Mount St. Helen erupted today with a mighty blast, sending a column of ash 10 miles into the air and blotting out the sun for more than a hundred miles. At least eight persons were killed on the mountainside.

At 8:32 a.m., a massive explosion felt more than 200 miles away in Canada, signaled the beginning of the volcano's most spectacular eruption since last March 27, when the mountain began sending out steam and ash for the first time in 123 years.

Military helicopters flying over the mountain spotted several cars overturned near a Meyerhaeuser Co. logging camp 12 miles from the mountain, and at least five bodies were seen in the cars, said a spokesman for the state Department of Emergency Services in Olympia.

Two of the bodies were recovered by an Air Force Reserve helicopter. Air Force Lt. D. E. Schroeder said the victims were killed by heat, but no details were immediately available.

At least three persons were missing, and the state emergency services spokesman said there could be more fatalities.

Fine ash and pumice boiled out of the volcano's crater and a vent on the mountain's northwest slope. Within an hour the morning sky was so dark that automatic street lights came on in Walla Walla, more than 150 miles to the east.

"We could see it coming," said Sheriff's Sgt. Larry Gamache in Yakima County, 80 miles east of the volcano."We knew about 9:18 a.m. that we had a major eruption. Within about 10 or 15 minutes we could view an extremely large cloud cresting the Cascades.

"It gradually went from a bright sunlight to gray to muddy brown to black. It's just as dark as the darkest night you've ever seen."

About 120 familes were evacuated from the town of Toutle and nearby low-lying regions as mudflows entered both forks of the Toutle River on the north Flank of the 9,677-foot, snow-covered mountain in Southwestern Washington. State patrolmen said a brown wall of water as high as 20 feet swept down the river, destroying several bridges as well as houses along the banks.

"The devastation on the mountainside is incredible," said Air Force Lt. Schroeder. "Trees are knocked down, animals are standing around in shock, covered with ash."

Ash from the eruption fell 500 miles to the east in Great Falls, Mont., and in northern Idaho, 300 miles from Mount St. Helens, some roads were closed because the ash was causing poor visibility.

U.S. Geological Survey spokesman Worner Gerhard said Mount St. Helens' peak had been reduced to about 9,100 feet by the force of the explosion. He and a Forest Service Spokesman said the flow of the hot debris from the crater was reaching Spirit Lake at the north end of the mountain, making it bubble and boil.

There was no word on the whereabouts of Harry Truman, a crusty 85-year-old who had refused to leave his Spirit Lake resort. More than 30 feet of mud and debris was believed to have covered the area where Truman operated a 40-acre resort.

A dispatcher in the Cowlitz County Sheriff's office said there were reports of lava flowing down Mount St. Helen's slopes, but U.S. Geological Survey scientists could not immediately confirm them.

Scientists have feared for weeks that a major avalanche from the bulging north side of the mountain could dump tons of rock and ice into Spirit Lake, sending a mudslide rushing down the valley.

But today, those scientists apparently were as much in the dark as Walla Walla as to what exactly was happening within Mount St. Helens.

A Geological Survey spokesman said the volcano had been erupting continuously since the first explosion this morning. There has been a pyroclastic flow -- high-velocity emissions of hot ash, rock debris and gas, he said, but no flow of magma, or lava, had been confirmed.

The spokesman said there was no way to say whether the volcano was in danger of a full force eruption and flow.

The height of the volcanic plume had decreased to 43,000 feet by late afternoon, but the spokesman said a decrease in the size of the plume does not necessarily mean a decrease in the strength of eruptions.

Joe Sullivan, a Toutle resident who saw the eruption from a vantage point about three miles away, said a section of the mountain "just moved sideways and the whole thing went up."

"It scared the hell out of me," said Sullivan, who had ventured up the mountain with his wife and two friends on a picture-taking trip.

They said the explosion sent up a cloud of pitch-black ash stabbed through by lightning bolts along the crater's rim. The four jumped into their pickup and raced down the mountain as fast as Sullivan could maneuver the winding roads.

The lightning, created by chemical reactions in the vocano, started a 3,000-acre forest fire two miles east of Mount St. Helens and two smaller fires, the U.S. Forest Service reported.

Roads were closed throughout Washington state as falling ash obscured visibility and pumice coated the road "like BBs," making driving treacherous. Undaunted sightseers created massive traffic jams heading toward Mount St. Helens -- to no avail because roadblocks were set up 50 miles from the mountain.

Airspace over the volcano also was closed to traffic by the Federal Aviation Administration, but not before Washington Gov. Dixy Lee Ray flew over the erupting mountain. Ray said she got "an excellent view" and called the situation "both exciting and worrisome."

"It's spectacular. It's a real eruption. There's no question about it," she said. Her prime concern, she added, was whether volcanic ash would jeopardize water supplies in the state. Supplies for the metropolitan area of Portland, Ore., to the south were spared for the moment by winds that blew the drifting ash east.

In Kid Valley, 35 miles west of the volcano, tourist store owner Stanley Lee said "the ash is thicker than hell -- it looks like fog."

"People are headed out -- the road is jammed," he said. "I'm not scared -- yet." But he added, "I might leave just because there is no reason to stay here now that they have all the roadblocks up.

"My business is ruined. I'm going to take a holiday."