Magma oozes out of a dome in the Mount St. Helens crater Tuesday evening, in Mount St. Helens, Wash. The magma, that has been rising inside the mountain after weeks of earthquakes and steam eruptions, finally pushed its way to the surface, forming the new dome just behind the existing one.

Mount St. Helens, Wash. — Volcanic rock has flowed to the surface of Mount St. Helens' crater, creating a new lava dome after weeks of seismic activity, a geologist said Tuesday.

Scientists had known for days that magma or molten rock was nearing the surface, as a bulge grew on the south side of the existing 300-metre lava dome and the increasingly hot rock gave off steam as it met water and ice in the crater. The bulge is now considered a new lava dome, the scientists said.

“Now that we have new lava at the surface, we're comfortable saying” that dome-building has resumed at the volcano, U.S. Geological Survey geologist Tina Neal said.

The bulge had risen at least 100 metres since scientists noticed it Sept. 30.

Geologists said there is still a chance of explosive ash eruptions from the 2,550-metre mountain, which is about 280 kilometres south of Victoria.

Because there remains the possibility of an eruption occurring with very little warning or time to raise the alert level, the immediate area around the volcano will remain closed, the organization said.