The 400-mile-long Alaska Range, home to the highest point in North America, has largely been a mystery to geodesists. Despite running along a major fault, very little is known about how and where this massive area of land is moving.
Today, that’s all changing thanks to the USGS’s 3D Elevation Program, an initiative to map the Continental United States and Alaska, including marking and measuring the Alaska Range for the very first time. Once in place, these surveying points will provide a foundation for repeatable measurements to track the degree, rate and direction of movement over time.
Following the first official summit elevation measurement in over 40 years, a team of climbers from the USGS returned to Denali in the spring of 2016 to install a permanent Berntsen monument in the “Windy Corner,” a 13,400-feet point on the mountain’s West Buttress.
We talked to Blaine Horner, a lead climber on the project to learn more about the survey and the scientific value of this crucial first benchmark.
Capturing movement data for the first time
Until now, a number of Continuously Operating Reference Stations (CORS) around the mountain were the only means of gleaning any information into movement, however distance and geologic differences made these figures largely unreliable.
And while the 2015 summit survey was historic and informative, its position atop snow pack limited its value in terms of repeatable scientific data. This new survey monument, as Horner explains, is “the first repeatable point in the Alaska Range and in what will be a much larger data set in Alaska aimed at, essentially, building newer, better maps throughout the region.”
Matching the best location with the right survey tools
Since the project demanded permanent placement, a stable rock surface was needed to install the monument. With exposed flat bedrock, relatively low foot traffic, and regular sustained winds strong enough to keep the area clear of snow, the “Windy Corner” was the ideal place for installation.
In addition to finding a location somewhat out of the way, disruption to the mountain was also a concern. To minimize this, a brass survey marker from Berntsen was chosen as the permanent benchmark for both its low profile and robustness under harsh conditions. With previous painted markings made the year before wiped away from wind exposure, a metal monument was essential.
“Now that we have a heavy duty bronze marker there which won’t be blown away by the weather, we can survey the exact some place year after year.”
Using cordless hammer drills fitted with rock bits, a hole was drilled to fit the monument stem and a wider bit was used to ensure the cap was flush with the rock.
Using low-temperature epoxy, the monument was secured within the bedrock and a Trimble 5700 was placed on top of it to collect data over the course of seven days. Despite a period of bad weather, initial data collection was a success, giving researchers a baseline for future studies throughout the region as the newly official NGS monument was incorporated into its database.
The first step in a larger effort to track Alaskan plate movement
With the first of what will eventually be many markers around the Alaska Ridge, geodesists can finally begin tracking movement––down to the millimeter––around this important fault.
Moving forward, researchers plan to return the mountain in 2017 to collect data that can be compared to previous results, giving the greater research community the first ever extended time period survey in the Alaska Range.
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