2 Origins

2

Origins

From Tapovan, where sannyasi reach out to touch the mind of Brahma, you can turn your back on Shivling and look north across the Gangotri glacier to a towering line of peaks – the Bhagirathi range – framed against the indigo sky. Most impressive of all is the vast south wall of Bhagirathi III, around two kilometres high, a sumptuous vertical granite cliff capped with crumbling black shale. During our expedition in 1995, Bhagirathi III looked to me like the fragment of a colossal chessboard, black on white. I was intrigued at this contrast between the granite, which was much lighter in colour than granites I knew elsewhere, and the black shale above. Granites in the Himalaya are unusually pale, known as leucogranites, leuko being Greek for white. Their geochemistry is unusual: tourmaline, red garnet, much white mica and less black. I didn’t know it then, but there in front of me was a snapshot from a continuing process millions of years in the making – and unmaking – of the greatest mountains on earth.

A few years before I climbed Shivling, a geologist called Mike Searle,

now a world expert on the formation of the Himalaya, arrived at Tapovan with the ambition of climbing a new route on the mountain, not just for fun, but because it seemed the most effective way of collecting granite samples from different altitudes. Searle was trying to answer an obvious question that proved surprisingly difficult: when did the mountains of the Himalaya reach their current elevations of up to seven and eight thousand metres? By collecting samples and studying elements locked inside minerals within the granite, Searle and his colleagues could produce a plausible timescale of when and at what depth in the earth’s crust the granite first melted and then cooled as it was exhumed by uplift and erosion on the surface.

The route he and his climbing partner Tony Rex chose was great for

collecting samples but unnervingly dangerous, exposed as it was to avalanches rushing down the mountain’s north-west face. On their second day the weather turned and they found themselves trapped in a bitter storm. That night there was nowhere even to sit down and so they just stood there, jacket hoods cinched tight, buffeted by wind and spindrift, waiting for dawn. In the middle of the night they heard a loud crack above them, like an explosion, followed almost immediately by an immense rock fall. There was no longer any question of going to the summit. They now had to abseil a near-vertical kilometre and a half down to the flat glacier below, collecting samples of granite as they went. (For obvious reasons, this was always going to be done on descent.) Slowly their rucksacks filled with heavy rocks and when they stopped to brew some tea, they agreed it would be much easier to put all the rock samples in one rucksack and then drop it down the mountain. What could possibly go wrong? They watched the rucksack gather speed, before it hit a rock sticking out of the snow slope and burst, showering the mountain with rock samples, each in its own annotated plastic bag. They spent the next three hours climbing down and collecting as many as they could find.

To date the rocks back in the laboratory, Searle and his colleagues

measured the radioactive decay of two different isotopes of uranium, a technique only developed in the 1980s. This showed the granite he had collected from near the summit crystallised from molten magma twenty-three million years ago. Tests also showed that Searle’s samples had been exhumed rapidly from the time when they solidified to around fourteen million years ago, when their ‘exhumation’ slowed markedly. Erosion then accelerated at the start of the Quaternary glaciations about two and a half million years ago, which resulted in the landscape I was looking at across the Gangotri glacier. The black shale this molten granite had intruded was sedimentary and much older: from the Palaeozoic Era, around five hundred million years ago. Where the granite and shales had met, chunks of the original rock, called ‘country’ rock, had been ripped out by the liquid granite and then frozen in place as it cooled. Searle and his team used their results to suggest a model of orogeny – mountain-building – in the Himalaya that reached its peak between twenty and twenty-three million years ago. Their next task was to collect granite samples from other locations to see if their model worked across the entire Himalaya range.

I had read about Searle’s adventures and we had friends in common. One

told me how Mike had filled a barrel with rock samples at the end of a remote valley in the Karakoram, north of the western end of the Himalaya, and hired a porter to carry them back to the road-head, several days’ hard trekking down a glacier heaped with rubble. The porter, not unreasonably, wondered why anyone would want rocks from the far end of the glacier, when there were lots of perfectly good ones much closer to home. So he emptied the barrel Mike had given him, refilling it when they arrived. Mike, my friend told me, took the news philosophically.

