This city awoke today to find itself a gooey mess -- covered with a slippery, brown-gray paste that stuck to streets and windshields and splashed cars and pedestrians.

Mount St. Helens erupted Thursday night for the third time in less than a month. Ash rose 10 miles in the air and was carried 40 miles downwind, mixing with rain to settle -- about an eighth of an inch deep -- on homes and the local water reservoir.

Federal emergency officials said there were no reports of deaths or serious injuries, but the continued eruptions have transformed the mood here from one of bemused detachment to concern.

"I think the people in the city of Portland first viewed the volcano as a sideshow," said Sam Thomas, spokesman for Portland Mayor Connie McCready. "People sat up on hills and wated the first eruption" May 18. "After that they saw the devastation, and the people began to take it seriously as a very, very dangerous thing. The anxiety level here has increased. It's [the mountain's] there, and it's not going to move, and we're going to have to live with it."

The scientists and federal officials said today they could not predict when Mount St. Helens might blow up again. The last time the volcano was active -- in the 19th century -- eruptions continued for more than 14 years.

"People have to recognize that they could be in for a long period of eruptions, said Craig Weaver, a geophysicist with the U.S. Geological Survey (USGS). "It does appear that the volcano may be in a state of eruption for 20 years. In geologic time, that's like a second, a brief blink of the eye."

Weaver and others said today that lava sloshing beneath the earth's surface is causing the latest eruption, but they do not yet know how or why.

They have observed one unexplained phenomenon, however, that they hope may help them determine when the next explosion is about to occur.

Before each of the three major eruptions (May 18, May 25 and Thursday), instruments measuring tremors below the volcano's surface have recorded a sudden sharp drop in the rumbling -- an "ominous quiet," a Federal Emergency Management Agency spokesman charactericized it.

The drop that occurred Thursday night was followed by the eruption and tremors so strong that physicists and geologists at first believed that there had been an earthquake in the volcano similar to the one that triggered the first and most devastating blast, on May 18.

That eruption, which blew a huge chunk out of the north side of the mountain, killed 24 people and left 46 missing and presumed dead, clogged rivers with debris and blanketed some eastern Washington farming towns with up to 2 inches of hard-to-remove, powdery dry ash.

A spokesman at the University of Washington said the May 18 eruption was like champaign flowing from a bottle that has been shaken. The subsequent eruptions have been more like what happens when a beer can's top is popped," she said.

This latest eruption began about 9:11 p.m. (PDT) Thursday, according to federal officials. People in the vicinity of Mount St. Helens were warned of what was to come by the stench of sulfur. Airline pilots were the first to see or hear the blast.

"It looked like an atomic bomb," said one.

Small rocks about the size of marbles spat out on the countryside around the volcano, and wind carried ash as far south as Salem, Ore., and as far east as Pullman, Wash. There were scattered reports the ash drifted as far north as Seattle.

The mountain puffed clouds of ash intermittently every two or four minutes for about two hours before the dark plumes began to subside. By about 1:30 this morning, according to federal officials, the clouds had turned from ash to steam. Although it appeared the crisis had passed, authorities warned about a million people in the region to stay indoors or wear masks if they decided to go outside.

Thomas, the spokesman for Mayor McCready, said the city is concerned that if it is hit by repeated ash deposits its water supply might be polluted and its sewers clogged.

For the most part, Portland followed its normal Friday routine. Masks were worn by some residents who ventured out, including one meter maid who refused to let the sticky mush keep her from ticketing illegally parked cars. A 15 mph speed limit was imposed and a limited state of emergency declared.

City workers hosed down the streets, sidewalks and storefronts along the route of the annual Rose Festival parade, scheduled for Saturday. And Portland appeared determined that the show go on.

At Waterfront Park on the Willamette River, sailors from the navies of the United States, Canada and New Zealand were up early to hose down their vessels. Nineteen ships are docked in Portland for the festival.

None of the ships reported any mechanical or equipment problems related to the ash. Lt. Doug Steudler, an engineer on the destroyer Elliott, said the U.S. ships are on a four-hour standby alert to leave if the volcano acts up again.

The eruption occured just a few hours before midnight -- and Friday the 13th. Scientists had said that the moon's tidal pull on the volcano would be slightly greater than normal today, and had crossed their fingers, hoping that the tempermental mountain would not give a boost to the superstitious.

"If it blows up on Friday, it will set science back 10 years," a USGS geologist had said.

Seattle, which thus far has avoided any serious side effects from the eruptions, earlier this week regarded Mount St. Helens with some amusement. Stores sold Mount St. Helens T-shirts and bumper stickers that declared Washington the "Ash Tray of the Pacific Northwest." A hotel peddled vials of volcanic ash for $3 each and in its seafood restaurant it offered an after dinner drink it called "Coffee St. Helens, and explosive blend of Grand Mariner, Irish Mist and Tia Maria."

But Seattle did not think the volcano was all that funny today as reports of a sudden drop in tourism began to flourish here. Officials said six conventions scheduled for Seattle had been canceled since the May 18 eruption.

Washingon Gov. Dixy Lee Ray told tourist industry officials they had been hit by an "unfortunate fallout of fear."

"We're getting killed," said Gary Walker of the Seattle-King County Convention and Visitor's Bureau. "And it's not an ash problem. It's a public relations problem. No one has any conception of where the mountain is. As far as they are concerned, Mount St. Helens is in the middle of Seattle."