Oct. 27, 2005 — Noisy popping rocks hauled up from the deep Pacific seafloor off northern Mexico appear to be from a very young undersea volcano, say U.S. and Mexican geologists.

Some of the weird and scientifically valuable gas-charged volcanic rocks were first discovered in the same area in 1960, but no one had been able to find them again until now.

It took some careful and persistent dredging of the 10,500-foot-deep (3,200-meters) seafloor by a bi-national crew of students and researchers near what is called Popcorn Ridge, 200 miles south of San Diego near Guadalupe Island, to relocate the remarkably loud rocks.

"People don't know how many volcanoes there are off the coast here," said Dana Vukajlovich, one of the chief scientists on the cruise, organized by the Scripps Institution of Oceanography at the University of California, San Diego.

Another Scripps oceanographer, Dale Krause, who first found the popping rocks 45 years ago.

The rocks pop because they contain pressurized pockets of gases that had bubbled out of the rock when it was molten and erupting from a submarine volcano, explained Vukajlovich.

But under intense pressure two miles underwater, the bubbles remained locked inside the lava rocks. Once brought to the surface, however, where the pressure is a small fraction as much, the high-pressure gases in pockets near the surfaces of the rocks broke through explosively.

"It's kind of like the sound of ice cracking in water," said Dana Vukajlovich, describing the racket made by spontaneous explosions of the rocks when they were brought aboard the Roger Revelle research vessel in early October.

Unlike ice in water, however, the rocks were was as loud as firecrackers, she said. "You could hear it over the sound of the machinery on deck." There were even small pieces of the rocks flying off, she said.

And while all the noise is exciting, it's not what makes them so valuable to scientists, she said.

"They're pretty rare," said geochemist David Graham of Oregon State University of the few sites where popping rocks have been found worldwide. "They're typically found on relatively slow-spreading Mid-Atlantic Ridges."

That's an undersea rift zone where the crust of the Earth is being pulled in opposite directions and there are many volcanoes spewing out molten rock to fill the gap.

The rocks from what Vukajlovich's crew has dubbed the Krause Volcano are the only popping rocks found outside the Mid-Atlantic Ridge, said Graham.

What the popping rocks offer scientists is a chance to study volcanic gases that may have come undisturbed from deep in the Earth, said Graham.

While chemical analyses are just getting started on the Krause Volcano rocks, similar Atlantic popping rocks contained primarily carbon dioxide gas, said Graham.

Of more interest, however, are smaller amounts of argon and helium, both "noble gases" that do not chemically react with any other elements. Argon and helium are leftovers from the heat-producing nuclear decay of larger elements deep inside the planet, he said.

How much of each gas that's found in the rocks could support or challenge theories about how the interior of the Earth is heated.

"It helps in understanding the thermal budget of the Earth," said Graham.

And since argon tends to escape rocks more quickly than helium, the amounts of both in the Krause Volcano rocks will give a clue to how quickly the magma that made the rocks moved up from the Earth's mantle.

If, for instance, there's a lot of argon, it's more likely the rocks made a quick trip up. "We're hoping it's very well preserved gas from the mantle," Vukajlovich said.