Mount Redoubt showed increased unrest Sunday as the volcano continued to rumble and grumble and produced a substantial ash and steam plume.

On Sunday, scientists said there was a marked increase of seismicity at the volcano about 100 miles southwest of Anchorage.

"It is a bit dynamic right now," said Stephanie Prejean, a geophysicist with the U.S. Geological Survey at the Alaska Volcano Observatory.

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Prejean said the day began with more continuous ash emissions. In the afternoon, there was an ash and steam plume that went to 18,000 feet.

The volcano has been in what is called a dome-building phase as it grows a lava dome in its crater.

The dome has grown considerably in recent weeks, AVO scientists said. A tongue of lava now has advanced about 550 yards down the Drift Glacier Gorge.

The volcano had its last major explosion on April 4. Since then, the dome has been growing. It first erupted on March 22. That was followed by numerous large explosions, some sending ash plumes more than 50,000 feet into the air.

During the dome-building phase, scientists with the AVO have been busy collecting new data, including taking thermal images, radar profiles and geologic observations.

The observatory continues to log seismic data and periodically measure the volcano's gases.

According to scientists, the lava dome that is growing is similar to the one that grew in early 1990, the last time the volcano was active. As the magma pushes up through the crater, it creates rock falls, which have occasionally generated minor, localized ash and steam plumes.

Scientists doing infrared measurements of the lava dome found maximum temperatures of 790 degrees Fahrenheit. The temperature does not reflect the temperature of the magma as it emerges from the vent, but is a measure of the cooling crust of new rock that surrounds the extruding magma. The lava is considerably hotter, about 850 degrees Fahrenheit.

The mudflow that ensued after the April 4 explosion was large enough to extend across the entire Drift River Valley. It toppled trees and left high-water marks more than 30 feet above the river channel, according to observatory scientists.

The threat level remained at orange Saturday, meaning that the volcano is exhibiting heightened or escalating unrest with increased potential of eruption, or that an eruption is under way with no or minor volcanic-ash emissions.

In late 1989 and early 1990 the volcano was active for four months. The longest hiatus between explosions was 36 days. Saturday marked the 28th day.