake or fire pit, and sometimes it's the only way to do so. Obviously, you have to be careful. It involves hiking up to the crater on a remote mountain, usually on a remote island, carrying heavy equipment. It involves camping in a tent for two weeks, sometimes in heavy rain as the weather can be weird and unpredictable around volcanoes."

Since the gases inside the crater are poisonous, Seach uses a respirator. This filters particles but does little else to protect him from the sulphuric mist he rappels into—a cocktail of steam, ash and noxious gases. If this sounds dangerous, it is. "There is an immediate risk of being poisoned or of choking," he admits. "Also, the rappelling rope is only good for one descent. The heat (the lava pit can be over 1,000 C and the air temperature in the crater will be at least 55 C) will ruin the rope, and so will the acidity of the environment. I tend to leave the rope afterwards, for the locals." He laughs. "Next time you come back, you often notice it's being used as a washing line."