Science/Medicine : Recipe for an Undersea Isle
‘The slow constant seepage of molten rock was not violently dramatic. Layer upon layer of the earth’s vital core would creep out, hiss horribly at the cold sea water, then slide down the sides of the little mountains that were forming.’
James A. Michener, “Hawaii”
Off the Hawaiian Islands, scientists are getting one of their closest views yet of the earth 3.5 billion years ago, a time when volcanoes dominated the planet. Researchers hope to find clues about the origins of life, and the chemistry of geologic upheaval.
Three thousand feet beneath the sea, another little mountain is forming.
No sign of it yet appears on the surface, but scientists predict the burgeoning seamount known as Loihi will emerge as the next Hawaiian island--sometime in the next 100 to 10,000 years.
So don’t make any trip reservations yet, even though the simmering volcano is already drawing visitors--marine geologists, chemists and biologists.
Loihi rises 13,000 feet from the floor of the north-central Pacific. It intrigues scientists because it is believed to provide a pipeline extending deep into the mantle, the section of the Earth between the crust and the heavy metal core.
Even though the Hawaiian Islands are relatively recent additions to the landscape, Loihi is offering scientists one of their closest views yet of the Earth 3.5 billion years ago--when volcanoes dominated the planet. The first fossils date back about that far.
By studying it, scientists hope to find new clues about the origins of life on Earth. Already, they have been surprised by some of what they have seen around the undersea volcano. The rare opportunity to study such a growing mountain also is serving to confirm the validity of some long-held theories.
Scientists from the University of Hawaii returned in September from a voyage to Loihi aboard the mini-submarine Pisces V, owned by the Hawaii Undersea Research Laboratory. The dives found further evidence that Loihi is growing to the south, an observation consistent with the notion that the Hawaiian Islands were formed over the last 40 million years by a relatively stationary volcanic “hot spot” deep within the Earth.
Accepted as scientific gospel today, the hot-spot theory and the larger arena of plate tectonics were not mainstream science when James A. Michener wrote his best-selling 1959 novel, “Hawaii.” So he can be forgiven for describing the islands as growing up along a long rupture, rather than from a single volcanic source.
Harmon Craig of Scripps Institution of Oceanography in San Diego has used heavy helium as a chemical tracer to show that Loihi taps gases from the Earth’s lower mantle, 400 to 1,800 miles down.
“The lower mantle is the last great area of exploration left on Earth, after Antarctica,” said Craig, chief scientist on the first dives to Loihi, aboard the submersible Alvin in February.
The only clues to this mysterious realm come from seismic echoes, magnetic field measurements, and a few volcanoes that, like Loihi, are believed to have their sources in the deep mantle. Most volcanoes, including Mt. St. Helens in Washington--associated with the Pacific’s “Ring of Fire”--have sprouted from near where the Earth’s plates are forming or colliding.
Chemicals from the lower mantle are thought to be pristine clues to the ancient ocean and atmosphere from which life grew.
For instance, unlike continental volcanoes and Hawaii’s above-ground volcanoes, Kilauea and Mauna Loa, Loihi emits methane, a volatile gas that also occurs through the breakdown of organic material.
That, Craig said, lends support to the argument, first put forward by University of Chicago researchers Stanley Miller and Harold Urey in the early 1950s, that--before life existed on Earth--lightning in a methane-rich atmosphere produced amino acids and nucleotides, organic compounds necessary to life.
More recently, Joel Levine, an atmospheric chemist with NASA, argued that methane would break down too quickly in the ancient atmosphere to form organic compounds. He suggested that steam, carbon dioxide and nitrogen--the main emissions from volcanoes--were the key life-producing compounds, and other research has used them to reproduce the Miller-Urey results.
The debate over the pre-biotic atmosphere remains one of the hottest in science.
Loihi--Hawaiian for “long,” after its oval contours--lies 28 miles east of Hawaii’s South Point, the southernmost point in the United States. Discovered in the 1950s, it was originally believed to be an inactive seamount like those around Hawaii formed with the sea floor.
But seismic tremors soon told scientists that Loihi had a volcanic life of its own, independent of the other Hawaiian volcanoes.
It is now recognized to be the youngest example of a 65-million-year-old geologic process. Comparable to an outer skin or the shell of an egg, the Earth’s Pacific crust over the eons has been slowly sliding over partly molten rock in the mantle.
As the plate moved--and continues to creep--toward the Aleutians and Japan, the plume of magma melted right through the crust and created islands. Once away from the volcanic source, the islands slowly shrank, eventually becoming coral atolls, then shallow guyots, and finally sunken seamounts.
As one of possibly only three active hot-spot submarine volcanoes, Loihi serves as a natural hypodermic needle penetrating the Earth’s skin and drawing out minerals and gases.
(The other two submarine volcanoes are in French Polynesia. Only in October, one of them, the MacDonald Seamount, erupted beneath a research vessel, enveloping it in a swirl of murky water, gas bubbles and hot volcanic rocks. A third may be Mehetia, about 90 miles east of Tahiti.)
To Earth scientists, Loihi’s chemistry is as interesting as blood gases are to a doctor. To a geologist, its rhythms are the birth pangs of an island.