I heard this story camped in the Gangdise mountains, a hundred

kilometres or so north of the main Himalayan chain, high on the Tibetan plateau. Later in that same trip, sitting in the garden of a hotel in Nepal’s capital, Kathmandu, my friend spotted Mike who was just back from another research trip. We asked him about the landscape of the Gangdise, which is such a contrast to the crammed chaos of the Himalaya: huge peaks at a distance from each other, like galleons afloat the vast brown plateau of Tibet. For the next half hour, Mike spoke clearly and simply about the origins of the Himalaya, how they had formed and the impact on what had been the south coast of Asia, when the high country we had stood on overlooked the shrinking Tethys Sea that in the Mesozoic Era separated the continents of Gondwana and Laurasia. The scale of time and space was inconceivable to me, unimaginable, and yet Mike seemed to watch the surface of the earth crease and buckle over millions of years under the gaze of his mind’s eye. It seemed a story as fantastical as Hindu myths of earth’s creation.

Our understanding of how mountains form is surprisingly recent. Long

after the mountains had been mapped, we knew more about the geology of the moon than how the Himalaya formed. When Mike Searle was a student in the 1970s, the idea of plate tectonics, of land masses moving across the earth, had only recently become mainstream. Its parent theory, the idea of continental drift, had been posited in 1912 by the German meteorologist and geophysicist Alfred Wegener. Until then, geologists believed the earth’s major geological features had been fixed when the molten surface of the planet cooled. Early attempts on Everest offered some clues. Alexander Heron produced the mountain’s first geological map after the reconnaissance of 1921. Geologists Noel Odell in 1924 and Lawrence Wager in 1933 both collected sedimentary limestone from near the summit. It was clear the top of Everest had once been at the bottom of an ocean. How this ocean floor came to be nine kilometres above the surface of the earth was, before plate tectonics, less obvious. Seeing the conformity of Everest’s summit rocks, all three assumed they had been pushed upwards but how that happened remained unproven.

When Wegener died of exposure on the Greenland ice cap in 1930, his

theory had supporters, like the British geologist Arthur Holmes, who theorised that convection deep in the earth might drive the continents across its surface. But the majority opinion was against Wegener, sometimes bitterly so: it became a battle between the ‘drifters’ and the ‘fixists’. After the Second World War, the scientific case for Wegener’s idea of whole continents splitting apart and colliding began to build. Mountain ranges were discovered in the deep ocean, where magma had welled up through cracks in the ocean floor and then crystallised. Magnetometers designed to detect submarines were used to survey the seabed, where basalt rocks recorded the earth’s polarity at the moment of their formation. The surveys showed this variation in black and white stripes, like a zebra’s, as the earth’s polarity flipped periodically from north to south and back again. This was clinching evidence that the ocean’s floor was spreading apart. The continents really were on the move. Wegener’s idea was proved correct, if not in every detail. You can trace on a map India’s northward drift in the sequence of volcanoes that stretch from Réunion, east of Madagascar in the Indian Ocean, via the Chagos and the Maldives to the Western Ghats, east of Mumbai. A ‘hot spot’ anomaly deep in the earth’s mantle where Réunion is currently located created all these volcanoes, each in turn cooling as it drifted away to the north.

There aren’t any fossils of sea creatures younger than fifty million years

in the Himalaya. This suggests that the collision of India with Asia that produced the mountains occurred around this time. That makes the Himalaya a youthful range in comparison to its near neighbours. Metamorphic rocks in the Hindu Kush, for example, are three times older, suggesting a much earlier process of mountain building. As the youngest and highest mountain range in the world, the Himalaya was the obvious place to study how continental plates collide. By calibrating magnetic anomaly stripes recorded in the Indian Ocean, geologists reconstructed how in the last one hundred and twenty million years India rifted from Antarctica and drifted north, following the breakup of the huge supercontinent Gondwana in the Southern Hemisphere.

Over tens of millions of years the Tethys Sea narrowed and then almost

entirely disappeared. The Persian Gulf remains as a tiny vestige of this ancient ocean, an elderly neighbour to the much younger Red Sea, which is widening by a centimetre every year. As India and Asia closed together, at latitudes around the equator, the Tethys seabed was lifted up into the sky. Most of it has long since eroded away; only smashed up fragments remain in the Himalaya. But in Oman in eastern Arabia, where the Tethys has yet to close, these formations, known as ophiolites, remain intact. It was here that Mike Searle began his research career, as though marching back in time to the dawn of the mountains he spent his life studying.

