VANCOUVER, Wash. (AP) - The Cascades Volcano Observatory in Vancouver says Mount St. Helens is steaming a little Wednesday as a low-key eruption is now in its fourth year.

To see a real-time picture of the mountain, click here.

Magma has been slowly pushing into the crater, building a lava dome since the fall of 2004 with occasional small quakes and steam bursts.

There was some unusual steaming on Sunday when the mountain was rattled by two quakes with magnitudes of 2.7 and 2.9.

Geologist John S. Pallister was flying over the mountain Sunday when he spotted something unusual.

Pallister, a private pilot who works in the hazards section of the U.S. Geological Survey's Cascades Volcano Observatory, noticed a line of steam coming from a zipper-like fracture line atop a growing lava dome in the crater of the southwest Washington volcano.

"It was interesting enough to take some pictures," Pallister told The Columbian newspaper of the Sunday flight.

After landing, he learned that a 2.9-magnitude earthquake had registered on seismographs at the observatory in Vancouver. That was followed by a small tremor that lasted nearly an hour and a half, an unusually long period, punctuated by a second quake of 2.7 magnitude - all in the same period in which he saw the steam.

Along with the shake, rattle and roll, tiltmeters registered alternate ground swelling and deflation near the lava dome, which has been growing in the crater since the fall of 2004.

All are typical signs that magma, superheated gases or both are moving through conduits beneath St. Helens, which blew its top with devastating force on May 18, 1980, leveling 230 square miles of forest and leaving 57 people dead or missing.

The last noteworthy tremor at the volcano lasted 55 minutes on Oct. 2, 2004, and was much more powerful, registering on seismometers from Bend, Ore., to Bellingham and causing a hasty evacuation of the Johnston Ridge Observatory five miles north of the crater.

No evacuations have been ordered this time - seismic activity was generally unremarkable in the days following the episode Sunday and the likelihood of a major eruption seemed low. But Cynthia A. Gardner, scientist in charge of the volcano observatory, said Tuesday that scientists had quit venturing into the crater.

"We're going to back off of that for the next couple of days," Gardner said.

She said the precise cause of the recent activity was not entirely clear.

"The settling of the growing lava dome might have caused some fracturing and might have changed the subsurface openings so that water was either being squeezed out of openings or opening new areas," Gardner said.

The last precise measurements, drawn from images in July, indicated the latest eruptive phase has pumped 123 million cubic yards of material into the crater. The rate has slowed considerably, but the episode Sunday showed that could change at any time, Pallister said.

"Rumors of an early end of this eruption are once again shown not to be the case," he said. "It's still got some surprises."