The First Laser Measurements to the Summit of Mount McKinley
DURING the early summer of 1977 Boston’s Museum of Science planned to complete a two-year project of making a very precise map of Muldrow Glacier, which flows off the northeast flank of Mount McKinley in Alaska. This glacier has a history of extraordinary surges—one around 1912, another in 1956-7—after each of which the ice mass shrank dramatically, after a brief period of incredible crevassing and disruption. The ice-surface dropped nearly 300 vertical feet in the McGonagall Pass area after the surge of 1956-7.
Although a number of other glaciers have exhibited the same behavior, Muldrow is one which is not only easy of access, but is visited ever more frequently by climbing parties, and the Museum of Science felt that an extremely detailed map of the Muldrow valley would be of ever-increasing interest as the years went by. It is also hoped that, with a fine, large-scale map made in Switzerland1 (scale 1:10,000 with 5-meter contours) groups of younger scientists might become interested in making serious studies of the geology, glaciology and botany of the area which could reveal more facts about this fascinating part of Alaska.
In order to do the field-work in June and July 1977, Keuffel & Esser loaned one of its extraordinary new Rangemaster II laser-measuring instruments to the Museum, and immediately I had the thought that it would be interesting to use it to do another survey job in the area that could not be accomplished without this powerful new sort of distance-measuring equipment. Accordingly I asked NOLS (National Outdoor Leadership School) if they would be willing to carry an array of our laser prisms to the top of Mount McKinley so that, while we were in the Park at the same time, we could make a very, precise measurement of the position of the South Peak.
Twenty years ago the geographical position of McKinley’s two peaks was determined by lengthy computation of the U.S. Coast-Geodetic survey, using field observations by their field parties of 1952 and 1953, our parties of 1947, 1951 and 1953 and a number of similar observations made by the U. S. Geological survey. A score of sights, all intersecting on the South Peak, resulted in a new, precise, official altitude announced in 19562 of 20,320 feet and latitude 63° 04' 10.509" and longitude 151° 00' 15.298".
However, this position arose from a mathematical solution of a complex series of “triangles of error” in the summit area, as these theodolite sights were from many different distances and directions and they did not by any means all intersect precisely in one neat spot. Although we have all been relatively sure that the mathematical position is very close to the real position, our work with NOLS helped to zero in on the real spot.
We delivered 33 prisms, weighing 36 pounds to Q. Belk’s 20-man party at its 6400-foot camp just below Muldrow’s lower icefall on June 20 by helicopter, after we had finished using them in our work along the lower course of the glacier. We also loaned NOLS a very light and reliable radio (General Electric “Personal Portable” model PE), with which we could be in constant communication with them and the National Park Service Eielson Visitor Center during their climb.
On July 10, after a long period of unsettled weather, the first really clear period in nearly a month started to shape up. The NOLS party was at its high camp (16,400 feet) at the crest of the lower icefall of Harper Glacier and we were at Camp Denali 32 miles to the north, in the lowlands near the end of the McKinley Park road. Early that morning we drove over to the highly precise survey station at the Eielson Visitor Center, set up by us for this purpose in 1949. NOLS had divided its party into 2 groups—one to make the climb on July 11, and, weather permitting, the other on the 12th.
The weather on the 11th was incredible—hot, calm and almost cloudless. We followed the party in its ascent with periodic radio chats at hourly intervals during the day—all of us wondering whether it could possibly remain totally clear for twelve consecutive hours! It did, but this created an unanticipated problem: the heat in the lowlands (92° at Eielson!) developed a pall of blue haze so thick that, when Brian MacLean’s party reached the top at 3:30 P.M., although we could see the summit clearly, our laser beam was not powerful enough to get to the summit, bounce off our reflectors and get back to us after the 66-mile round-trip with sufficient power to activate our instrument.
It was infinitely frustrating. We could clearly see the ruby ball of light at our reflectors, carefully assembled and set up by NOLS on the summit, but our instrument refused to react.
On the spot, by radio, we made a speedy decision: to leave the array of prisms, lashed to an ice axe, on the summit for the night and to have them picked up and brought down by Q. Belk’s second NOLS party on July 12. We reasoned that by late in the evening it would cool off, the haze would dissipate and we could succeed in making our sights. We were a bit scared at leaving $5000-worth of optical glass on the summit of the South Peak, for if the weather went sour the prisms might stay there a long, long time!—but the weather looked really solid and we were confident that this was a safe gamble.
