ANCHORAGE, Alaska (AP) — A volcano has erupted with little warning on an island in Alaska, sending an ash cloud at least 30,000 feet high.

The Okmok Caldera erupted late Saturday morning. Seismologists at the Alaska Volcano Center detected a series of small tremors hours before.

Okmok is located on one of Alaska's Aleutian Islands, 60 miles west of the busy fishing port of Dutch Harbor on Unalaska Island.

Two planned flights from Unalaska were canceled in response to the eruption, said Jerry Lucas, a spokesman for PenAir, the primary airliner serving the area.

Geophysicist Steve McNutt says the 3,500-foot volcano last erupted in 1997. He says the volcano has shown signs of increased activity during the last few months.