Dozens of massive explosions within Mt. St. Helens sent mushroom-shaped clouds of steam, gas and volcanic debris soaring more than 20,000 feet above the Pacific Northwest today, while mudslides and avalanches rumbled down the sides of the almost 10,000-foot peak.

Despite the upswing of geologic tumult, Bob Christiansen of the U.S. Geological Survey said that the volcanic eruption in sparsely populated southwestern Washington, "is not a major danger to anyone who observes the rules."

Those rules include a ban on travel anywhere near the mountain, which ended more than a century of silence Thursday when ash spewed out of craters and huge cracks on the summit. It is the first volcano to erupt in the contiguous United States in 60 years.

No injuries or major property damage has been reported as of nightfall today, but authorities said volcanic ash was drifting as far as 25 miles east of the mountain.

Geologists expressed concern that mudslides, avalanches and heavy run-off from melting snow could flow suddenly in to Swift Reservoir, about eight miles south of the peak.

But officials of Pacific Power and Light, which operated hydroelectric facilities at Swift Reservoir and two other dams within 30 miles downstream, said there was no danger of the 300-foot-high earthen dam overflowing.

Low-hanging clouds obscured Mt. St. Helens' summit throughout the day, so authorities could not determine whether there had been continued growth in a major crater, last estimated at 250 feet wide, or in a series of nearby fissures, one of which was reported to be three miles long and up to 1,000 feet wide.

"We have seen no lava flows," Christiansen said, although there is "a very reasonable possibility that we will . . ."

He added that there have been indications of pyroclastic flows -- masses of hot, dry rock debris that move like fluid because they are mixed with hot air and other gases.

There also have been mudslides stretching for thousands of feet down the steep, snow-covered mountain, as well as numerous avalanches triggered by the fall of volcanic ash, he said.

Air space above the volcano was closed to all but government planes. and the federal observers radioed back to command headquarters in Vancouver that each explosion within the mountain was sending up a plume of steam and ash -- as well as such gases as sulphuric dioxide, easily identified because of its foul smell.

"The plumes are classic mushroom shape," one airborne observer reported at midafternoon, with "considerable air turbulence from heat of plumes."

Most of the plumes reached an altitude of 15,000 to 17,000 feet above sea level, and some extended to 20,000 -- roughly two miles above the summit.

The massive explosions within the mountain began about 2 a.m. Thursday, accompanied by a series of earthquakes measuring from 3 to 4.5 on the Richter scale. During the next 12 hours, about 25 explosions were detected, some only seconds apart, and Christiansen said the volcano seemed to be settling into a pattern of "continuous or uniform activity."

But like other geologists monitoring the volcanic eruption, Christiansen said he could not predict what would happen next at Mt. St. Helens.

Although experts described Mt. St. Helens' sputterings as relatively minor in comparison with some of the comparison with some of the world's past volcanic events, it was a cause of major excitement in the Pacific Northwest. v

The mountain was the major topic of conversation in Vancouver's shops and restaurants, and there were even hastily printed T-shirts, proclaiming "I erupted at Mt. St. Helen's" and "Mt. St. Helens: Lava Or Leave It."

Mt. St. Helens has been classified as dormant because it has not erupted for more than a century. However, two U.S. Geological Survey experts, Donal Mullineaux and Dwight Crandall, warned two years ago that the mountain was "an especially dangerous volcano" and that a major eruption could directly or indirectly endanger 40,000 people.

Local residents, however, seemed relatively unfazed. Harry R. Truman, 83, operator of the St. Helens Lodge high on the mountain, refused to leave. "That mountain just doesn't dare blow up on me," he said.

"Anyway, I've got a secret place up here on high ground where I hid a grubstake and two kegs of whiskey, and there's no way I'm going anywhere."

Authorities said that because of the lodge's location, Truman was unlikely to be cut off.

Dave Smith, owner of the Spirit Lake Lodge, which caters to seasonal hunters and fishermen, said the eruption could be the best thing that ever happened to him. "As far as I'm concerned, it would be a bonanza for us because of the tourist trade. We need a break like this as long as it don't blow its cork entirely and wipe us out."

In historic gelogical terms said Don Swanson of the U. S. Geological Survey, the tumult of Mt. St. Helens has been far less significant than the periodic eruptions at California's Lassen Peak between 1914 and 1920 -- the last lava flow from a volcano in the contiguous United States.

The new activity also dwarfed by many other past eruptions in the Cascade range, including at least 23 incidents during the past 10,000 years at Mt. Shasta in northern California and 11 at Mt. Ranier near Seattle.

But none of the past activity in the Cascades can match the massive explosion of Mt. Manzama in what now is southern Oregon. In fact, Mt. Manzama no longer exists. It was blown apart 7,000 years ago, producing the hole now filled with water 1,700 feet deep and known as Crater Lake.