The World's Great Mountains: Not the Height You Think
The World’s Great Mountains: Not the Height You Think
Terris Moore
It has been little noted, except perhaps by geophysicists and mountaineers, that Mount Everest is not, if absolute methods of measurement are used, the highest mountain in the world. Nor are the Himalayas the world’s highest range, if we ignore the idea of a sea-shore at their base which actually is hundreds of miles distant out of sight around the bend of the earth — and measure instead the height of Mount Everest from the center of the earth. That unique spot is a more precise location; and it is the one single point nearest in distance to all the world’s great mountains, the two most important ranges of which are found on opposite sides of the globe from each other.
By this absolute yardstick of reference, it can be shown that the world’s highest mountains are the great Andes of the equator: Chimborazo, Huas- carân, and Cotopaxi. Their three summits all rise higher from the center of the earth than does the summit of Mount Everest. Reason: the earth is not the perfect sphere one might casually assume. Instead, flattened by centrifugal force from the thousand-mile-an-hour (at the equator) spin of its rotation, the earth’s polar diameter is some 26.7 miles shorter than the mean of its infinitely numerous equatorial diameters. The result is that Chimborazo, located at about 2° S. latitude, rises some 1¼ miles higher from the center of the earth than does Mount Everest in 28° N. latitude. So also does the summit of Huascarán located at 9° S. latitude in Peru; and indeed a close contest remains as to whether Chimborazo or Huascarán is the “highest mountain in the world,” with the ultimate determination perhaps best made from gravity observations on their summits. Cotopaxi, the highest active volcano in the world — however one makes the measurement, whether by gravity readings to determine the height from the center of the earth, or whether by the height above a hypothetical “sea-level” beneath its summit — is clearly number three. From the center of the earth it tops Everest’s summit by about 1 mile. The exact measurements setting forth all the above may be of interest to some; but as to those details of geophysics, more later, in the appendix.
This seldom-used method of measuring the heights of mountains has a certain believe-it-or-not appeal, and provides a new way of looking at geophysical relationships. But from the point of view of human activity, barometric pressure, not distance from the earth’s center, is the factor of greatest importance in comparing very high mountain environments. And the levels of barometric pressure likely to be encountered are most readily — if only approximately — indicated in advance by geographical elevation above a theoretical sea-level. Elevation above sea-level however, ceases to be a reliable index of probable barometric pressures when comparisons are made between mountain ranges with differences in latitude so great as those between, for example, the Alaska-Yukon mountains and the Himalayas. The shape of the envelope of the earth’s atmosphere is flattened even more toward the Poles, and bulging even more toward the equator, than is the surface of the earth itself; and yet more in winter than in summer. For in addition to the gravity and centrifugal forces which flatten the shape of the earth’s geoid, in the case of the atmosphere which surrounds it there is the additional effect of temperature whereby the great heat of the tropics and the cold of the arctic expand the atmosphere upward over equatorial latitudes, and contract the atmosphere downward toward high polar latitudes, especially during the polar winter nights. So pronounced is this effect that though the geoid itself is flattened no more than 1/298, namely by about 1/3 of 1%, the atmosphere surrounding it is very much more flattened toward the poles and bulging upward over the tropics, indeed as much as about 14% for the northern hemisphere during its winter.
Thus the relation between barometric pressure and high mountain elevations is so loose that Dr. L. G. C. E. Pugh, the well-known Mount Everest physiologist, found pressures much higher in the upper Himalaya than he had expected. “Extrapolation from the data collected on Mount Everest in 1953 and Makalu in 1961 suggests that the pressure on the summit of Mount Everest, 29,028 feet… is equivalent to 27,500 feet on the standard altimeter scale. This affords some explanation for the seemingly impossible feat of ascending to within 1000 feet of the summit without supplementary oxygen, which has been done altogether by eight men.”1 And after Pugh wrote these words in 1962 yet more human feats were performed without oxygen high on Everest. An over-simplified, but not unreasonable, summary might be that “the high Himalayas, physiologically, turn out to be about fifteen hundred feet lower than one might expect from their reported elevations above sea-level.” And similarly, another summary might be that “the Alaska-Yukon mountains on the other hand seem to be, physiologically, about fifteen hundred feet higher than one might expect from their reported elevations above sea-level.”
