Clouds obscured a short steam burst above Mount St. Helens early today, on the eve of the first anniversary of the volcano's deadly eruption.

At 8:32 a.m. on May 18, 1980, the reawakened volcano shuddered with two violent earthquakes that ruptured the summit and set off a huge landslide from its bulging north flank.

A short, 13-minute seismic signal detected at 5:50 a.m. today at the University of Washington in Seattle indicated a steam plume was apparently rising from the peak, but otherwise geologists said Mount St. Helens was "very quiet."

A weekend of celebration took place in several towns in southwest Washington.

At Castle Rock, a minor eruption of 1,000 ping pong balls out of a replica of the mountain sent youngsters scurring for the rolling debris, redeemable for merchandise at local stores.

"We're not celebrating the volcano," Chamber of Commerce president Randi Beemis said of the observance. "We're celebrating the fact that people survived the volcano."

Toutle held a noisy, patriotic parade through the streets while concessionaires had a field day selling souvenirs.

Paul Sears, 73, a logger crowned king of the Toutle's "Volcano Daze," rode on a float beside a home-made cone and a little pine tree and declared, "I seen the old mountain when it was beautiful and I sat and watched it be destroyed."

A different sort of memorial was held in Silver Lake, where fans of the late Harry Truman gathered in celebration of a book about to be released on the life of the 84-year-old man from Mount St. Helens' slopes. They drank Truman's favorite drink, Schenley's and Coke, and dined on one of his favorite dishes, venison.