Sentinel Range, overview. In the 2001-02 season 67 climbers, including only four women, attempted Vinson by the normal route. Sixty reached the summit, producing a success rate of 90 percent, slightly lower than usual. No new routes were climbed in the range during the season, though the experienced Antarctic guide Dave Hahn, guiding a geological excursion, summited a number of minor points in the Marble Hills area.

There was only one expedition attempting anything other than an ascent of Vinson Massif by the standard route. The Omega Shinn GPS Expedition proposed to take an accurate GPS height reading of the summit of Mt. Shinn. In 1998, when I wrote The Antarctic Mountaineering Chronology, a reference book on ascents made in Antarctica, I realized there was no single, accurate, and accepted figure for the altitude of Mt. Shinn, supposedly the third highest peak in Antarctica. The figures given in various publications range from 4800m down to 4650m. The latter would make it the same height as Mt. Craddock, supposedly Antarctica’s fourth highest peak.

The original surveys of the high Sentinel peaks in the early 1960s put Vinson Massif at 5140m, later changed to 4987m after a resurvey in 1979 and the republishing of the USGS topographical map to the area in 1988. The second highest peak, Mt. Tyree, was reduced to 4852m, but no new figure was given for Mt. Shinn.

The USGS publication Geographic Names of the Antarctic, by F.G Alberts (2nd ed. 1995) gives no numeric height for Shinn, but says, “A mountain over 4,800m….” The USGS

Geographie Names Information System website has no numeric figure for Mt. Shinn, similarly stating: “A mountain over 4800m….” The 1988 USGS topo of the area, Vinson Massif, has no numeric altitude figure on Mt. Shinn, as it does for most of the high peaks. The June 1967 issue of National Geographic features Nick Clinch’s expedition that made the first ascents of Vinson, Tyree, Shinn, Gardner, and others. It puts Shinn at 15,750' (ca 4802m) but those figures were taken on the original 1960s surveys, since amended.

I felt that Shinn was probably lower than 4800m, though higher than 4600m. The Omega Foundation, an organization that supports science in the polar regions, agreed to an expedition that had as its primary aim a new, accurate GPS reading taken on the summit of Mt. Shinn. I was joined by Mike Roberts, a professional guide from New Zealand with 11 previous Antarctic expeditions to his credit.

We procured a Trimble 5700 Total Station GPS receiver, the successor to the 4800 model used by Washburn’s team on Everest in 1998 and a NOVA crew the previous year on Vinson— who recorded Vinson at 4901m. The plan was to climb Shinn by the normal route, measure it, climb Vinson Massif, then sled 45 kilometers north to attempt the first ascent of Mt. Anderson (4157m), the highest unclimbed mountain in the Sentinel Range. To gather enough accurate data, a recording session of at least six hours on the summit of Shinn was deemed to be necessary. Data would be downloaded through the website of the Australian Land Information Group (AUSLIG) to give an Above-Geoid figure (GPS figure), and then post-processing by AUSLIG would produce a figure comparable to traditionally surveyed Above Sea Level figures.

The expedition’s November 16 start was delayed by two weeks due to the failure of Adventure Network International to procure sufficient aircraft to begin operations for the season. The expedition landed on the ice at Patriot Hills on November 30 and reached Vinson Base Camp the next afternoon by a combination of DC3 and Cessna flights. We started up the lower Branscombe Glacier within hours of landing, stopping at the usual Camp 1 site that evening and proceeding to the usual Camp 2 the next day. After four days of storm we made a route through the seracs at the top of the headwall beneath the Shinn-Vinson Col and established Camp 3 in the usual position. After deciding that more acclimatization was needed for our summit stay on Shinn, a partial ascent of Vinson’s normal route was planned for the next day. In good weather, progress was slow, but we decided to continue to the summit and with two Norwegians made the first summit of the season. Upon return to Camp 3, other teams had arrived and planned to summit the next day. However two days of very bad weather with high winds, low visibility, and some snowfall followed, necessitating regular forays outside to dig tents out of severe drifts.

December 10, the 11th day on the mountain, dawned beautifully clear with only a light wind, so we set off in down suits for Shinn at 9:45 a.m. with the GPS unit and a small summit tent for the Shinn summit data session. At 2:30 p.m. we were around 100 meters below the summit on the southwest face when we encountered severe windslab avalanche conditions, a result of the previous two days’ storm emanating from the northeast. Attempts at traversing around this area proved fruitless and we were forced to descend.

At Camp 3 Roberts learned of a medical emergency in his family that necessitated his return to the United States immediately, so we descended to Vinson Base Camp on December 11. Most parties were now ready to leave for home. I endeavored to find help to complete the Omega project on Shinn but though a guide was very willing to do so and Omega offered to fully cover his changeover and insurance costs, ANI would not allow him to stay.

The failure to accurately measure Shinn was particularly disappointing given the observations made with wrist altimeters on Vinson and Shinn. On Vinson (4897m or 4901m) our altimeters (mutually calibrated at previous known points) read 5130m—roughly 230 meters “high.” At their high point on Shinn—estimated to be 100 meters below the summit— my altimeter read 4750m. If one subtracts the same discrepancy from this as found on Vinson—i.e. 230 meters—one could estimate our “real” high point as 4520m. If our estimate of distance below the summit is correct, then Mt. Shinn is only 4620m. Even if allowances are made with the altimeter readings and our judgement of distance to the summit, Shinn is still substantially lower than 4800m and possibly lower than 4700m. It is evident that significant work of this nature still needs to be done in this area.

Damien Gildea, AAC, Australia