Some of the scientific aspects of this rather esoteric phenomenon may be of interest to A.A.J. readers. This writer’s first association with it began thirty-eight years ago when still a graduate student and youngest member of the Alaskan mountain expeditions led by the late Allen Carpé (research engineer at Bell Telephone Laboratories) and the late Dr. William S. Ladd (then professor and later dean of Cornell Medical College in New York). From our 1931 expedition Carpé wrote: “It has been an interesting observation on all of the writer’s Alaskan climbs that the atmospheric pressures on the summits has corresponded to elevations about 10% greater than the actual. This has been shown by a number of barometers, and may be largely explained by the low average temperature and consequent greater density of the column of air from sea-level to the summit. Whatever the cause, air pressures on Mounts Logan, Bona, and Fairweather were those which, by usual reckoning, should be encountered at elevations of 22,000, 18,000, and 17,000 respectively”2 —[but these peaks of course are only 19,850, 16,400, and 15,300 feet respectively].
It was possible in 1931 for our group to postulate the outlines of the phenomenon. For in addition to the substantial body of barometric data then available from mid-latitude mountain stations (on which, indeed, the calibration scale of barometers was based), we also by then had sufficient data from the Alaska-Yukon subarctic mountains and from the great Andes of the equator to formulate the general latitude and seasonal effects of the phenomenon (Hudson Stuck with his mercurial barometer on McKinley in 19133, Abruzzi with his on St. Elias in 18974, and Edward Whymper with his mercurial barometer laboriously carried up Chimborazo and other Ecuadorian peaks5 in 1880). Ladd’s interest was in the physiological, which in those years was less closely concerned with the phenomenon. But Carpé, as an early member of A. H. Compton’s cosmic ray research team6, became aware that (because of the absorptive powers of the atmosphere for cosmic radiation) the phenomenon would appreciably affect the cosmic ray data he was about to collect on Alaskan mountains. Thus began our 1931 interest in assessing the parameters of the phenomenon. Regrettably Carpé was killed in 1932, still in his thirties, his scientific material about this phenomenon not yet sufficiently written up for publication. (Though Compton of course pursued and carried forward the cosmic ray research which had been of concern to him.) Ladd returned to Cornell to take up administrative duties. And my interest when I returned to graduate studies for advanced degrees, was sharply directed to the social sciences by the unprecedented economic collapse then gripping the country.
Recent professional interest in the subject of comparability between the higher Alaskan-Yukon mountains and counterpart high ground elevations in the Himalayas (for human activities) has prompted renewed and much more detailed investigation of the phenomenon which Carpé briefly described in his preliminary 1931 report. Today’s modern reference tables7 in which the phenomenon may be discerned, tell us that the altitude of the mid-line of the earth’s atmosphere (where the barometric pressure is half that of sea-level) fluctuates — in the latitudes of Mount McKinley and Mount Logan — just under 18,400 feet in mid-summer, but by mid-winter, because of contraction of the colder atmosphere, it drops to 16,880 feet. In latitude 30°, where the Himalayas are located, it stands as high as about 19.400 feet in mid-summer and drops to about 18,850 feet in mid-winter.
On Mount McKinley. A close analysis of exactly how this phenomenon manifests itself upon our well-known highest mountain vis-à-vis the Himalayas may be of interest; for the same will essentially hold true for the other Alaskan-Yukon mountains.
The summit of McKinley in all seasons of the year rises up far above the mid-line of the earth’s atmosphere; and to the greatest extent in midwinter. In January its barometric pressure at the 20,320-foot summit varies around a mean of only 426 millibars8. (Sea-level pressure averages about 1013.2 mb, each millibar being a thousand dynes per sq. cm.) To reach this same 426 mb level of low pressure in the latitude of the Himalayas, in mid-winter, one must climb nearly another twenty-five hundred feet (2,485 feet in the Air Force tables) ; and in mid-summer one must climb an additional thirty-one hundred feet (3,145 feet according to the tables). Thus when McKinley’s 20,320-foot high summit was being visited in mid-winter of early 1967 by individuals associated with the University of Alaska’s Institute of Arctic Biology, they moved into an atmospheric environment where the mean barometric pressure — which indicates the partial pressure of oxygen so important to climbers and physiologists — was that of Himalayan elevations in mid-winter, of about 22,800 feet (22,805 feet from interpolation in the tables), and in the Himalayan mid-summer, of over 23.400 feet (23,465 feet in the tables)!
