Denali Gets New Height along with Name Change

September 2, 2015  - By
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Two of the Survey climbers continue their trek up towards the next base camp, with gear in tow. Much of the climbing was done at night or early morning to take advantage of the frozen ground. (Photo: Blaine Horner, CompassData)

Two of the Survey climbers continue their trek up towards the next base camp, with gear in tow. Much of the climbing was done at night or early morning to take advantage of the frozen ground. (Photo: Blaine Horner, CompassData)

A new, official height for Denali has been measured at 20,310 feet, just 10 feet less than the previous elevation of 20,320 feet which was established using 1950’s era technology.

With this slightly lower elevation, has the tallest mountain in North America shrunk? No, but advances in technology to better measure the elevation at the surface of the Earth have resulted in a more accurate summit height of Alaska’s natural treasure.

The mountain — known as Mt. McKinley since 1917 — was officially renamed Denali this week, a change announced by President Obama on the eve of his trip to Alaska. Denali is an Alaska Native name meaning “The High One” or “The Great One,” and is the name Alaskan have used for decades.

“No place draws more public attention to its exact elevation than the highest peak of a continent. Knowing the height of Denali is precisely 20,310 feet has important value to earth scientists, geographers, airplane pilots, mountaineers and the general public. It is inspiring to think we can measure this magnificent peak with such accuracy,” said Suzette Kimball, USGS acting director. “This is a feeling everyone can share, whether you happen to be an armchair explorer or an experienced mountain climber.”

Blaine Horner of CompassData probing the snow pack at the highest point in North America along with setting up Global Position System equipment for precise summit elevation data. (Photo: Blaine Horner, CompassData)

Blaine Horner of CompassData probing the snow pack at the highest point in North America along with setting up Global Position System equipment for precise summit elevation data. (Photo: Blaine Horner, CompassData)

Denali National Park where the mountain is located, was established in 1917 and annually sees more than 500,000 visitors to the six million acres that now make up the park and preserve. About 1,200 mountaineers attempt to summit the mountain each year; typically about half are successful.

“Park rangers have been excited to work with and learn from their USGS colleagues using the latest technology to determine Denali’s height,” said Denali NP Superintendent Don Striker. “Climbers and other visitors will be fascinated by this process, and I hope our future park rangers see from this firsthand example how a background in science, technology, engineering and mathematics, and staying physically active in the outdoors can enable them to do some of America’s coolest jobs.”

To establish a more accurate summit height, the USGS partnered with NOAA’s National Geodetic Survey (NGS), Dewberry,  CompassData, (a subcontractor to Dewberry) and the University of Alaska, Fairbanks, to conduct a precise GPS measurement of a specific point at the mountain’s peak.

A previous 2013 Denali survey was called into question with an elevation measurement of 20,237 feet. That survey was done by an airborne radar measurement collected using an Interferometric Synthetic Aperture Radar (ifsar) sensor. Ifsar is an extremely effective tool for collecting map data in challenging areas such as Alaska, but it does not provide precise spot or point elevations, especially in very steep terrain.

The climbing team of GPS experts and mountaineers reached the Denali summit in mid-June. Since then, they have been processing, analyzing, and evaluating the raw data to arrive at the final number of 20, 310 feet. Unique circumstances and variables such as the depth of the snowpack and establishing the appropriate surface that coincides with mean sea level had to be taken into account before the new apex elevation could be determined.

Survey equipment was powered on. The Zephyr-2 GPS was connected to the NetR9 with Teflon tape on the threads. One of the primary concerns was that the position equipment would not power on in the cold temperatures. Each had been wrapped in closed cell foam to provide insulation and neither had any problem turning on. (Photo: Blaine Horner, CompassData)

Survey equipment was powered on. The Zephyr-2 GPS was connected to the NetR9 with Teflon tape on the threads. One of the primary concerns was that the position equipment would not power on in the cold temperatures. Each had been wrapped in closed cell foam to provide insulation and neither had any problem turning on. (Photo: Blaine Horner, CompassData)

The Summit Survey

The summit team arrived at the top of North America’s highest peak around 3:15 p.m. on June 24. Their first task was to identify the true summit. A small diamond of snow was prominent near the south-face cliff edge and was identified as the highest point of the mountain. A range pole was driven into the snow near the true summit, leveled with the summit, and GPS equipment was installed and powered on.

The team of two returned to 14,000 feet following the summit survey.  The equipment was left collecting until the following day when a team from Mountain Trip guiding service removed the receivers. Two days later the CompassData team returned to the summit and removed all remaining equipment.

The entire team safely descended the mountain and arrived at base camp at 7:00 a.m., June 29.

Processing the Data and Determining the New Elevation

To ensure the most accurate elevation number, specialists from CompassData, the University of Alaska Fairbanks and NOAA’s National Geodetic Survey all independently processed the survey data. Once they had preliminary results, a meeting was held to compare those calculations. All findings were consistent and remaining questions focused on how to express the new height.  Ultimately, an agreement was reached in terms of the reference surface to be used and the rationale for using the North American Vertical Datum of 1988 (NAVD 88) as the vertical datum.

NAVD 88 is the official vertical datum for Alaska in the National Spatial Reference System (NSRS), a system that is defined and maintained by NGS to provide a consistent coordinate system across the entire United States. A new effort underway at NGS to modernize the NSRS by 2022 will incorporate an improved model of where the average sea level, or ‘zero’ elevation, is located; this will result in elevation values being more accurate with respect to mean sea level.

A USGS feature story has more details about the trek, data collection and calculation methods.

A view of Denali from the airplane as the Survey team approached the Kahiltna Glacier to begin their ascent to the mountain’s summit. Photo : Blaine Horner, CompassData)

A view of Denali from the airplane as the Survey team approached the Kahiltna Glacier to begin their ascent to the mountain’s summit. Photo : Blaine Horner, CompassData)

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