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Time to recalibrate elevation of peaks

JACKSON, Wyo. — It's time to recalibrate. Grand Teton is not 13,700 feet after all, as many locals can readily recite. It's actually five feet taller.

How so? Angus M. Thuermer Jr., the long-time managing editor of the Jackson Hole News&Guide, talked to surveyors, GIS experts and cartographers to explain why something so precise measured in feet and inches is, actually, somewhat difficult to measure. It mostly has to do with sea level.

The Teton Range has continued to rise since the Hayden Survey first surveyed the peaks in 1872, perhaps 5½ inches. And measurements from the valley floor are accurate. What's changed is a new understanding of sea level.

Steve Reiter, with the U.S. Geological Survey in Lakewood, Colo., explained that what has changed in the last century is an understanding of what gravity does to sea level.

"Gravity is unevenly distributed over the globe. Where strong, it's going to pull that ocean down in a valley."

If you were on the Pacific Ocean on a perfectly calm day, for example, "that ocean surface (would have) hills and valleys on the order of 10 feet," he said.

Gravity is affected by mass, and areas beneath mountains tend to have a lot of it.

This means that with all this mass of mountains in Wyoming, there is stronger gravity. Bob Smith, a geophysicist and a professor at the University of Utah, explained that you should think of a canal of water that crossed North America. This water-filled canal would be five feet lower as it passed under the Grand Teton than it would at the Atlantic or Pacific.

"Sea level would be different at Jackson Hole than in Denver or Boise."

This new understanding also means other peaks in the Teton Range aren't quite the height everybody thought they were. Hundreds of them go only by their elevation, as in the case with Peak 9,974 feet. Properly, It's now Peak 9,980 feet.

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