Following the initial collision, India ploughed on northwards, folding the

surface like the crushed bonnet of a geological car wreck. The Indian plate plunged underneath Asia. Volcanic activity along the former coastline of Asia fizzled out as the cold Indian plate slid beneath it. And it’s still going, converging at around fifty-five millimetres per year, rotating very slightly anticlockwise. Eight hundred kilometres of the Indian plate has already disappeared under Asia. The earth’s crust under Tibet doubled in thickness to seventy or eighty kilometres as it was jacked up into the air, creating a desert plateau with an average altitude of five thousand metres. India’s lithosphere, that is the crust and upper mantle, extends under the Tibetan plateau north of Everest by more than three hundred kilometres.

The plateau itself is far drier than the southern side of the mountains. The

Himalaya may be the abode of snow, but there’s remarkably little of it north of the mountains. There’s good reason most of the Himalayan population lives south of the range in the wetter middle hills. Ngari Prefecture in western Tibet receives less than seven centimetres of precipitation a year; Arunachal Pradesh, on the southern slopes of the eastern Himalaya, is the second wettest state in India, getting on average three metres of rain a year. As a consequence, erosion rates are low in Tibet and the uppermost layer of rock remains intact, so studying formations beneath it is difficult. In the Karakoram to the north-west, by contrast, far greater rates of erosion have exposed their structure in the most dramatic mountain landscapes in the world. The Tibetan plateau itself is being extruded east, towards south-east China, creating rift valleys between the mountains.

Where tectonic plates meet is termed the suture line. Around the

thousand-year-old Lamayuru monastery in Ladakh, the sparsely populated region to the west between Kashmir and Tibet, you can see the suture of Asia and India clearly in the surface rocks. To those armed with a little knowledge, formations like these are among the greatest wonders of the Himalaya. The degree of folding you see exposed in the Himalaya is testament to the planetary scale of the forces at work. Most mountains flatten out when viewed from the International Space Station at an altitude of around four hundred kilometres. The Himalaya do not: the mountains form a vast crescent, the biggest of big bananas, between the near-sea-level plains of India and the gigantic high plateau of Tibet, corrugated with the ceaseless impact of numberless glaciers and rivers, grinding and washing the mountains away.

The Himalayan suture line extends east for some 2,400 kilometres from

near where the Indus turns south around Nanga Parbat, ninth highest peak in the world and four hundred kilometres north-east of Islamabad, to where the Brahmaputra, called the Yarlung Tsangpo in Tibet, turns south around Namcha Barwa, due east of Tibet’s capital Lhasa. These points, like brackets or quotation marks, are termed syntaxes. While the length of the Himalaya records a head-on collision between India and Asia, south to north, at these corners, the squeeze comes from every angle. As a consequence, the massif of Nanga Parbat is currently rising faster than anywhere else on earth; the presence of so many warm springs in the region shows how rapidly the hot lower crust is being lifted. Rocks here are the youngest in the Himalaya, formed deep in the earth and then elevated with astonishing speed to the surface and on up to the highest altitudes. Geologists working on Nanga Parbat have found migmatites, a kind of partially melted gneiss that formed only a million years ago at depths of between ten and twenty kilometres. These migmatites are now found at altitudes up to eight kilometres. That means they have been exhumed at around eleven to thirteen millimetres each year, the fastest rate ever recorded on the planet. The story at Namcha Barwa, the eastern anchor of the Himalaya, is similar, although geological mapping here is more challenging. The topography is extreme: deep gorges thick with jungle. Data collected along the fabled Yarlung Tsangpo gorge, so remote it was only fully explored in the twentieth century, suggests the mountain-building process is only a little slower than at Nanga Parbat.