In recent years, scientists have charted its terrain by sonar and underwater photography, measured its magnetic field and dropped lines for rock and water samples. In 1982, instruments heard a deep seismic heartbeat between Loihi and its elder siblings, Kilauea and Mauna Loa, suggesting a common pool of magma at a depth of 37 miles.
This year’s expeditions were the first in mini-submarines. The fruits of the scientists’ labor still have not been fully digested.
One intriguing discovery was a rare and ugly species of angler fish. At first it was believed to be a new species, but Scripps fish expert Richard Rosenblatt later identified it as Sladenia remiger , a member of the angler order and monkfish family found only once before, in 1912 in the Philippines.
Instead of the coral, fish and other creatures found on seamounts nearby in the Pacific, the scientists found on Loihi a barren moonscape, a volcanic rubble heap. Only the angler fish and a previously unknown form of bacterial life occupied the summit.
The Alvin, owned by the Navy and operated by Woods Hole Oceanographic Institution in Massachusetts, in February measured Loihi’s shimmering fields of volcanically heated water at a balmy 87 degrees Fahrenheit, compared to 40 degrees for the ambient sea.
The researchers also collected rocks so saturated with carbon dioxide that they popped and fizzed like champagne when brought to the surface.
The water also had a surprisingly high concentration of carbon dioxide. Loihi’s summit is in essence a soda fountain.
The froth, nicknamed Pele’s Champagne after the Hawaiian volcano goddess, was found to hold 4,000 times as much free carbon dioxide as normal seawater. That’s 140 times higher than seawater’s total carbon dioxide content and 40% more carbon dioxide than the African lake that in August, 1986, released enough gas to asphyxiate 1,500 people.
“I’m excited about it because it’s telling us what’s coming out of the mantle,” Craig said. “Carbon dioxide is the primary carrier gas that brings volatiles out of the mantle.”
“The vent fields are on the sides of very steep pinnacles,” said Alexander Malahoff, director of the Hawaii Undersea Research Laboratory. “The most active part is the southern rift, so the volcano is growing south.”
Nowhere to be seen were the hot vents or weird colonies of sulfur-eating organisms found near plate ridge boundaries in the eastern Pacific. Instead, the Alvin and later the Pisces V brought back oxides of iron and other metals.
These metals are of interest to marine geologists and chemists because they are thought to be part of a water-borne metal recycling system.
Only in the last 10 or 20 years have scientists realized that the interior of the Earth is part of that recycling system, along with the atmosphere and oceans. The water cycle taught to schoolchildren for decades--clouds, rain, rivers, oceans and evaporation--has been expanded to include the planet’s interior.
Scientists estimate the Earth’s entire water supply passes through the crust every 8 million to 10 million years. Nearly all of this exchange occurs at or near boundaries in the Earth’s plates, such as the East Pacific Rise, the pushy southern neighbor of California’s San Andreas Fault. At plate boundaries, water percolates down through the porous crust, heats up near the magma source, then escapes back to the sea, sometimes in the form of breathtaking “black smokers”--chimneys of water hot enough to melt lead.
Since Loihi’s vents are merely warm, the percolation process at submarine volcanoes now is believed to be faster than at sea floor spreading centers. The water at Loihi has less time to get hot at the magma source, scientists suggested.
Studying the chemistry of warm- and hot-water vents gives scientists an idea of the Earth’s natural cleansing processes. Examining mineral deposits also helps geologists assess the potential for sea floor and seamount mining.
After their first look at Loihi, several scientists made observations that were poetic as well as empirical.
“Birth is painful,” Hawaii biologist Richard Grigg wrote during an early dive. “Laboring to reach the surface, heaving under 100 atmospheres of pressure from overlying water, and with streams of hot water gently pouring out, the volcano is perhaps building up for the next good blow, when pillows (of lava) will pile into massive rock mounds, fracture, and collapse into undersea avalanches rumbling downslope.”
Not bad. But Michener should have been there.
WHAT SCIENTISTS FOUND AT LOIHI
Heat vents, above: Water emerging from volcanic heat vents--white staining occurs around the vents--was cooler than anticipated, fueling speculation about the depth of Loihi’s volcanic roots and explaining something of how the Earth’s natural cleansing processes work. The volcanically heated water shimmered at about 87 degrees Fahrenheit, as compared to about 40 degrees for the surrounding seawater. But that was less warm than had been expected.
Volcanology: Unlike many better known volcanoes, including Mt. St. Helens, which sprout from near where the Earth’s plates are forming or colliding, Loihi’s roots reach into the deep mantle beneath the Earth’s crust. Chemicals from the mantle are thought to be pristine clues to ancient ocean and atmosphere conditions.
Biology: The undersea area is devoid of anticipated animal life. Scientists did find what they at first believed a new species of fish. Later it was identified as a rare angler fish, of the monkfish family. Only the angler fish and a previously unknown form of bacterial life occupied the summit.
Geology: Water and rocks from the area were so saturated with carbon dioxide that they popped and fizzed like champagne when brought to the surface. The summit is, in essence, a soda fountain. Scientists concluded that the carbon dioxide is a primary carrier gas to bring substances out of the Earth’s mantle.