It was. After supper, at nine o’clock that night, we returned to our instrument at Eielson to find that park ranger Karl Semmes had already turned it on, aimed it, and was receiving a good return signal. The next hour was very thrilling to all of the little group gathered around the Rangemaster and its operators. The sun had set in the valley, but a gorgeous twilight glow still bathed McKinley’s twin summits, giving them the subtle, unearthly, detached appearance which always makes this view on a clear evening a never-to-be-forgotten experience—and, right atop the South Peak, the intensely-brilliant ruby ball of laser-light throbbed and pulsated on and off, on and off, for nearly an hour, as we made sight after sight, each with a different setting of the instrument in order to secure the most accurate result.
Our one technical problem was the fact that, with nobody actually at our reflectors, we did not know the exact temperature and barometric pressure at the upper end of our line. We had to be satisfied with a computation of the difference in pressure and an estimate of the temperature, based partly on experience, partly on the true temperature that night at NOLS’ 16,400-foot camp and partly on the free-air temperature secured from balloon-runs above Anchorage and Fairbanks that night.
The results were exciting. The true laser distance from Eielson to the summit, when finally computed by the Coast Survey from our figures, was 175,852.91 feet compared with the calculated distance of 175,834.54 feet to the spot where observations of 25 years ago had pinpointed it— placing the summit only 18.37 feet southwest of where it was thought to be!
The next day dawned superbly clear again, but by the time that the second NOLS party (led by Q. Belk today) had reached the summit at 4:30 P.M., they were completely cut off from the lower world by a vast sea of clouds that stretched to the northern horizon below them. We had hoped, if the weather had held, to be able to make another laser sight to the top from another survey station almost exactly north of the mountain, and thus check its true latitude (the sights of the 11th having nailed down the longitude)—but that would have been too good to be true. Maybe, if NOLS is willing to carry some more prisms to the top another year and we can borrow another Rangemaster from Keuffel & Esser, we can do this at a later time. It’s an unforgetable experience to climb McKinley, but always much more rewarding and interesting if one can also accomplish something worthwhile of a scientific nature at the same time.
The second NOLS party didn’t just pick up our prisms and carry them back to camp on July 12. We had given them a sketch-map of the summit area and a 200-foot plastic tape with which they made a number of careful measurements around the top which will be very useful for climbing parties in the future—and which also revealed some exciting historical details of the Parker-Browne-La Voy near-ascent of June 29, 1912.
When I climbed the South Peak as a member of the U. S. Army party in 1942, I made a picture looking northeastward from the top on a beautifully clear July afternoon. Belmore Browne, an old friend of many years, had told me exactly where he, Merl La Voy and Professor Parker had been forced to give up their attempt in a violent southwest windstorm. I photographed Terris Moore and Bob Bates exactly where Browne told me he gave up, after crawling on his hands and knees as far as his exhausted muscles would allow him to go, after Prof. Parker and La Voy had given up at the tip of the summit’s northeast shoulder, now known as Carter Horn. NOLS measured to the exact spot where Parker and La Voy had stopped—990 feet from the summit and only about 125 vertical feet below it—and also to the exact spot where Browne gave up —330 feet on his hands and knees and only 660 feet from the top, measured along the slope!
Browne told me how he could never erase from his mind the vision of the final drifts of McKinley, occasionally torn free of the clouds by the southwest tempest, then lost again in an inferno of mist and blowing snow. Climbers have always wondered why he never could make those last few yards—a stroll of a dozen minutes on a clear afternoon—nobody knows the answer to that query but a handful of us who have lived and worked for weeks on the upper slopes of McKinley, whose blizzards and gales defy description to anyone who has not been there himself.
We are very grateful to NOLS for their careful and accurate work which has helped us to reveal still more interesting facts about the crest of North America.
1In collaboration with the Swiss Foundation for Alpine Research and Swissair Photo Vermessungen, both of Zürich.
2The Military Engineer, Sept.-Oct. 1956, page 384.