The granite I could see from Tapovan told another part of the story that is

equally staggering. As the India plate dived under Asia and melted, some of its molten core was squeezed back southwards into the weakness between the two plates, what’s called a mid-crustal channel, under the immense weight of the crust above, like an elephant sitting on a tube of toothpaste. In places, this ductile granite was able to balloon into colossal formations, like the one I could see on Bhagirathi. The south-west face of Everest is the upper boundary of this mid-crustal channel. The lower part is gneiss and granite rocks that were molten as recently as fourteen million years ago, squeezed under sedimentary rock twenty times its age, much of which has now eroded away. Where the ductile granite met the limestone, the country rock metamorphosed into marble, a feature on Everest known as the Yellow Band.

The sedimentary rocks at the summit of Everest are layers of lime

mudstones. The famous features of the mountain that so obsessed the British expeditions of the 1920s and 1930s, particularly the Second Step, are limestone crags standing proud of the shale beneath. In 1964 the Swiss geologist Augusto Gansser published Geology of the Himalaya, which included an image of the stem of a fossilised crinoid or sea lily collected by the first Swiss climbers to reach the top in 1956. (Gansser had travelled the length of the Indian Himalaya two decades previously as part of Arnold Heim’s Swiss scientific expedition; the pair coined the phrase Main Central Thrust for the core of metamorphic rock extruding south across the length of the Himalayan arc. Gansser also crossed the Nepali border without permission into Tibet and made a circumambulation of Kailas, dressed as a pilgrim, noting its geology as he travelled. Before setting out, a monk gave him a bag of small pills that would cure any illness he might encounter. It was these pills, Gansser liked to joke, that were the source of his longevity. He died in 2012 aged a hundred and one.) Gansser’s image of the fossilised sea lily proved the top of Everest to be the remains of an ancient ocean floor, which makes the human experience of standing on it all the more extraordinary. Lawrence Wager, who also collected rocks in 1933 during a brave attempt at the top, was in the 1950s head of the geology department at Oxford. He judged his samples were formed at the end of the Carboniferous, around three hundred million years ago. Their age is now more firmly fixed in the Ordovician, making them more than four hundred and forty million years old.

Deep time is hard for the human mind to conceive but the radically

different ages of rocks on Everest, and the processes that put them there, tear at our instinct to regard mountains as unchanging. The truth is the Himalaya are being made and unmade constantly. Mike Searle and his team discovered that rocks high on the Karakoram peak of Masherbrum had been formed at depths of about thirty-five kilometres, meaning everything above those rocks had been eroded away: fractured, split, gouged, scraped, crushed and washed downstream towards the sea. A quarter of the rock sediment washed into the world’s oceans comes from the Himalaya. It arrives in the Bay of Bengal at a rate of a billion tonnes a year, settling on the seabed to form what is known as a submarine fan. The Bengal Fan, the largest such feature in the world, extends three thousand kilometres south into the Indian Ocean and spreads to a width of fourteen hundred. Off the coast of Calcutta it reaches a thickness of eighteen kilometres. With that sort of pressure, the rocks at the bottom are themselves metamorphosing, and so gravity and time spin the wheel of the planet’s making.

*

For humans encountering the Himalaya, the very greatest of its impacts is climatic. Stand on the summit of a high mountain along the chain and, if it’s clear, you can look north towards the arid brown of the Tibetan plateau. Then, having turned ninety degrees in either direction, you take in an apparently endless sequence of ridgelines, each of them marking the limit of another river that has carved it out. On one side a desert, on the other some of the wettest places on earth. The contrast is startling, the explanation even more so. As the Tibetan plateau was lifted into the atmosphere, there was less air to interrupt the heat of the sun. As a consequence, the plateau gets hotter than land at sea level; it acts like a vast hot plate that through convection pumps the air above it into the upper troposphere. This in turn draws in a warm, moist wind from the Indian Ocean: the South Asian monsoon. As this air reaches the Himalaya, it rises and cools and its moisture precipitates. It is the action of all that water falling as rain and snow on the south side of the mountains, unable to cross the barrier of the mountains to the north, that has created landscapes so vastly different.

