ANCHORAGE, Alaska — A lava flow has been spotted on an Alaska volcano that recently became active again.

Alaska Volcano Observatory scientists say witnesses aboard the state ferry Tustumena saw the lava flow and fountaining on Mount Veniaminof (VEN'-ee-ah-mean-off) Monday morning.

Scientists say satellite images obtained Sunday shows the lava flow is about one-half-mile long on the 8,225-foot (2,500-meter) volcano, one of Alaska's most active.

The observatory last week increased the threat level of Veniaminof from yellow to orange. That color designation indicates sudden explosions could send ash above 20,000 feet (6,100 meters) and threaten international airplanes.

The volcano erupted for several months in 2013. Other recent eruptions occurred in 2005 and between 1993 and 1995.

Veniaminof is 480 miles (772 kilometers) southwest of Anchorage on the Alaska Peninsula. Perryville, a town of about 100 people, is 20 miles southeast of the volcano.