Ice Rivers

A Story of Glaciers, Wilderness, and Humanity

Jemma Wadham

• Éditeur: Princeton University Press
• Année: 2021
• ISBN:
  9780691229010
• Sujet: Ciencias físicas
• Sous-sujet: Geología y ciencias de la Tierra

A passionate eyewitness account of the mysteries and looming demise of glaciers—and what their fate means for our shared future The ice sheets and glaciers that cover one-tenth of Earth's land surface are in grave peril. High in the Alps, Andes, and Himalaya, once-indomitable glaciers are retreating, even dying. Meanwhile, in Antarctica, thinning glaciers may be unlocking vast quantities of methane stored for millions of years beneath the ice. In Ice Rivers, renowned glaciologist Jemma Wadham offers a searing personal account of glaciers and the rapidly unfolding crisis that they—and we—face.Taking readers on a personal journey from Europe and Asia to Antarctica and South America, Wadham introduces majestic glaciers around the globe as individuals—even friends—each with their own unique character and place in their community. She challenges their first appearance as silent, passive, and lifeless, and reveals that glaciers are, in fact, as alive as a forest or soil, teeming with microbial life and deeply connected to almost everything we know. They influence crucial systems on which people depend, from lucrative fisheries to fertile croplands, and represent some of the most sensitive and dynamic parts of our world. Their fate is inescapably entwined with our own, and unless we act to abate the greenhouse warming of our planet the potential consequences are almost unfathomable.A riveting blend of cutting-edge research and tales of encounters with polar bears and survival under the midnight sun, Ice Rivers is an unforgettable portrait of—and love letter to—our vanishing icy wildernesses.

PART ONE

The Smell of the Ice

1. Glimpses of an Underworld

The Swiss Alps

I was twenty, on my first expedition, a somewhat green Geography undergraduate working as a field assistant on a research project that aimed to uncover mysterious details about the flow and plumbing of the Haut Glacier d’Arolla, a small, relatively accessible valley glacier tucked up high in the Swiss Alps. I had pored for hours over the theories of glaciers in geography textbooks, of course, and was familiar with their handiwork from family holidays in the Cairngorms – but it was here that I would meet one for the very first time.

I had come completely unprepared, with a small rucksack full of mostly summer clothes, my brother’s old army boots (several sizes too big) and a plastic mac which had served me well in Scotland but boasted the breathability of a crisp packet. Camped at 2,500 metres above sea level in the rocky valley of the Haut Glacier d’Arolla, I had spent my first night sleeping on cardboard in an old sleeping bag I’d used for sleep-overs when I was eleven, with its thin walls of clumpy polyester fibres and all the heat retention of a hessian sack. At this point I’d never heard of Polartec, or Gore-Tex, or even the concept of a Karrimat. Constantly disturbed by the muffled roar of the glacial river not far below and the shotgun-like cracks of rockfalls on the slopes above, not to mention the thin air which laboured my breath and the cold that made my bones throb with pain, I’d barely slept. Suddenly I understood why glaciers had been considered the resting place of ghouls and evil spirits in medieval times.

So this is where it all began – my journey as a glaciologist. Of course, I was following the deeply grooved path of many before me. The European Alps have always been a prime stomping ground for glaciologists, with glaciers of all shapes and sizes mostly accessible by foot – from the elongated, streamlined twenty-kilometre-long ice tongue of the Swiss Aletsch Glacier to tiny, stubby glaciers which are barely noticeable, perched high up in concave rock depressions (cirques) above the wide plains far below. Spanning 1,000 kilometres between Nice in the west and Vienna in the east, the Alps are part of a much greater mountain system, the Alpides, which stretches as far as the western Himalaya. Mountains are always a sign of geological drama, and so it is for the Alps, which formed as the African plate began to creep north into the European plate around 100 million years ago.

During their most intense collision, around thirty million years ago, the two plates squashed old crystalline basement rocks and younger seafloor sediments from a pre-Mediterranean ocean, neatly folding them into a series of vertically stacked ‘nappes’ – rather like the sail of a boat when hauled in to be stored on the boom, fold overlapping fold. The rock was crumpled most vigorously in the western Alps, where the mountain belt is thinner but higher, and includes such giants as Mont Blanc – at 4,800 metres the pinnacle of western Europe. During the past two million years, the Alps have been reshaped and remoulded by intense phases of glacial erosion as the Earth has plunged in and out of long cold periods (glacials) and short warm periods (interglacials), which reflect natural oscillations of our climate caused by tiny shifts in the Earth’s orbit of the sun.

It was Jean-Pierre Perraudin, a mountaineer and hunter from Lourtier in the Valais region of Switzerland, not far from the Haut Glacier d’Arolla, who posited one of the first modern theories of glaciation.¹ He speculated around 1815 that oddly smoothed rock surfaces were caused by glaciers effectively ‘sanding’ the rock they flowed over, with any protruding rocks and stones in their basal ice layers gouging deep grooves in the direction of the ice flow. He observed that giant boulders strewn across the valleys near his home were of a foreign rock type, and must have been dumped there by a glacier when ice filled the valleys during the last glacial period. Although Perraudin had an intimate understanding of the mountains, still he had to toil against the prevailing belief of the day, which was that great biblical floods had been the protagonists in forming the alpine landscape. It seemed inconceivable to him that a flood could have dislodged and transported these giant boulders, which would clearly sink like stones. He spoke to the naturalist Jean de Charpentier about his findings, but de Charpentier dismissed them as ‘extravagant’ and ‘not worth considering’.²

It took another fourteen years for Perraudin’s theories about glaciers to be fully developed, first by Ignace Venetz, a highway and bridge engineer in Val de Bagnes and another native to the Valais region of Switzerland. He had attempted to create channels to drain meltwaters from a large lake which had grown at the edge of a local glacier when its ice advanced and dammed a stream – such glacier advances were common during such times and were a symptom of the final throes of a cold snap during the Middle Ages in Europe, popularly called ‘the Little Ice Age’. However, Venetz failed in his attempts, and the lake catastrophically flooded the valley and destroyed many lives and houses.

