ANCHORAGE - Mount Veniaminof, one of Alaska's largest and most active volcanoes, spewed hot rocks and lava that was clearly visible to residents more than 20 miles away.
The volcano's increased activity was noticed Thursday night after a decrease in seismic activity during the morning, said scientists at the Alaska Volcano Observatory.
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"This kind of activity, while it would certainly be quite dangerous close up, has not led to bigger explosions," John Eichelberger, coordinating scientist for the observatory, said Saturday. "It is not cause for great alarm because this is pretty typical behavior of this volcano."
The volcano, located on the Alaska Peninsula 480 miles southwest of Anchorage, was upgraded from yellow to orange on Jan. 10 after a very weak seismic tremor was observed on Jan. 1. The tremor increased in magnitude over the next week. Orange indicates that the volcano is erupting or may erupt at any time.
Veniaminof has erupted at least 12 times in the past 200 years. The most significant eruptions occurred between 1993 and 1995 when the volcano produced steam and ash and a small lava flow was extruded from a vent. The lava flow melted snow and ice, producing an oval-shaped ice pit.
Minor ash-producing explosions occurred in 2002 and 2004, as well as in recent weeks. In 1939 following an eruption, several centimeters of fine ash fell on Perryville, about 22 miles away.
On Jan. 8, satellite images showed unusual heat near the volcano's summit. The volcano also has been producing small ash emissions, some reaching nearly 13,000 feet above sea level, nearly continuously since the second week in January. The ash could be a problem for low-flaying aircraft. The volcano has numerous cinder cones.
Scientists say the seismic activity this time is slightly more than the previous episode, which ended last September.
Veniaminof has acted up before in a big way, but not recently.
"It had a gigantic explosion about 4,000 to 5,000 years ago, which is not that long as far as volcanoes go," Eichelberger said.
While much less dramatic, the more recent eruption could provide some interesting opportunities for scientists. The Alaska Volcano Observatory monitors the volcano through the use of numerous seismic recording devices. The observatory also has a Web cam set up about 25 miles from the volcano.
"Perhaps we will see some pretty displays on the Web cam," Eichelberger said.