In its mid-summer configuration, McKinley’s summit declines — in what might be called its “Himalayan analog elevation,” its millibar pressure rising from 426 to a mean of 459 for July. At this season its “simulate” value for Himalayan barometric environments declines to about 21,000 feet and 21,650 feet, for the Himalayan mid-winter and mid-summer respectively.
It might be asked whether these data, obtained from free air flights observations at 400, 450, and 500 millibar flight altitudes, are equally applicable to the same ground elevations. In theory, since “means” are used throughout, the data should be equally applicable because the use of means should eliminate the temporary disparities between free flight and mountain ground station barometric pressures caused by occasional strong local air mass flows over the mountain station. It may be worth noting, though in the case of Mount McKinley it will constitute a spot check only, that in the known instances when mercurial barometers were actually taken to the summit of equatorial Chimborazo (20,563 feet), 4-5 January, 1880, and the somewhat lower summit of Mount McKinley, 7 June 1913, the observed raw data now confirm to us what was then a seeming paradox: 14.11 inches of mercury on Chimborazo but only 13.6 inches of mercury on McKinley. Converted to millibars, the figure becomes 460 mb for McKinley, thus indicating (by its closeness to the 459 mb figure from the tables) that the mean values for barometric pressure at a given elevation on the mountain will be the same as the mean values at the same altitude in free air. A further confirmation of the point, but based upon more extensive data, comes from the University of Alaska’s Mount Wrangell station where daily mercurial barometer readings are available for a number of months9. And of course the general theory of this point may easily be investigated by those who doubt it from a comparison of the already available mountain station barometric data from middle latitudes against the data in the free air tables for those same latitudes and altitudes.
In addition, at the University’s Mount Wrangell station there is specific confirmation for the pattern of seasonal change in the range of barometric pressures, which is an essential part of the theory of the phenomenon we are describing. Pressures at Mount Wrangell have been found to range between 590-620 millibars during July-August, but to descend during March to a 572-586 millibar range9 when the mountain is in its winter “Himalayan analog” barometric configuration.
The effects of the phenomenon we have been describing decline in importance as one descends from Himalayan heights, and become insignificant as one approaches sea-level. Where the combined effect may amount to as much as over three thousand feet on the summit of Mount McKinley, on Alaska’s Mount Sanford (16,200 feet) it can amount to as much as a little over two thousand feet; and on Mount Wrangell (14,000 feet) it can amount to something under two thousand feet.
What about the effects of ambient temperature? By ambient we mean not the average temperature of the long air column up from sea-level, with which we have been concerned so far, but rather the air temperature of the very local environment right at the station. In the case of aircraft, their air-foils — wings, propellers, and helicopter rotors — are indeed very appreciably affected by the temperature of the air in which they are moving. Less lift in hot air, greater lift in cold. But in the case of animal and human lungs however, the availability of the partial pressure of oxygen to the lung tissue is not affected by the ambient temperature. For as Dr. Charles Houston, the authority on mountain physiology, has pointed out: “We need not take into consideration the temperature of ambient air…. since the inhaled air is instantaneously warmed to body temperature.”
What happens to the standard “wind-chill” tables at Himalayan elevations: are they valid there as at sea-level? And if so, should one employ the indicated wind speed as read direct from the anemometer; or instead, a correction for the true wind speed which will be faster than the indicated speed as one ascends to higher elevations? The answer is complex; so also the reduced capacity of human physiology to withstand wind-chill in the high thin air. The whole subject requires further research and elucidation.
APPENDIX A
Computation of Height above Earth’s Center for the Summits of Cotopaxi, Chimborazo, Huascarán, and Everest.
