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ICE THAT WON'T MELT / Discoveries in Menlo Park could lead to new natural gas source

Charles Petit, San Francisco Chronicle
Published 4:00 am, Tuesday, October 22, 1996
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Her ice would not melt, and Laura Stern, a government geophysicist in Menlo Park, could hardly believe it.

Her two more-experienced geophysics colleagues, Stephen Kirby, who

works with her at the U.S. Geological Survey, and William Durham of the Lawrence Livermore National Laboratory, tried to tell her to ignore it. Warm ice, they said, is a contradiction. It is called water.

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The granulated ice, after all, was sealed inside their laboratory apparatus. Maybe it was melting in there after all, and the instruments were just acting up.

But Stern did not ignore it. Even at 50 degrees Fahrenheit, the frozen water stayed solid for many minutes. Then, slowly, it was absorbed into another mineral without ever forming liquid.

As a result of her observation six years ago, the trio's flight of scientific curiosity about frozen, faraway moons took a U- turn detour right back to Earth and the discovery of baffling behavior by icy minerals abundant in oil and gas fields, but seldom studied closely.

"We did not know what to expect, but we found an unusual behavior at every single step of the investigation," said Stern, lead author of the team's report on the research, the cover story in a recent issue of the journal Science.

Not only have they found conditions under which seemingly ordinary water ice appears to stay solid at well above its normal melting point, they have found an ice -- although not pure water ice -- that gets stronger rather than weaker under high pressure.

To top it off, they learned a nifty parlor trick: how to draw fire from an icy, cold mineral that looks and feels like hardened snow.

"Here we go," she said to a visitor at the laboratory the other day, as she took a cold, white material from a freezer and broke it into a handful of lumps. It looked pretty much like water ice, except that it fizzed audibly, releasing flammable methane gas as it warmed up. "Sometimes it doesn't work right away," she muttered.

After a few moments' contact with a burning match, the material burst into a healthy blue and orange flame. It burned for about three minutes before flickering out. The icy mineral was reduced to a puddle of water.

The material is methane clathrate. It is a mineral in which molecules of methane, the most common component of natural gas, are trapped in a cage-like lattice of frozen water that has a somewhat different crystal structure than pure ice, but is technically a form of ice nonetheless.

Methane clathrate is the most common of a set of icy minerals called gas hydrates. It is stable only at high pressure and low temperatures. Oil industry workers know it well as an icy nuisance. It can form inside pipelines and clog

them in cold conditions. It also forms immense, natural underground deposits in arctic areas, as well as along continental margins in ocean sediment under a few hundred feet of water.

By some estimates, the amount of energy in methane clathrates and other such minerals could equal and perhaps significantly exceed that of all the oil, coal and conventional gas in the world.

Altogether, the scientists' recent discoveries may pay practical dividends. They could help unlock enormous new sources of natural gas that can be exploited for energy, reveal whether global warming will trigger massive and possibly catastrophic releases of natural gas from under the ocean, or determine the dangers of tidal waves from certain kinds of underwater landslides.

The mineral could also become unstable if global warming thaws methane clathrate-filled permafrost areas, releasing its methane to the atmosphere. Methane is a greenhouse gas that traps heat from the sun, and would act to accelerate global warming further.

The discoveries stem from a project Kirby and Durham began about 15 years ago. Impressed by images of the moons of Jupiter, Saturn and Neptune sent back by robot spacecraft, they decided to explore the behavior of icy materials that can dominate the crusts of worlds where temperatures fall hundreds of degrees below zero Fahrenheit.

"If it's cold enough, even water ice becomes just another rock," said Durham. "But the problem is, we had no good information on the behavior of ice under such cold conditions."

So the two began working their way through various kinds of ices, starting with pure water and moving on to a variety of geological slurpees -- frozen mixtures of water and other substances. Eventually, they got to methane clathrate, which could be common on Triton, a large moon of Neptune.

While known to occur naturally on Earth in cold, high-pressure underground and undersea environments, little was known about the mineral. Stern joined Kirby and Durham about 10 years ago. One of her tasks was to make pure samples of methane clathrate.

She filled a steel bottle with water ice, pulverized it into uniform grains about the size of table salt granules. Then she pumped in methane gas under high pressure to cause the ice to rearrange its crystal structure and trap methane molecules inside its cage-like lattice.

To speed up the process, she warmed the bottle above normal freezing. The ice was supposed to melt, briefly make water, then form the clathrate.

That is where the first surprise came. Pressure sensors on the bottle showed no telltale signs of the ice melting. At temperatures as high as 50 degrees Fahrenheit, it remained solid. Apparently, crusts of clathrate formed around each ice granule and prevented them from liquefying. Eventually, all the ice was converted to clathrate.

"When Laura first started to make this stuff and said the ice is not melting, we said, 'Nonsense,' " Durham remembers. "We told her to just keep cranking out the samples. You cannot superheat ice. It goes against everything we learned in school."

Durham has an idea of what is going on. Somehow, the methane prevents liquid water from forming, and without liquid water, "the ice has nothing to tell it that it is not supposed to be ice anymore."

There is no practical use, yet, for such "warm ice." But it could lead to new understandings of how a wide range of materials convert from solid to liquid, with unforeseen payoffs.

In the meantime, other experiments by the team revealed that methane clathrate becomes stronger under high pressure, while most ices tend to develop fractures and break.

That could be important not only for understanding the geology of frozen moons, but also the stability of the steep edges of continental shelves on Earth. Some researchers have feared that in undersea regions where it is common, methane clathrate can easily fracture, triggering undersea landslides that might cause tidal waves.

Keith Kvenvolden, a geological survey scientist who has studied clathrates for many years, said, "This new research may force us to think again whether this material is geologically stable."

The research might also help shape plans to explore methane clathrates as possible energy sources. Japanese government research agencies, for instance, say they will spend about $500 million in the next few years to find out whether methane clathrate deposits off their shores can be mined profitably.

The discoveries have forced Stern, Kirby and Durham temporarily to think about terrestrial applications of their research. But in the long run, they plan to keep their focus on comets, moons and other places where methane clathrates and other bizarre minerals are as common as granite is on Earth.