The island, thought to have been formed during the Pleistocene Ice Age, is located between the Santa Barbara Harbor and one of the existing Santa Barbara Channel islands in California. The island is some 31 miles long, 3 miles wide and projects 660 feet above the channel floor.
"We came across this while we were studying earthquake hazards," said Edward Keller, professor of geological sciences and environmental studies at the University of California at Santa Barbara. "All of the indications suggest it is an island located about 100 meters below the surface."
Those indications include the fact the structure seems to have sea cliffs, Keller said. The topography is also rough, as though it had been eroded by land processes rather than marine processes, which typically leave smooth contours on geographic features.
Keller named the island Isla Calafia, which comes from a Spanish romance novel written around 1500. Calafia was a mythical place ruled by a beautiful female warrior and could have been where the name California comes from, he said.
Isla Calafia is located on the highest portion of a ridge along the ocean floor. The ridge extends from Point Conception north of Santa Barbara to South Mountain near Ventura, Calif. Keller said.
In his quest to better understand earthquake threats, Keller was studying high-resolution topological maps provided by the Monterrey Bay Aquarium Research Institute. Keller said those maps provide topographical data "that is as good or better than what we have for land."
The maps are generated by what he calls "a kind of sophisticated fish finder" that records elevation data on the ocean floor.
The island sits between two key earthquake faults. Those faults can cause earthquakes of 7.5 magnitude as well as tsunamis or sea waves churned up by submarine earth movement or volcanic eruption.
Keller said other dangers lie around the island to its east and west.
"We think there are large oil fields out there and such fields tend to have gas emissions," he said. "Those pockets of natural gas could erupt one day to pose hazards to passing ships."
He also said his research team is studying some unknown geographic features they have detected not far from the island.
"As I understand it Calafia would have been exposed at the glacial maximum about 18,000 years ago but probably was submerged by about 15,000 years ago," said John Johnson, curator of anthropology at the Santa Barbara Museum of Natural History.
If the island was ever above water, could people have ever seen it?
"The first people to enter the Americas would have been unlikely to have seen Calafia if migration occurred after 15,000 years ago, as most archaeologists suspect," said Johnson. "The earliest evidence for people on the Santa Barbara Channel Islands comes from the Arlington Springs Site on Santa Rosa Island, which has yielded a date on human bone of 13,000 years before present."
Keller will present a paper on Isla Calafia at the national meeting of the Geological Society of America in Boston on Nov. 4 and 5.