VANCOUVER — Four months after Mount St. Helens stirred back to life, the bulging new dome inside the crater has ballooned 350 feet high and now holds enough solid material to fill Madison Square Garden 134 times.

At its peak, molten magma was being transformed into new rock that was pushing skyward at a rate of 10 meters per day.

And earlier this month, an unexpected but significant explosion - the biggest since October - caught researchers by surprise and appears to mark some sort of transition on the sleeping giant's path to regrowth.

"It makes me think a lot differently about the range of possibilities for the future," geologist John Pallister said today. "We were anticipating a different event.

"Figuring out what it means will take some time."