Glacial Movement in the Khumbu Icefall
SINCE 1921 WHEN GEORGE MALLORY FIRST SAW IT from the brink of the Lho La, Everest’s Khumbu Icefall has been viewed with great respect—and, indeed, with considerable awe. It plunges for slightly over 2000 feet in only a mile from the lower end of Everest’s Western Cwm to the nearly level Base Camp area of the Khumbu Glacier at the foot of magnificent Pumori. In particular, the upper third of this icefall is a spectacular cascade of giant crevasses, tottering séracs and shattered blocks of ice—the sort of features that are always related to fast-moving glaciers. All sorts of “guesstimates” have been made over the years as to how fast this ice-Niagara is moving. Yet we are unaware of any scientific record of this rate.
So, in the spring of 1994, a small trek was fielded by the Central Department of Geology of Kathmandu’s Tribhuvan University and Boston’s Museum of Science to make a series of preliminary measurements to determine whether a longer and more detailed study of the icefall’s movement would be worthwhile.
The members of this party were Dr. Prakash C. Adhirkary of Tribhuvan’s Geology Department, Adams Carter and myself, with able support from Sirdar Tshering Lhakpa Sherpa and five other porters. We were also helped by Tribhuvan’s Dr. B.N. Upreti and by surveyor Buddhi Shrestha. Before reaching Base Camp, we received assistence with our electrical equipment from Gian Pietro Verza of the Italian High Altitude Research Project Pyramid at Lobuche.
The technical equipment used was a Wild T-3 theodolite and a light-weight Keuffel & Esser Uniranger, an infra-red electronic distance-measuring instrument, which yields motion readings in both millimeters and feet up to a distance of eight kilometers (five miles). The positioning of this equipment in the field was based on the National Geographic/Boston Museum of Science large-scale map of the area, as well as large-scale prints of the vertical aerial photographs from which this map was made.
We flew from Kathmandu to Lukla on April 23 and proceeded on foot along the well-worn trail to the Everest Base Camp area via Namche, Thyangboche and Pheriche. We arrived at Base Camp on May 3. A brief reconnaissance located an excellent level observing site atop a very high abandoned lateral moraine of the Khumbu Icefall at the foot of the steep slope which rises to the snow collar of the Lho La. This spot was reached by a short, very steep climb up a treadmill of morainic gravel, a few hundred meters north of the Base Camp area. The climb up was always made at dawn while the boulders and rocks were still held fast frozen to the slope. Descent in the late afternoon was made with one’s fingers crossed. The vertical angles observed from here to the fast-moving upper part of the icefall were only slightly more than 12°—thus resulting in negligible correction of the observed distances.
We were helped enormously by members of two expeditions which, at this time, were in the midst of ascents of Mount Everest: Alpine Ascents International and the Everest Environmental Expedition. The prisms required to determine the rate of motion were set at three different locations beside the climbing route through the icefall. Frequent readjustments were made by the climbing personnel to maintain proper positioning for the measurements. Special thanks are due to Pete Athans, who set the prisms in the icefall and saw to it that they were not disturbed during the actual hours of observation on May 4, 5 and 6.
The lowest and highest points observed, 1245 and 2185 meters (4250 and 7200 feet) from the observing station, showed the lowest average motion: each at exactly 3.66 cm (.12 feet or 1.44 inches) per hour and 2.88 feet (87.78 cm) per day. At the middle station 1737 meters (5700 feet) from the instruments, the speed was recorded at 5.49 cm (. 18 feet or 2.16 inches) per hour and 131.67 cm (4.32 feet) per day.
In reporting these data, it must be pointed out that they simply have yielded a preliminary feel for the speed of the movement of the Khumbu Icefall. It is now clear that this movement is significantly slower than was expected, but fast enough so that a carefully-planned series of observations, day and night, at 3-hour intervals, would be of real interest. However, if this is done, the party that undertakes the work must field two separate teams of competent people: one 2-person pair to make the distance measurements from the excellent location which we used this year—and another team of at least two to tend the prisms in the icefall. Reliable radio communication is, of course, required between the teams. All personnel of climbing expeditions in the icefall at that time must thoroughly understand what is being done and the prisms well-marked and signed so that they will not be disturbed. For ease of access, we feel that they should be set near the climbing trail in the icefall, but not on it.