Coming down from the University of Washington, where he a graduate student in geophysics, Ronnholm put aside his studies of Martian atmosphere to take in a relaxing weekend at Mount St. Helens. It was Saturday, May 17th. The mountain had been spewing small amounts of ash and steam and rumbling with earthquakes for nearly two months. Scientists said the bulging north slope was sitting on marbles, but to far no major eruption had occurred.

If he got lucky, Ronnholm thought, he might get a dusting of ash at his campsite in Bear Meadow 10 miles to the northeast.

What he got was something far more valuable: A sequence of photos of Mount St. Helens that later helped scientists reconstruct just how the mountain collapsed and exploded that day, and which made Ronnholm something of a celebrity in the world of volcano watchers.

As he headed out that Saturday, however, there was no inkling that Ronnholm was about to record history.

"There was no anticipation it was going to be a big deal," Ronnholm, 53, of Seattle recalled recently. "Even among conversations in the UW Geophysics Department there wasn't a conversation where somebody said 'It's really going to blow.' "

Not much happened that Saturday, Ronnholm said. He camped out in the back of his truck, enjoyed a beer and a science fiction novel and chatted with a couple of other sightseers at the picnic area.

Even if nothing much happened, Ronnholm said, the trip would be successful if he could see even a small eruption.

"I could say I've seen a volcano erupt," he said.

At 8 a.m. Sunday he still relaxing in bed and reading his novel. He first ignored the shouting from other campers, thinking it was a parent yelling at their kids. "Then it dawned on me that I was near a volcano," he said.

Looking up, Ronnholm saw a lot more than what he'd come for.

"The entire north face of the mountain, what was called the 'bulge,' was sliding down," he said.

At first forgetting he'd come to take photos, Ronnholm hesitated getting his camera. "I thought, 'I'll never get it focused in time, this is all happening too fast,' " he said.

Standing third ridge removed from the mountain, Ronnholm thought he had a good spot to view the geologic event of a lifetime. He began snapping pictures with his 35mm Minolta as a lateral blast shot out of the volcano and swirled and boiled toward him

Ronnholm said he was not worried.

"There's no way you think that is going to come to you," he said. "It's not part of our human experience that things 10 miles away are going to hurt us."

As the cloud of ash rose 15 miles into the sky and mushroomed overhead, Ronnholm watched it come galloping over the second ridge. He started to get worried.

"It curled and broke over that ridge, and that ridge didn't stop it," he said, noting that he began to think, "Maybe I should find my pants and get my car keys."

Ronnholm spent half a minute getting himself together, while still keeping an eye on what was unfolding before him.

"I was all the while trying to watch it, because it's a fascinating thing to watch. You don't want to miss anything."

The sound of the blast might have spurred a flight response, he said, but there was none due to an oddity in the way the sound traveled.

"It's all happening off in the distance," he said. "It doesn't feel the least bit scary, it's fascinating."

The cloud was coming towards him "dramatically fast" when he looked around and noticed the Bear Meadow parking area was almost deserted.

"As I watched it grew in my vision, it's coming towards me and I realized it was time to leave," he said. And quickly.

"The last picture that I took was over my shoulder, it seems like it is almost on me," he said.

Ronnholm went racing down a logging road, following everyone else ahead if him out of Bear Meadow.

Feeling that he was going to be swallowed up by the approaching blast, Ronnholm found the real risk was rock blasted out of the mountain and falling in a rain about him. Golf ball-sized rocks were leaving craters in the road, and bouncing off the hood and windshield. Soon, they were replaced by drops of mud, sticking to the car, and then a torrent of ash.

Enveloped in a cloud of ash so thick they couldn't see, a chain of cars crawled out of the forest. Out in front of the lead car, two men on foot each kept one hand on the bumper while they felt with their feet for the road in front of them.

"If the first vehicle had gone off the road and off a cliff, I'm sure we all would have," he said.

Eventually Ronnholm and his fellow refugees crept out of the forest and made their way to Morton.

Ronnholm's pictures have been published repeatedly in the years since, on the cover of Nature magazine and regularly in scientific journals, textbooks and documentaries in the years since. He's made some money from sales of the photos, but not very much, he said.

"I'm not retired and living off the proceeds by any means," he said.

More important to Ronnholm is what volcanologists have been able to learn from they way Mount St. Helens erupted, and his contribution to that.

"Flank collapse in volcanos is much more common than previously believed," he said.

Scientists now understand that towns and villages within 20 miles of active volcanos that may be in more danger that they knew.

"That wasn't an appreciated aspect of what Mount St. Helens could do," he said. "Most people were talking about plumes of ash."