At times the monsoon falters: there is evidence that the population centre

around the fortress of Tsaparang in western Tibet failed in the early seventeenth century as the monsoon weakened, drying up fields that were once fertile. The reasons for this are as yet poorly understood but monsoons also weakened in the 1980s and scientists were able to correlate this to a cooling of the Tibetan plateau. The impact of all that hot air rising from the plateau on the jet stream and the global climate is not yet fully understood. There has until recently been a vacuum of data from the region but in recent years Chinese researchers have placed sensors even the plateau’s remoter corners to measure heat rising from all types of land surface. It’s hoped that more and better data will improve monsoon climate models, and with better forecasting comes the possibility of saving lives.

Not only does the monsoon intimately affect the hundreds of millions of

people who live in its shadow, the rise of Tibet may have impacted the earth’s climate as a whole. When the monsoon began isn’t certain, but it strengthened markedly seven million years ago, again connected to the rise in altitude of the Tibetan plateau. The palaeoclimatologists Maureen Raymo and William Ruddiman and oceanographer Philip Froelich have linked this increase in rainfall to an increase in chemical weathering, which occurs when carbon dioxide dissolved in rainwater reacts with minerals in the rock, locking it out of the atmosphere. Their theory suggests this process increases during periods of mountain building, because more material is being eroded into rivers. The higher the Tibetan plateau rose, the more rain fell, increasing erosion rates and speeding up the process of chemical weathering. As more carbon dioxide was locked away, the planet cooled, leading to the Pleistocene ice ages that so markedly shaped human history. It is a controversial theory, but there is tantalising evidence supporting it. Climate scientists use the ratio between two oxygen isotopes captured in marine limestone as a proxy for temperature: the greater the ratio the cooler the planet. There is a marked correlation between the timing of this global cooling and the rise of the Himalaya. The Tibetan plateau continues to impact global weather systems; Xiangde Xu from the Chinese Academy of Meteorological Sciences has reported that not only does the Tibetan plateau affect rainfall in China but there is a correlation between greater snowfall on the plateau and warmer Canadian winters.

The combination of rainfall and elevation in the Himalaya is reflected in

the immense river systems that drain the mountains. It is not the mountains that frame human activity in the Himalaya: it is the rivers. The three great rivers of East Asia – the Salween, the Mekong and Asia’s longest, the Yangtze – all rise close together on the eastern end of the Tibetan plateau. No wonder bridge-builders have been so admired here. Some of the greatest rivers predate the Himalaya’s rise, including the Indus and the Yarlung Tsangpo– Brahmaputra. Others began with the mountains, including the Ganges and the great river systems of Nepal. These have eroded deep into the mountains, in places right across their axis. The head of the Arun river in Nepal has cut through east of Makalu, the world’s fifth highest mountain, to within just ten kilometres of the Yarlung Tsangpo. As the process continues, the Arun will ‘capture’ the Yarlung Tsangpo and the headwaters of this great river will subsequently flow through Nepal.

It is the combination of altitude and climate that makes the Himalaya so

formidable and so formidably diverse. At its narrowest the distance between the plains, or terai, to the south of the mountains and the Tibetan plateau is around a hundred and fifty kilometres. Within that distance the gain in altitude is as much as eight kilometres. Remember that with every kilometre gained in altitude there is a drop in temperature of more than six degrees Celsius. Altitude acts in a similar way to latitude, meaning that in the briefest distance you can move through a wide range of ecosystems: subtropical broadleaf forests in the Siwalik foothills, mixed temperate forests of oak and rhododendron in the middle hills, firs and pines at higher altitudes. Juniper has been found growing in Bhutan at over 4,700 metres, but for the most part the trees thin much lower. Pastureland above the tree line can extend well over five thousand metres. Above that, you are in an ecosystem more akin to the Arctic.

