SAIPAN, Northern Marianas — A volcanic eruption near the Pacific's Northern Mariana Islands shot clouds of ash and vapor nearly eight miles into the sky, federal scientists said.

The eruption occurred early Saturday and appeared to come from an underwater volcano off Sarigan, a sparsely inhabited island about 100 miles north of the U.S. commonwealth's main island of Saipan.

The Northern Marianas are about 3,800 miles southwest of Hawaii.

USGS volcanologist Game McGimsey said Sunday that scientists are still trying to pinpoint the source but evidence is pointing to an underwater mountain.

"People on the island (Sarigan) heard a loud explosion and almost immediately there was a heavy ash fall which turned to a light fall fairly quickly," McGimsey told The Associated Press. He said there was no ash in Saipan or Guam.

The eruption was fairly brief and no other volcanic clouds have been detected, said McGimsey, who is based in Anchorage, Alaska. Scientists don't know if the undersea activity is continuing.

Satellite images showed the cloud reaching to 40,000 feet. But the USGS said it was largely water vapor and strong winds were dispersing it.

McGimsey said researchers flew over the area Sunday and spotted discolored water presumably over the volcanic vent, estimated at 1,000 feet beneath sea level.