BILLINGS -- Even by Yellowstone National Park standards, Giant Geyser is a show-stopper.

When it erupts, it shoots a roaring, splashing column of water and steam, often higher than its more predictable and famous cousin, Old Faithful.

Problem is, Giant is fickle, going months, even longer than a year, without erupting before suddenly coming back to life.

This is one of those times.

Over the last two years, the erratic geyser in the Upper Geyser Basin has been busy, erupting with a frequency not seen since the 1950s. It's been a kick for those lucky enough to see it.

"It's just thrilling an awful lot of people," said T. Scott Bryan, author of "The Geysers of Yellowstone," who has been tracking Giant's activity. "So many people have been able to see it for the first time."

In recent months, Giant has been erupting roughly every five to eight days. Surprised passersby have been treated to eruptions 200 feet or higher.

It's been perhaps the most talked-about feature among Yellowstone "geyser gazers" since it began its resurgence in August 2005.

"It's one of the special and rare ones to see," said Udo Freund, chief operations officer of the Geyser Observation and Study Association.

Giant has a long, storied history in the park.

It was named on the same day -- Sept. 18, 1870 -- as Old Faithful by members of the weary Washburn expedition who, just a day before, were in disagreement about exactly where they were and where they were headed.

That day, they watched an hour-long eruption of Giant spewing more water from its broken, 12-foot high cone than any other geyser they'd seen, according to historian Aubrey Haines' "The Yellowstone Story."

The cone looks like a "giant hollow tree stump with part of the side broken away to expose the six-foot aperture through which its waters are discharged," according to Haines' description.

"The Giant is a rugged deposit, presenting in form a miniature model of the colosseum," Nathaniel Langford, one of the members of the expedition, wrote in his diary.

For years, activity shifted back and forth between Giant and nearby Grotto geyser, apparently driven by an exchange of underground heat, water and energy. The early 1950s were one of the busiest times for Giant, erupting 137 times in one year.

The 1959 earthquake centered near Hebgen Lake changed the dynamic. Giant erupted infrequently -- sometimes going dormant for as long as 454 days -- picking up in 1997 and again in the summer of 2005.

Giant, near the Firehole River, erupted 46 times in 2006. So far this year, at least 49 eruptions have been noted, the most since the 1950s. Geyser enthusiasts have also gotten a few sneak peeks at Giant on an experimental live, streaming Web cam the Park Service has set up and hopes soon to debut officially.

Close watchers in recent years have been picking up on signs that Giant might be ready to erupt, but the geyser, like others in Yellowstone, always holds a few surprises.

"It's got its habits we're kind of learning to recognize," said Bryan who has seen 15 Giant eruptions in the last two years.

Katy Duffy, Yellowstone's west district interpretive ranger, said Giant has been a point of fascination for rangers and visitors to Old Faithful. As Giant awakens, there's often a stampede to the boardwalk to get a better view of eruptions that start out strong and can last up to an hour, followed by a steamy phase.

"It's awesome, it's huge, it's a great natural show," Duffy said

She saw a Giant eruption from the beginning in the summer of 2006. She had positioned herself for an unencumbered view, but also got soaked in the process.

"I was cold but it was worth it," she said.

So what to make of Giant's resurrection? No one's really sure. Most of the activity that drives Yellowstone geysers happens unseen in the complex, superheated plumbing system below ground.

"There's almost an infinite number of possibilities that could be causing the change in an individual geyser," said Henry Heasler, Yellowstone's lead geologist.

Yellowstone, if nothing else, is a place of constant change. Giant is lively now but there's no saying it won't suddenly fall again into quiescence.

"We're just enjoying it and hoping it continues," Duffy said.