The values stated in the text were obtained by first computing the earth’s radii in meters to the surface of the “ellipsoid of reference” (assumed to be synonymous with the concept of “sea-level” where there is no sea) at the latitude of each of the four mountains; and then in each case adding the “height. above sea-level” as found in the most recent geographies, the latter converted to meters, all as sum- marized below.
Summit
Cotopaxi at
0°40'S — 6,384,043
meters
above
earth
center
"
Chimborazo
1°29'S — 6,384,407
"
"
"
"
"
Huascarán
9°08'S —6,384,384
"
"
"
"
"
Everest
27°58'N—6,382,328
"
"
"
"
Thanks are due Mr. O. M. Miller of the American Geographical Society who made the computations, using for "f” (flattening) = 1/298.3, and for "a” (equatorial radius) = 6,378,150 meters. So also, thanks are due Dr. Bela Szabó of the Air Force Cambridge Research Laboratories, who independently computed (and confirmed) the earth radii to the “ellipsoid of reference” at the bases of the four mountains; both in private communications to the author for this paper.
APPENDIX B
From Handbook of Geophysics & Space Environments—Air Force Cambridge Laboratories, 1965.
Table 3-23. Average pressure at various altitudes over North America, 90° to 100° W longitude.
Altitude
Pressure (mb)
(103 ft)
20°N
30°N
40°N
50°N
60°N
70°N
80°N
JANUARY
10
709
706
694
683
671
666
663
20
484
All
464
448
434
428
426
30
317
310
304
283
274
268
264
40
201
196
187
178
171
166
161
50
122
119
114
111
107
103
99
60
73
72
70
68
66
63
60
70
44
44
43
42
41
38
36
80
27
27
27
26
25
23
21
90
17
17
17
17
16
14
13
100
10
10
10
10
10
9
8
JULY
10
712
714
710
703
695
692
689
20
488
489
486
475
467
462
457
30
320
321
318
308
301
296
294
40
205
206
204
196
191
188
187
50
125
127
125
122
120
119
119
60
75
76
76
76
75
75
75
70
46
47
47
47
48
48
48
80
28
29
29
30
30
31
32
90
17
18
18
19
19
19
20
100
11
11
11
12
12
12
12
Table 3-24. Amplitudes of systematic pressure variations and time of maximum at Terceira, Azores [Harris et al, 1962],
Diurnal àemidurnai
Pressure
Level
Ampl.
Time
Ampl.
Time
(mb)
(ft)
(mb)
(h)
(mb)
(h)
Sfc
0
0.10
2100
0.50
0948
1000
400
0.10
1904
0.53
0950
950
1870
0.12
1824
0.46
0956
900
3390
0.16
1612
0.49
1002
850
4770
0.18
1604
0.47
1002
800
6650
0.20
1612
0.44
1002
750
8430
0.20
1616
0.38
1010
700
10,260
0.25
1548
0.37
1002
650
12,240
0.18
1608
0.40
1030
600
14,320
0.25
1608
0.33
1020
550
16,570
0.27
1508
0.33
1034
500
18,970
0.28
1516
0.29
1032
450
21,610
0.27
1424
0.24
1036
400
24,440
0.31
1504
0.24
1046
350
27,590
0.31
1504
0.20
1046
REFERENCES (Note numbers in text)
1 —Pugh, L. G. C. E.—British Medical Journal (8 Sept. 1962, vol. ii, p. 621-7).
2 — Carpé, Allen—The Alpine Journal (London) Nov. 1931, p. 227.
3 — Stuck, Hudson—The Ascent of Denali, New York, 1914.
4 — Abruzzi, Prince Luigi Amadeo—The Ascent of Mt. St. Elias, London, 1900.
5 —Whymper, Edward—Travels Amongst the Great Andes of the Equator, N. Y., 1892.
6 — Johnston, M. (edit.)—The Cosmos of Arthur Holly Compton, N. Y., 1967, p. 161-2.
7 — Air Force Cambridge Research Laboratories—Handbook of Geophysics and Space Environments, Bedford, Mass., 1965, p. 3-32.
8 — Appendix B—By interpolation from 434 for 20,000 feet at 60°N.
9 — Private communication to the writer from Professor Carl S. Benson of the University of Alaska faculty.