While we often assign metaphorical attributes of strength and fortitude to mountains as well as longevity and even divine immortality, they are, in fact, more fragile and less resilient than they appear. As D. N. Wadia and others have observed, the paradox of mountains is that they represent &lsquoweaker belts of the earth&rsquos crust&rsquo which are more susceptible to seismic activity. Recurring earthquakes have shown how unstable the Himalaya can be, as their moorings shift and buckle. Seemingly solid rock is shaken or rises and subsides along fractured fault lines. But almost as dramatic as these periodic and violent tremors are other, more subtle, distortions and anomalies that reveal the impermanence of the mountains and raise larger, fundamental questions about the origins of the Himalaya.
In 1802, When the Great Trigonometrical Survey of India was launched, East India Company surveyors began the laborious task of measuring and mapping the subcontinent, through a process of triangulation. Historian John Keay, in his book The Great Art The Dramatic Tale of How India was Mapped and Everest was Named, describes how this feat of cartography was accomplished. With theodolites, perambulators, spirit levels, measuring rods and plane tables, the surveyors established benchmarks and wove an intricate web of measured lines and angles, stretching from the southernmost tip of India to the summits of the Himalaya. While these &lsquocompass-wa11ahs&rsquo, as they were known in Anglo-Indian slang, worked their way up the peninsula, they soon discovered that the pull of gravity exhibited puzzling inconsistencies, which set their calculations awry and made them question the laws of physics. Surprisingly, it was a man of faith rather than science who came up with the answer. In 1854, Reverend J. H. Pratt, the archdeacon of Calcutta, put forward the idea of &lsquomountain compensation&rsquo. In essence, he proposed that the enormous mass of a mountain range generates gravitational deviations.
As Keay explains, the Survey of India tested Pratt&rsquos hypothesis at its headquarters in Dehradun, which lies at the foot of the Central Himalaya and at the northern end of the Great Arc. They conducted a variety of experiments with plummet lines and pendulums to determine the gravitational deflection caused by the presence of the mountains. Not all the results confirmed the Archdeacon&rsquos prophetic pronouncements. Occasionally, even in the absence of mountains, the readings from the surveyor&rsquos instruments were skewed and when the mass of the Himalaya was computed, the projected angle of &lsquotopographic deflection&rsquo did not correspond to their apparent size and stature. But as the surveyors soon realized, the mountains we see, like the tips of icebergs, are only the visible portions of a much larger mass suspended below. Out of Pratt&rsquos hypothesis came the concept of isostasy, the state of equilibrium that exists in the earth&rsquos crust, both the protruding peaks overhead and the deep substratum that extends beneath subsequent geodesic surveys have shown that the imposing magnitude of the Himalayan chain sits atop immense foundations of both solid and molten rock of varying densities.
Another anomaly that confounded geologists and surveyors was that certain rock formations sometimes cause a compass needle to deviate from pointing north. At first, this was blamed on lightning strikes, which can alter the surface magnetism in stones. But the explanation did not satisfy most scientists who gradually realized that some stones retain an indelible &lsquomemory&rsquo of their creation, specifically the position they once held in relation to the polarity of the earth. This means that as the earth&rsquos crust shifted and plates rearranged themselves, each layer of rock preserved an innate sense of direction according to its origins.
Palaeomagnetism became a serious field of study in the early nineteenth gravitational deviations.
As Keay explains, the Survey of India tested Pratt&rsquos hypothesis at its headquarters in Dehradun, which lies at the foot of the Central Himalaya and at the northern end of the Great Arc. They conducted a variety of experiments with plummet lines and pendulums to determine the gravitational deflection caused by the presence of the mountains. Not all the results confirmed the Archdeacon&rsquos prophetic pronouncements. Occasionally, even in the absence of mountains, the readings from the surveyor&rsquos instruments were skewed and when the mass of the Himalaya was computed, the projected angle of &lsquotopographic deflection&rsquo did not correspond to their apparent size and stature. But as the surveyors soon realized, the mountains we see, like the tips of icebergs, are only the visible portions of a much larger mass suspended below. Out of Pratt&rsquos hypothesis came the concept of isostasy, the state of equilibrium that exists in the earth&rsquos crust, both the protruding peaks overhead and the deep substratum that extends beneath subsequent geodesic surveys have shown that the imposing magnitude of the Himalayan chain sits atop immense foundations of both solid and molten rock of varying densities.
Another anomaly that confounded geologists and surveyors was that certain rock formations sometimes cause a compass needle to deviate from pointing north. At first, this was blamed on lightning strikes, which can alter the surface magnetism in stones. But the explanation did not satisfy most scientists who gradually realized that some stones retain an indelible &lsquomemory&rsquo of their creation, specifically the position they once held in relation to the polarity of the earth. This means that as the earth&rsquos crust shifted and plates rearranged themselves, each layer of rock preserved an innate sense of direction according to its origins.
Palaeomagnetism became a serious field of study in the early nineteenth century, initiated primarily by the German scientist Alexander von Humboldt, who persuaded the British East India Company to sponsor a Magnetic Survey of India alongside the ongoing Great Trigonometrical Survey. The Schlagintweit brothers, Robert, Hermann and Adolph, were dispatched on this mission. Much of their exploration took place in the Himalaya, all the way from Kanchenjunga in Sikkim to Nanga Parbat in Kashmir. From the nineteenth into the twentieth century, scientists continued to puzzle over the magnetism of rocks, which ultimately supported the theory of plate tectonics. It was only in 1906 that Motonori Matuyama and Bernard Brunhes demonstrated that the earth&rsquos polarity had been reversed less than 800,000 years ago. The fact that different generations of rocks held onto their original orientation relative to the shifting surfaces of the globe, allowed geologists to compile a more accurate timeline of the earth&rsquos formation. Using new tools like magnetometers, geologists were able to calculate the age of different strata in the Himalaya, which had been shuffled through tectonic upheaval.
The unsettling idea that various layers of Himalayan rock are pointing us in opposite directions proves that these mountains are not as permanent or immutable as they might seem, but formed out of geological migration. The stratified fragments of the earth&rsquos crust that make up these tiered ranges have wandered here from disparate parts of the globe and from diflerent epochs. The provenance of those tectonic journeys is locked into the magnetic memory of stones, each of them a compass that directs us towards continents that no longer exist.
Extracted from Wild Himalaya by Stephen Alter (Aleph, INR 899)
