As the letters attest, thousands of visitors have reconsidered their views on what they once regarded as local superstitions.

Larry Bell, owner of a large plumbing and heating company in Denver, considers himself a realist, not much given to New Age mumbo-jumbo. But he says trouble abounded after he picked up a marble-size piece of lava for a friend. In the six years since his trip to Hawaii Volcanoes National Park, Bell's daughter has been plagued with serious health problems, his marriage was strained to the breaking point, he has been forced to relocate his business and he unexpectedly needed heart surgery.