Bishop's Ledge
[click to zoom]
© Wally Berg

Scientists Ponder Revision in Height
Members of the 1998 American Everest Expedition have come up with a surprising conclusion. After crunching some of the data collected while on the mountain, they now speculate the actual height of Mount Everest may need to be adjusted.

"The long accepted altitude of Mount Everest — 29,028 feet — may need to be adjusted..."
The current accepted height of 8,848 meters, or 29,028 feet, was arrived at in 1954 by an Indian Surveyor named B. L. Gulatee. Gulatee used the tools available to him at the time, including optical equipment (theodolite) which can be affected by atmospheric refraction, and spirit levels, which can actually be affected by the gravitational pull of the mountains themselves. The 1998 American Everest Expedition used GPS equipment, which is not subject to distortion caused by those phenomena.

The expedition, sponsored by Boston's Museum of Science and partially by The National Geographic Society, was wholly oriented to making scientific measurements on the mountain. When expedition leader Wally Berg reached the summit on May 20, one of his primary mandates from the scientists was to mount a GPS receiver firmly in the highest solid bedrock on the summit. That point is the Barry Bishop Ledge, so named because it is the same rock outcrop visible in the famous 1963 photograph of Lute Jerstad taken by Barry Bishop near the summit, with the American flag visible. For several years this outcrop was referred to as Barry Bishop Rock, but at the suggestions of the Museum of Science's Brad Washburn, the name has been revised to Barry Bishop Ledge to more accurately reflect its nature.

"Running a GPS receiver on the actual summit itself was not high on our list..."
During his two hours of work on or near the summit, Wally Berg was able to laboriously drill two holes in Barry Bishop Ledge, place two bolts, establish a benchmark and fix a Trimble 4800 GPS receiver in place. Wally then turned on the receiver, which began collecting data. The device, along with its data, was retrieved by other climbers approximately a week later.

The Trimble GPS
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© Wally Berg
Charles Corfield, of Palo Alto, California, who was science manager for the 1998 American Everest Expedition, and Dave Mencin, of Boulder, Colorado, who was the chief on-location scientist for the expedition, have now reviewed the data with other scientists. They have reached the conclusion that the long-accepted altitude of Mount Everest — 29,028 feet — may need to be adjusted downward, although not so much as to threaten the mountain's status as the highest on earth.

In fact, one result of their scientific studies last spring was to come away impressed by the work of their 1950's Indian counterparts. "You have to be impressed," said Mencin, "that with all our satellite measuring systems and other advantages, our numbers are still within 10 meters of Gulatee's 1954 survey."

"It's a classic work," concurs Corfield, "and sets a high standard to follow."

"Everest remains the tallest mountain by a wide margin..."
Corfield described to The Mountain Zone how the measurements were conducted: "Last spring, our priority was to establish and occupy a benchmark on the Bishop Ledge. Running a GPS receiver on the actual summit itself was not high on our list — the summit is made of snow and is therefore a moving target due to seasonal accumulation and ablation of the summit snowpack.

"However, the height we have measured for the Bishop Ledge suggests that the official height of the mountain itself may well need to be revisited.

"Our figures from this spring, which I will round to the nearest 10m for simplicity, are as follows: after corrections for geoid (see editor's note below) Bishop Ledge was measured at 8,810 meters.

Everest from the north
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© Art Wolfe
Now our best guess is that the summit lies no higher than 20 meters above the ledge, and probably no more than 15 meters — give or take changes in snowpack. Therefore, the contemporary height for the summit would be no more than 8,830 meters, which is a hair less than 29,000', or about 30 feet lower than the current accepted height of Mount Everest."

Dave Mencin added, "The thing I think we need to point out is that the largest probable error in these computations is our 'guess' at the vertical separation between Bishop Ledge and the snow summit."

Even so, both scientists think that some revision in the altitude of Mount Everest is required, but not necessarily to any significant effect. "To dispel any doubts," cautioned Corfield, "Everest remains the tallest mountain by a wide margin. K2, the second highest mountain in the world, has been measured at 28,250 feet."

But a new "official" height of Mount Everest might in fact mean that no mountain on earth is higher than 29,000 feet.

Peter Potterfield, Mountain Zone Staff

Editor's Note: Readers should understand that modern surveyors use geoid and ellipsoid models to measure high mountains. Those are complicated concepts, but the technically inclined should [click here for Dave Mencin's and Charles Corfield's explanation] of these models, and on the methodology of last spring's measurements.

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