Dust melts San Juans snow

Study says mountains denuded 30 days earlier

Bill Scanlon, Rocky Mountain News

Published June 26, 2007 at midnight

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Grandpa may have been right - there was more snow in his day, or at least it lasted longer.

A study by Colorado scientists shows that dust raised by farming, grazing, mining and recreation in the Four Corners area blew onto the San Juan Mountains and caused the snow to melt 30 days earlier this spring.

The study has implications for mountains from the Front Range to the Himalayas, said Tom Painter, lead investigator for the study done by the University of Colorado's National Snow and Ice Data Center.

It could mean less water for farming, shorter rafting and skiing seasons and less potential for hydroelectric energy. However, good management of reservoirs could lessen the negative consequences.

The wind-blown dust came from the Colorado Plateau, 200 miles southwest of the San Juan Mountains, which are in southwestern Colorado, said Painter, whose study appears in the current edition of Geophysical Research Letters.

"The amount of impact measured and modeled in this system stunned us," said Painter. "The fact that dust can reduce snow cover duration so much – a month earlier - transforms our understanding of mountain sensitivity to external forces."

The CU team measured snow at precise locations. They scraped the dust from some of the snow but left the dust on other samples. Then they compared results.

Global warming also may be playing a part in creating the conditions that send dust to the mountains in the spring, the CU researchers say.

The white snow reflects most of the sun's rays, said Stephanie Renfrow, of the CU center, who also worked on the paper. The dust-darkened snow absorbs more of the sun's energy, raising the temperature and melting the snow faster.

Prior to large-scale human settlement in the American Southwest, grasses held most of the dust in place, Painter said.

But after a century of breaking the desert crust, the dust blows freely, he said.

Painter talked to the Rocky by telephone from the base of Mont Blanc in France, which he said has its own coating of dust.

This summer, so does the Front Range, the Sawatch Range, the Gore Range and the Elk Range, he said.

It doesn't happen every year, he said. But while dust-covered mountains were a rarity 100 years ago, these days it happens every year when a drought combines with several sustained wind events, he said.

That's what happened in 2006 with eight big wind events in the Four Corners area, he said.

scanlon@RockyMountainNews.com or 303-442-8729

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