The Alaskan Volcano Observatory (AVO) reported lava flowing from two of the state's volcanoes Tuesday, placing the mountains on the second-highest alert status and prompting concerns that air travel may be affected by volcanic ash.

The volcanoes Cleveland and Pavlof are both along the Aleutian Island chain, where a significant volume of air traffic flies overhead. There is a code Orange aviation warning at both volcanoes, the AVO reported.  

Cleveland Volcano has been erupting for nearly three weeks and was placed on a code Orange alert earlier this month after gas and volcanic ash began billowing from the summit. However, Tuesday's report of a 32-foot-wide (100 meter) lava flow extending  about a mile (1.5 kilometers) down the mountain's southern flank was the first report of lava from Cleveland since the volcano began erupting May 4.

The eruption at Pavlof Volcano, the taller of the two mountains, was confirmed Tuesday following an increase in seismic activity and presence of intense elevated surface temperatures. Reports from pilots and satellite imagery reveal a flow of lava from Pavlof running down the mountain's north face for about a third of a mile (500 meters).

Cleveland (5,675 feet; 1,730 meters) and Pavlof (8,251 feet; 2,515 meters) are nearly symmetrical stratovolcanos about 400 miles (645 km) apart.

Both are considered among the most active volcanoes in the region, Cleveland having erupted at least 22 times in the last 230 years and Pavlof having erupted a dozen times since 1980.

Cleveland is very far west along the island chain and there are no ground instruments monitoring the isolated volcano, meaning it takes longer to realize an eruption is occurring there. Pavlof is closer to mainland Alaska and is monitored by ground equipment.

While their remote location poses little risk to people on the ground, the erupting volcanoes can potentially have serious consequences for the high-volume air traffic over the region.

CNN reported that 90 percent of air freight from Asia to Europe and North America flies over Alaska airspace, and hundreds of flights fly through Anchorage's air space daily.

"We think of the Aleutian Islands as being remote and desolate" John Power, a scientist from the U.S. Geological Survey, told CNN, "but when you come up to 30,000 feet we are talking about 20 to 30,000 people there every single day."