AAC Publications - http://publications.americanalpineclub.org

Mt. Vinson, Scientific Studies

Mt. Vinson, Scientific Studies. In combination with the climbing and filming objectives of our expedition (see above), we undertook a glaciological study of snow accumulation in the Sentinel Range and also used a high-precision Global Positioning System (GPS) survey instrument to obtain the first accurate ground-based measurement of the summit elevation of Mt. Vinson. The snow accumulation study was intended to provide baseline information on the average amount of ice mass that is added to the east side of the Sentinel Range on a yearly basis. The GPS survey was intended to verify, or possibly bring into question, the currently established height of Mt. Vinson (4897m Above Mean Sea Level). (This is a fairly important distinction to make, because GPS coordinates are referenced to the Geodetic Geoid and not to sea level, as most maps are. Thus, one cannot compare GPS elevations to most map elevations without some correction. As I note later in the write-up, we adjusted our GPS elevations to correct for the different reference surfaces, so that our GPS measurements can be directly compared to the published map value.)

Although there have been numerous studies of mass balance throughout much of Antarctica, to our knowledge there have been no previous studies of snow accumulation (a key component of mass balance) within any of the mountain ranges on the continent. Furthermore, because our expedition started at the edge of the Rutford Ice Stream (ca. 200m) and ascended to the continent’s highest point (ca. 4900m), we were able to evaluate the variability in accumulation that occurs as a function of altitude for the most extreme elevation change within Antarctica.

Our accumulation study required digging several snow pits, which were two meters square on the surface and two meters deep, en route. The pits became more difficult to dig as we moved higher; with two people digging, they typically took anywhere from two to six hours to excavate. The lowest pit was at an elevation of 600 meters, and the highest one was at 3700 meters. In the pits, we mapped snow stratigraphy (layering), measured snow temperature and density, recorded snow hardness and crystal size, and collected snow samples for subsequent isotopic analyses. Preliminary interpretation of the data indicates that average annual accumulation nearly doubles between 600 meters elevation and 2400 meters, and then declines as one moves higher, presumably due to increased wind erosion (ablation) at higher elevations. The average annual layer thickness at 2400 meters was approximately 0.5 meter.

Our GPS survey of Mt. Vinson involved carrying to the summit the GPS receiver (about the size of a coffee can), a hand-held controller and data storage unit, a specialized lithium- battery power supply, and various connecting cables. Under optimal conditions, the GPS unit (a Trimble Model 4800) is capable of measuring its three-dimensional position with centimeter-level accuracy. Due to extreme cold (-35°F, not counting wind-chill), the visual display on the controller unit was nonfunctional when we reached the summit and attempted our first measurement. However, after warming it up inside our coats for about 20 minutes, it came back to life. This allowed us to collect two brief (about ten minutes each) sets of data, with the GPS receiver sitting on the highest point of rock at the summit of Mt. Vinson.

Upon returning from Antarctica, UNAVCO, in Boulder, Colorado, assisted us with processing the GPS data collected on the summit. The processing involved comparing our data with other GPS data collected simultaneously at the U.S. McMurdo and Palmer base stations. Results of our survey indicated that the summit of Mt. Vinson was at an elevation of 4901 meters, after adjustment to sea level, which is four meters higher than the currently published value of 4897 meters. However, given the large distances to the McMurdo and Palmer base stations and the relatively brief amount of time during which we were able to collect data on the summit, there is probably an uncertainty of a few meters in the accuracy of our survey results. Thus, our GPS measurements generally confirm the height of Mt. Vinson to be about 4900 meters.

Dan Stone, unaffiliated