Palls of steam rose out of the crater on Tuesday and Wednesday as the peak in northwestern Washington state vented as lava rose to the surface to formed a new dome, the experts said.

US media showed images of glowing red lava rising to the surface of the volcano.

"We have magma on the surface and are entering a new period of dome growth on the mountain when it's common to have periods of quiet lava explosions," said Samantha Magsino of the Washington Geological Survey.

The US Geological Survey said the lava was at a very shallow level following intense activity in the mountain for almost three weeks.

"Abundant steam continued to rise from the fin area to the crater rim, from which it was dispersed southeastward by strong winds," the USGS said on its website.

But earthquake activity around the peak remained at low levels, indicating that an eruption was not imminent, scientists said.

The mountain erupted dramatically in May 1980, killing 57 people and covering swathes of the US northwest in a thick blanket of ash.

Scientists said that any explosion of the peak, which last saw an eruption in 1986, was not likely to match the scale of the 1980 event.

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