Ocean Volcanoes : Deep- Sea...
About the only thing that frustrates geologist Rodey Batiza more than what he does not know about the ocean floor is what he does know about it.
The University of Hawaii volcanologist is at a loss to explain the various formations of lava where a deep-sea volcano erupted about 450 miles off Mexico’s Pacific coast 3 million years ago. Especially interesting to Batiza is the appearance of rock-like black glass amid the lava, which appears variously as ropy flows, pavement-like sheets and jumbled rocks.
At issue is the very nature of deep-sea volcanic eruptions, which spew the magma (hot lava) that continually replenishes the ocean floor as it spreads in tectonic plates toward the continents. Batiza is an authority on this volcano, named Seamount 6, which rises 4,950 feet off the ocean floor but, at its summit, is still more than a mile below the ocean’s surface.
Here is the enigma: the unusual black glass called hyaloclastite, tiny shards of crystal-free glass fused together and further cemented over time by sediment and manganese.
Batiza and other scientists generally believed that it was formed when the 2,000-degree Fahrenheit magma was explosively jettisoned into the ocean from below and mixed with the 35-degree Fahrenheit water, turning the magma into glass shards before it settled on the sea floor.
He published a science journal article on his hypothesis in 1989, espousing that deep-sea volcanoes erupted as fiery fountains. The hypothesis was well received and widely cited because it seemed the best explanation to date as to how the black glass was formed, Batiza said.
But he was troubled because the rocks at Seamount 6 contain virtually no bubbles to suggest that they were propelled by gases into the water when they erupted through the ocean floor.
Without that internal propulsion, and given the crushing pressure at that depth, how did the magma erupt into the water and mix quickly and freely enough with the water to create the glass?
The question may seem esoteric but reflects how little is known about ocean-floor geology.
“Four-fifths of the world’s volcanism occurs on the sea floor and we know practically nothing about it,” said Tom Simkin, a volcanologist and curator at the National Museum of Natural History at the Smithsonian Institution in Washington.
“Volcanism is an essential component of the growth and development of our planet, but there’s this huge gap in our knowledge and Rodey is doing a great deal to fill it.”
And so it was that Batiza, heading a team of 16 scientists, researchers and technicians and funded by the National Science Foundation, recently revisited Seamount 6 aboard Atlantis II, a research ship operated by the Woods Hole Oceanographic Institution.
The scientists observed the dead volcano by diving in the Navy’s three-person deep submergence vehicle Alvin, a mini-sub capable of diving to more than 14,700 feet and cruising along the ocean floor for several hours before its battery power is expended.
This set of six- to eight-hour dives took the scientists to depths of about 6,000 feet, onto the slopes of the undersea mountain.
The two-week expedition ended with as many new questions as answers, rendering undersea volcanism more mysterious then ever.
Moreover, what scientists found negated Batiza’s initial hypothesis. “That paper I wrote back in ‘89? I can throw it away,” he said.
Batiza and the others saw no evidence of a fountain volcano--the kind that is more common at shallower depths and led to the creation, for instance, of the Hawaiian Islands.
Another hypothesis--that the volcano was produced in a kind of giant belch where gasses blew plugs of magma out of the vent--also seems to have been disproved.
The researchers found no signs of lava splatter or--to use their unscientific nomenclature, cow plops--to suggest that magma was ejected into the water in wholesale fashion as balls of molten rock and plopped back to the sea floor.
Instead, Batiza’s group found greater evidence that Seamount 6, and perhaps other deep-sea volcanoes, was created when magma broke through the crust in dribs and drabs. In fact, the group could not even find any vent openings, suggesting that the vents became plugged with their own lava or sediment carried by the ocean current. Later eruptions surfaced through new vents, they believe.
Some of the lava observed by the group was in the shape of large, billowing pillows, suggesting that it oozed through a small vent and quickly solidified in place. Other lava deposits appeared as flowing pavement; still other lava appeared, inexplicably, just as jumbled, angular rock sitting atop the sediment of the ocean floor.
Most confounding to Batiza is one particular rock sample that was grabbed by Alvin’s mechanical arm on a dive when his wife, Jill Karsten, was in command of the day’s mission.
When Karsten showed the rock to the other scientists aboard Alvin’s mother ship, Atlantis II, knowing eyes widened with curiosity.
“It’s one of the most amazing samples I’ve ever seen,” Batiza said.
The rock was a piece of lava sheet flow, but paradoxically its upper crust contained a mix of lava and the black-glass hyaloclastite. “It told us this stuff is forming through a process we don’t understand at all,” Batiza said. “All we can guess is that the hyaloclastite was produced when the crust of the lava sheet flow was disrupted.”
Adding to the mystery, subsequent analysis of the sample at Batiza’s lab in Hawaii showed chunks of lava within the hyaloclastite. Why some of the magma turned into pedestrian lava and some into glass is unknown.
And whatever that answer, it would not explain why Batiza’s party found entire flows of virtually pure hyaloclastite. A ground-hugging lava flow wouldn’t seem prone to turning into glass shards because the molasses-like lava would not mix with water.
Batiza’s group will chemically analyze the 1,200 pounds of rocks, including hyaloclastite, that his team brought up with the Alvin sub. That study will show what the hyaloclastite has in common with the lava.
In addition, Batiza will view the hours of videotape shot from Alvin’s exterior cameras and pore over several thousand slides, taken both from the Alvin and a camera that was towed behind Atlantis II at night.
“I can tell you this: I am now genuinely confused,” Batiza said. “If we had come back with findings to substantiate our earlier hypothesis, that would have been gratifying--and, on the other hand, maybe a little boring too.
