Glacial Changes Tied to Quakes

Retreating glaciers in southern Alaska may make earthquakes more likely there, according to a study by NASA and U.S. Geological Survey scientists in the July issue of the journal Global and Planetary Change.

The study reflects one of the under-appreciated consequences of global warming, said Jeanne Sauber, a geophysicist at NASA's Goddard Space Flight Center.

Glaciers in Alaska have shrunk "at least 10 percent in the last hundred years," because of higher temperatures and increased precipitation, she said. As they melt, they lighten the load on Earth's crust and allow the slowly drifting tectonic plates that make up the crust to move more freely. The collision of two plates under the Pacific Ocean off Alaska creates a buildup of pressure, which is relieved by earthquakes.

"This just makes it easier for earthquakes to occur," Sauber said. "This is equivalent to years of tectonic strain accumulating."

Sauber and co-author Bruce Molnia, a research geologist at the Geological Survey, used computer modeling as well as NASA satellite and global positioning system receivers to study movements of tectonic plates and shrinking glaciers over an area 150 miles long and 75 miles wide. They focused much of their attention on the Bering Glacier, the largest glacier in North America.

Although southern Alaska is not as populated as other U.S. areas, it is home to both the Alaska pipeline and the Kodiak rocket launch facility, Sauber said, adding that an earthquake in the region could cause tsunamis as far away as Hawaii.

-- Juliet Eilperin

Salmon Spawn Rainbow Trout

Scientists in Japan have engineered Asian salmon to produce the eggs and sperm of North American trout, an unprecedented bit of reproductive manipulation that may someday allow researchers to recruit common critters to replenish dwindling endangered species.

The team dissected newly hatched embryos of rainbow trout and removed small batches of "primordial germ cells." Those eventually become eggs or sperm in response to signals they receive from the developing fish.

The researchers, from the Tokyo University of Marine Science and Technology, injected those germ cells into newly hatched Pacific salmon embryos. Some of the cells made their way into the developing ovaries and testes of the recipient salmon, where they matured into rainbow trout eggs and sperm.

A year later, the team collected the milt -- the cloud of sperm that male fish release into the water at maturity -- of one of those salmon and mixed it with trout eggs. The result was a crop of purebred baby trout, sired by a salmon. (That salmon also produced salmon sperm, which when mixed with trout eggs created hybrid fish that did not survive.)

Other scientists have transplanted primordial germ cells from one fly species to another and from one bird species to another, resulting in the growth of sperm and eggs of one species inside the sex organs of the other. But the new experiment, described in the Aug. 5 issue of the journal Nature, marks the first such success in fish and the first to create progeny in any species.

Rainbow trout are plentiful, but the technique could help rare species. For example, salmon take one year to become sexually mature while trout take two, suggesting endangered species may be aided through reproduction by faster-breeding species.

-- Rick Weiss

More Young Men Using Viagra

Viagra is becoming increasingly popular among younger men, possibly in part because some are using it for purely recreational purposes, according to a new survey.

Express Scripts Inc., which monitors prescription drug use for the insurance industry, analyzed a representative sample of 5 million Viagra prescriptions between 1998 and 2002.

Overall, Viagra prescriptions increased 84 percent, the researchers found. While the majority of users are men in their fifties and sixties, the biggest increase occurred in younger men. Among those 18 to 45, the rate increased from three prescriptions per 1,000 men to nine per 1,000, according to a report published last week in the International Journal of Impotence Research.

Because the researchers found little evidence the men were taking other medications that would indicate they were suffering from erectile dysfunction, they suspect that at least some must be for purely recreational purposes.

"The conclusion one may draw is it's being used more for recreation and enhancement," said Thomas Delate, who led the study. "I'm not making a value judgment. I'm just saying this is what's happening."

Daniel Watts, spokesman for Pfizer Inc., the manufacturer, said the majority of users were clearly men with a medical problem.

"I think it's difficult to look at the study and know what the level of recreational use is. It's probably going on out there, but it's difficult to know how much," Watts said.

-- Rob Stein

The size of the red ring around each earthquake represents its magnitude.