"Hopefully this won't happen in our lifetime, but eventually something will happen," said Dr. Alexander Malahoff, director of the Hawaii Undersea Research Laboratory at the University of Hawaii.

Malahoff said the sea wave would "wipe out" Waikiki and much of the coast of Oahu, causing countless billions of dollars in damage. "We have to be prepared for it," he said.

Malahoff issued his warning at a news conference here describing the undersea exploration of the emerging volcanic island 21 miles off the coast of the Big Island. The exploration was sparked by a series of underwater earthquakes in July - thousands over a period of just a few weeks - that attracted the attention of scientists.

"This is an island in the womb," said Malahoff. "It will be the next island to arise. ... This is the only time we will be able to see a real-life island forming."

Although countless islands are forming in the world's oceans, Loihi's proximity to Hawaii makes it the easiest to study, said Malahoff.

The July earthquakes are part of the activity that eventually - perhaps in 50,000 years - will cause the mountain to surface and form the next Hawaiian island. "We'll be seeing more and more activity."

The earthquakes in July caused huge blocks of rock to tumble as the top of Loihi collapsed. If the collapse had been quicker, Malahoff said, it would have caused a tsunami with potentially catastrophic effects for Hawaii.

Although Honolulu now would have only a few seconds notice of an advancing tsunami caused by Loihi, Malahoff said future technology might make it possible to more accurately predict eruptions and provide far more notice. "Hopefully, we'll have some sensors in place in the next few years."

He compared the danger to Honolulu to the threat posed to Seattle by Mount Rainier. "Sooner or later, Mount Rainier will erupt, and what's going to happen to Seattle?"