Sisters, Ore. -- The swelling bulge on the west flank of the South Sister volcano is slowing and geologists say there are no signs that the uplifted region will erupt in the near future.

The latest statistics from instruments monitoring the bulge indicate that the uplift has slowed to about half its former rate of an inch or so a year.

Geologists think the bulge is being created by magma being pushed into a chamber about four or five miles underground, and its slowing means less of the liquid rock is flowing upward. They don't know why the rate of magma has seemed to ease.

"It's possible it's slacking off, but over the coming years the rate will change," said geologist Willie Scott of the at the Cascades Volcano Observatory in Vancouver, Wash. "That's why we want to continue to monitor it as closely as we can, because we're seeing a phenomenon that we haven't been able to study before and we want to see where it goes."

Scientists have monitored the Central Oregon volcano since 2001, when a comparison of newly acquired satellite measurements showed that a 10-mile-wide chunk of the mountain had risen more than four inches over the preceding four years.

Since then, numerous instruments have been set up around the mountain, and geologists are using three different techniques to measure ground movement.

The deformity is centered just west of the mountain, but the affected area stretches as far northwest as Dee Wright Observatory on the Old McKenzie Highway and as far southeast as Devil's Lake on the Cascades Lake Highway.

A swarm of more than 300 tiny earthquakes struck the area in March 2004, but the bulge has since been quiet. Only five quakes were recorded this year, none with a magnitude greater than 1.5.

By comparison, thousands of earthquakes as strong as magnitude 4 or 5 struck the area around Mount St. Helens in the months leading up to its eruption.

"There are times when there's deformation like this that goes on and leads to eruption," Scott said. "And then there's times when the deformation just reverses and goes away. The possibilities are endless."