A volcano erupted Saturday with little warning on a remote island in Alaska, sending residents of a nearby ranch fleeing from falling ash and volcanic rock.

The Okmok Caldera erupted late Saturday morning, just hours after seismologists at the Alaska Volcano Center began detecting a series of small tremors.

The explosion flung an ash cloud at least 50,000 feet high, said geophysicist Steve McNutt.

Nine people, including three children, were at Fort Glenn, a private cattle ranch six miles south of the volcano on Umnak Island, located in the western Aleutians. They managed to call authorities on a satellite phone before losing their connection, according to the Coast Guard, which had a cutter en route to the island, about 860 miles southwest of Anchorage.

Coast Guard Petty Officer Lee Goldsmith said those at Fort Glenn reported rock and ash falling around them.

A Coast Guard cutter set out for the ranch but wasn't expected to arrive until Sunday morning, Goldsmith said. Because of the ash and rock, the Coast Guard could not send aircraft, Goldsmith said.

The Fort Glenn residents were planning to use a small private helicopter to fly to nearby Unalaska Island, which is separated from Fort Glenn by a five-mile channel.

"They can only carry one person at a time in that helicopter," Goldsmith said.

Okmok is 60 miles west of the busy fishing port of Dutch Harbor on Unalaska Island. Ash was reported falling in the region, McNutt said.

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.

The 3,500-foot volcano last erupted in 1997, according to McNutt. The volcano has shown signs of increased activity during the last few months, he said.

Previous eruptions have typically produced lava flows, but the volcano center could not immediately determine if that had occurred in Saturday's explosion, McNutt said.