The initial eruption on Mount Cleveland, a volcano about 940 miles (1,510 km) southwest of Anchorage, occurred on Monday, showering ash on nearby fishing vessels, according to the Alaska Volcano Observatory, a joint federal-state office that monitors Alaska's plentiful volcanoes.

Mount Cleveland, one of Alaska's most restless volcanoes, has continued to spew clouds comprised mostly of steam and there is what appears to be a small lava flow trickling from the vent, the monitoring group said.

"It erupts so frequently that it's not a surprise when it erupts," said Peter Cervelli, research geophysicist for the Alaska Volcano Observatory, noting that Mount Cleveland, which rises to 5,676 feet (1,730 m), erupted last year.

Cervelli called the proximity of the two eruptions a coincidence and said the two events are unrelated.

The events at Okmok, a 3,520-foot (1,073-metre) volcano on Umnak Island, have been more dramatic, prompting the Alaska Volcano Observatory to keep staff at work around the clock.

Explosions from Okmok have recurred regularly since the initial eruption on July 12, sending steam and ash up to 30,000 feet (9,100 m) in the air and keeping the remote island's 10 evacuees from returning home.

If Okmok remains true to historical patterns, eruptions there are likely to continue for weeks or even months, according to projections from the Alaska Volcano Observatory.

In the fishing hub of Unalaska/Dutch Harbor, located 65 miles (105 km) northeast of Okmok, ash has turned skies hazy and prompted air-quality advisories from the Alaska Department of Environmental Conservation.

Airline pilots and mariners passing through the area are also under advisories to avoid the ash. (Editing by Daisuke Wakabayashi and Cynthia Osterman)