Thanks to altitude, the biodiversity of the Himalaya is astonishing,

especially in the eastern part of the range where the monsoon is so strong: eastern Nepal, Sikkim, Bhutan and the Indian state of Arunachal Pradesh. Sikkim, only a little bigger than Delaware, or the English county of Cumbria, has six hundred and fifty different species of orchid. Nepal has a similar number of butterfly species, roughly the same as the whole of the United States, a country more than sixty times its size. At high altitude across the Himalaya are blue sheep, musk deer, red pandas, wolves and snow leopards. In the middle hills I’ve seen leopards, Himalayan bears and langurs, black faces fringed with white fur. In the southern subtropical foothills are tigers, Asian rhinos and wild elephants. In the rivers are dolphins and gharial, a species of crocodile. There are poisonous snakes too, vipers and cobras, another significant risk to life and a major cultural trope on either side and at either end of the mountains in the form of nagas, serpent spirits. Hunting and foraging have been a fact of life for many Himalayan ethnic groups for millennia and even now there is still one group, the Raute, who remain hunter-gatherers. The forests and mountainsides are not just a larder or a place to find building materials: they are a treasure trove of medicinal plants. One of the best-known trades in the Himalaya is in yartsa gunbu, meaning ‘winter worm, summer grass’ in Tibetan, a caterpillar infected with a fungus that grows like a plant and is worth its weight in silver on the Chinese market.

The natural hazards of such a rapid rise in elevation are complex and

unpredictable: floods, earthquakes and landslides, but also less obvious dangers, such as glacial lakes draining almost instantly and catastrophically. The most famous example of this was a lake of ten square kilometres near Mount Machhapuchhre in the Annapurna region, which collapsed in the mid sixteenth century, sending a wall of water and five cubic kilometres of debris into the Pokhara valley. These events, called Glacial Lake Outburst Floods, are of great concern today as climate change prompts glacial retreat. Landslides also cause flooding, as they did most notably in early 1841, when a mountain spur on the west side of Nanga Parbat detached and fell into the Indus, creating a dam. A lake quickly formed, and the king of Gilgit, Karim Khan, sent notes written on birch bark and floated downstream, warning that a flood was imminent. When the dam broke in June, a huge wall of water swept down the Indus destroying hundreds of villages and killing thousands of people and their animals. A Sikh army camped near the river outside Attock in northern Punjab was engulfed and five hundred men died in an instant. A survivor, a zamindar or commander, described it thus: ‘As a woman with a wet towel sweeps away a legion of ants, so the river blotted out the army of the Raja.’ The waters at Attock rose fourteen metres above the normal summer flood level. And while exceptional in its scale, the 1841 disaster was far from unique: Henry Strachey, older brother of John, heard of a similar event in 1835. Floods caused in this way continue to kill along the length of the range.

Earthquakes have been a regular disruptive force throughout Himalayan

history. They are mentioned in the Mahabharata and later Buddhist texts. We know a major earthquake in 1255 rocked Nepal’s Kathmandu valley. Even so, despite an extensive literature of historical annals, there is a dearth of accounts. We know there was a series of earthquakes in the sixteenth century, including one in Kumaon in 1505, but it was only in the colonial period that systematic records began to be kept. One of the most important accounts, for its detail and insights, is from 1897, when Richard Dixon Oldham of the Geological Survey of India witnessed an earthquake of magnitude 8.7 in Assam. A fault on the northern side of the Shillong plateau was displaced by as much as sixteen metres and the northern part of the plateau was lifted instantly into the air by eleven metres. Loss of life was surprisingly low, but houses were destroyed across an area three times the size of England.

Geologists call mountains high-energy environments and the immense

physical and natural diversity in the Himalaya is reflected in a high-energy human population. Because differences in climate and environment come thick and fast as you move across terrain, the cultural habits that have arisen in response to those differences are intensely focussed. While the monsoon is the region’s major weather system, local climate, even from one side of a valley to the other, can be astonishingly different; a south-facing slope can have a growing season of a month longer. Himalayan people understand very well the French concept of terroir. This diversity is reflected in language: there are more than seventy distinct languages and dialects in Nepal alone. Yet despite this localism, people have always been on the move in the Himalaya. Across the mountains, traders have exchanged Tibetan salt for Indian grain for millennia, a trade only recently disrupted by the arrival of roads. The seasonal migration of herders taking animals to high pasture is another practice that has endured. Population growth and urbanisation is changing the region’s human face faster than ever, and politics with it. Climate change is having a greater impact here than almost anywhere else. Yet, as we shall now see, the adaptations people have made to thrive in this extreme environment not only reach the roots of their culture, they also extend to their genetic code, creating a human suture line unlike almost anything else in human history.

OceanofPDF.com