SAN FRANCISCO -- Volcano chaser Robert Wenkam has some expert advice for trekking across hot lava -- move fast.

"I've learned you can walk on a new lava flow within 30 minutes because it cools very quickly," says Wenkam. "Running is better than walking, though, because the feet can get very hot."

An adventurous photographer, Wenkam is an expert on nature's upheavals, having once chronicled the rare birth of a volcanic eruption on the island of Hawaii while the earth shook, cracked and smoked all around him.

For those who have never viewed a volcanic plume, walked in the rubble of a strong earthquake or witnessed the cracks, vents and ridges formed by active geological events, Wenkam transforms such experiences into a dramatic perspective in his richly illustrated book "The Edge of Fire" (Sierra Club Books, $35).

The continuing seismic and volcanic activity produced by the clash of two enormous land masses along the west coast of Central and North America have provided what Wenkam calls a "beauty and the beast" landscape of scenic wonder and ominous destruction that excites his photographic senses.

"There's nothing as dramatic as an erupting volcano," says Wenkam. "They're loud and noisy and the roar is continuous; it never stops. When the volcano is in a fountain, and I've seen them higher than the Empire State Building, you can be within a half mile and the heat is so intense you can't stay there.

"It's also the most beautiful thing you can imagine, with the changes of colors in the sky going through the entire spectrum. It's awesome and overpowering. It's something that cannot be described and that's no exaggeration."

Wenkam says his closest brush with disaster was when he photographed the birth of a new volcano on the east rift of Kilauea on the island of Hawaii by sneaking past the roadblocks and avoiding the authorities.

At one point, the sulfurous, toxic gases enveloped him. He finally reached an upwind area in time to revive himself. The incident, however, didn't discourage him from remaining in the area and capturing on film the destruction of the town of Kapoho.

"I try to be prepared to run," says Wenkam, who always takes a hard hat, heavy hiking boots and a knapsack with extra cameras to active volcanic sites. "I find it thrilling and exciting, an adventure and a challenge, but you have to be alert to the dangers."

Wenkam also has photographed the geology of California's High Sierras, shot scenes of the aftermath of Mount St. Helens' volcanic eruptions in Washington state, taken action pictures of Amatitlan Volcano in Guatemala and snapped the snow-capped beauty of the Iztaccihuatl and Popocatepetl volcanoes near Mexico City.

To document earthquake activity, Wenkam has photographed California's largest crack -- the San Andreas Fault -- and has documented the buckling of roads and the cracks in buildings from the medium-sized quakes that rumble periodically through the Golden State.

He notes that Los Angeles, located astride the Pacific oceanic plate, is moving toward San Francisco, part of the Continental plate, at a rate of four inches a year, that the Pacific Ocean grows wider by half an inch annually and that the Sierras, Tetons and Rockies are being squeezed and deformed by these movements.

Experts agree, Wenkam says, that a giant earthquake will deliver a knockout blow to Los Angeles within the next 14 years, most likely without warning. A large shock could also occur in Northern California, with catastrophic consequences to people living in homes built on landfill along the crowded peninsula.

All of the Cascades volcanoes, he says, are considered dormant but active, including Mount Rainier, Mount Hood, Mount Shasta and even Crater Lake. The Mammoth Lakes Resort in California's Mono County, he says, has molten magma bubbling in a caldera only 3,500 feet beneath the surface, which could erupt.

"We're dealing with something thrilling, beautiful and exciting and at the same time very deadly," says Wenkam, who was once saved from plunging into a collapsing lava tube by his large backpack. "It's a beauty-and-the-beast situation. What you love can turn against you and become dangerous at any second.

"We make national parks out of the beautiful landscape that the drifting continents have created. We admire all this beauty and at the same time we fear it.

"I find it all quite fascinating. We live on an earth that is moving and shifting and very much alive. We might as well enjoy it."

Wenkam says he's also photographed some of the other 392 volcanoes located along the Pacific plate's gigantic "ring of fire" and is ready, willing and able to start traveling for another book to complete the project. He's already photographed all of the Hawaiian Islands, which is why, he says, he's now residing in Irvine, Calif.

"The main reason I'm here is because I'm working on books and I ran out of islands," says Wenkam. "Otherwise, I'd still be living in Hawaii."

However, Wenkam doesn't consider his address to be permanent.

"Where I'm taking pictures is where I'm really living and that could be anywhere," said Wenkam. When he applied for a driver's license, he says, the state of California told him "the Earth" was not a specific enough location.