Why the highest summits are at low latitudes

By M. Michael BradyAmerican and European mountaineers have long known that, if you want altitude, go south. After Alaska became a State in 1959, Americans could add “or north” to that rule, as the elevation of the summit of Denali (Mount McKinley) is more than a vertical mile above any peak in the traditional continental 48 States. But the old rule still holds, as the summit elevation of Anconcagua in Argentina is the highest outside Asia and nearly half a vertical mile higher than that of Denali. Likewise, French mountaineers proudly point out that the summit of Mount Blanc is the highest point in Europe. But far south from there, the summit of Kilimanjaro in Tanzania is two-thirds of a vertical mile higher. Moreover, no summit elevations in the Americas, Europe or Africa can match those of the world’s hundred highest peaks in the Himalaya and Karakoram of southern Asia.

Scientists have long reasoned that the greater number of high mountains at low latitudes is more than just a coincidence. Save for volcanoes, three effects are known to effect mountain height: the extent of tectonic uplift, the strength of the Earth’s crust at that point and the nature of subsequent erosion. For years, schoolchildren have learned about the third of the three effects. Americans know that erosion wore the ancient Appalachians down to elevations lower than the newer Rockies, and Norwegians know that glaciation left their mountains lower than the Alps.

Yet the interplay between uplift and erosion is not straightforward, because feedback between the two may be involved and there may be a link to climate. Moreover, the strength of the Earth’s crust has effects not yet completely understood, although it’s thought to be decisive in limiting the elevations of large high plateaus, such as those in Tibet and in the central Andes. Many theories of the underlying mechanisms have been advanced, and earth scientists have been debating them for decades. But now research conducted by scientists at Aarhus University in Denmark has provided a unifying explanation.

David Egholm and colleagues at the University’s Department of Earth Sciences processed satellite images of all large mountain ranges at latitudes from 60° North to 60° South to extract accurate data on the land surfaces and elevations, as well as the average elevation of the snowline in each range. Glacial erosion was estimated by computer modeling. These data were then indexed to the latitude
of the range.

They found that the warmer climates of low latitudes drive snowlines up, which in turn leads to higher mountains. Erosion was found to be more significant above the snowline, where glaciation can limit summit height. The summit of a mountain is seldom more than five thousand feet above its snowline. So mountains with higher snowlines tend to have loftier summits.

Surprising as it may seem, this research came out of a small, pool-table-flat, low-level country. Denmark’s area is about a sixth that of the State of Colorado; much of it is near sea level, and its highest point is at an elevation of 551 feet. But in the sphere that counts in such matters, scientific competence, Denmark towers. Natural scientists cannot escape Oerseted of the 19th century in magnetics or Bohr of the 20th in quantum mechanics. And no philosopher can escape Kierkegaard. The University of Copenhagen celebrated its tenth anniversary before Columbus sailed to discover the New World. Academic rigor is the rule rather than the exception in Denmark.

Moreover, many of the notable contributions to mountaineering have been made by lowlanders. Edward Whymper, famed for his first ascent of the Matterhorn in 1865, was born and spent most of his life in London, at an elevation of 79 feet. Likewise, Edmund Hillary, famed for his first ascent of Mt. Everest in 1953, was born and spent most of his life in and near Auckland, New Zealand at elevations seldom more than 650 feet. Arguably, lowland location may be a prerequisite to understanding heights. But that connection has yet to be studied.

M. Michael Brady lives in a suburb of Oslo and takes his vacations in France. By education, he’s a natural scientist. His Dateline: Europe column appears monthly in the Gazette.

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