Venetz had many conversations with Perraudin about the inner workings of glaciers. By 1829 he was finally convinced, and presented his ideas at the annual meeting of the Swiss Society of Natural Sciences, which argued that the glaciers of his time were all that remained of a much larger mass of ice that once covered the Alps. This time, Jean de Charpentier supported him, now also swayed by these theories of massive glaciation. Yet it was Louis Agassiz, a Swiss biologist and geologist who grew up near Fribourg and ended up as a Professor of Natural History at the University of Neuchâtel, who, through a mixture of serendipity and determination, brought the early theories of glaciers to the fore in his famous Études sur les Glaciers in 1840. Agassiz is often lauded as the grandfather of glaciology, but in truth there were several, starting with Perraudin. They all applied pressure to the wall of conventional wisdom, until the wall weakened and ultimately collapsed.

The first time you wake up somewhere new in the mountains is always the most explosive for the senses. Dragging myself out from beneath my humble canvas on that first alpine morning, I was greeted by a panorama that remains one of the most memorable of my life. Directly across the valley an imposing mass of ice tumbled over a col (the saddle between two peaks) and down the seemingly vertical rock wall about five hundred metres in height – not a waterfall but an icefall, where the glacier meets the end of its hanging valley and must venture over the precipice below.

Here the glacier in question, the Bas Glacier d’Arolla, flows quickly down over the steep rock face, stretching until its tiny crystals can no longer deform fast enough to permit flow as a single mass, and the ice fractures in a million planes to form a chaotic field of crevasses and sharp ice towers, known as seracs. Icefalls are death traps to the mountaineer. Perhaps the most notorious example of an icefall can be found in the upper reaches of the Khumbu Glacier, the highest glacier on Earth, which moves at about a metre per day. This is one of the most treacherous parts of the ascent from base camp to Mount Everest’s summit in the Himalaya. Climbers can take as long as a day to pick their way through the glacier’s tortuous path, and it has caused several dozen deaths over the last fifty years – simply because ice flows, and the faster it flows the more difficult it becomes for it to move as a single body, leading to crevasse fields and icefalls.

A rather incredible feature of glaciers is that they have been found to flow in three possible ways, the slowest of which is through the deformation of glacier ice crystals. Ice behaves more like a liquid than a solid; technically speaking, ice is a ‘viscous fluid’, or a ‘non-Newtonian fluid’, which means that its viscosity (or gloopiness) depends on its temperature and how much pressure it is under; the greater the pressure and the warmer the ice, the gloopier it becomes, and the more its crystals squash or ‘deform’. Glaciers grow ever-deeper over time as snow accumulates, and compression plus a little melting and refreezing turn it to ice, after which the crystals start to deform under pressure. By this means, a typical alpine mountain glacier like the Haut Glacier d’Arolla might move just a few metres per year.

All glaciers flow by means of the imperceptible deformation of ice crystals, but they have much quicker ways of moving too. A second means by which glaciers flow involves the glacier sliding over a wet, slippery rock surface. Imagine taking an ice cube from the freezer, placing it on a flat plate, then tilting the plate – the ice cube slides off, right? Now consider the same ice cube on the same tilted surface, but still in the freezer – it’s going nowhere, because the cube is frozen to the plate and there’s no liquid water to lubricate its flow. Small glaciers in the Arctic, where the air is very cold, behave like the frozen ice cube – they don’t slip and slide. They can only move by their ice crystals deforming. But in warmer climes, like the Alps, where the bottoms of glaciers have a thin layer of water, they can slip over their beds – these are called ‘temperate glaciers’.

Even in perishingly cold places like Antarctica, very thick glaciers can curiously still have liquid water at their beds. Imagine blowing up our ice cube to monstrous proportions, the size of a skyscraper hundreds of metres in height, but still keeping it in a freezer. (It’s a very large freezer!) Will it move if you tilt the surface? Actually, it might. Remember that old physics experiment where you hold a cheese wire across a block of ice, then apply pressure to the ice through the wire? The pressure lowers the melting point of the ice, and the wire slices down through it. Thus, our gigantic ice cube – a bit like the Antarctic Ice Sheet – will probably melt at its base due to the huge pressure of the overlying ice. Then, if by some superhuman feat you manage to tilt the surface upon which it rests, it will start to slide – in the wonderful world of glaciology, this is called basal sliding.

A glacier has a third ingenious way to flow if it rests on top of wet mud (or sediment, as a glaciologist would probably call it). Imagine that we now slid a tray of very wet soil collected from the garden just after a heavy rainstorm beneath our vast ice cube in the outsize freezer. What happens next? Well, the pressure of all that ice pressing down on the wet soil causes the water in its tiny pore spaces to become pressurized, which lowers the friction between the soil grains. This makes the soil weak and easy to deform, so if you tilt the tray, the soil will move like a mudslide downhill. The ice cube rides majestically on top of this moving platform of wet, deforming mud. This mechanism of ice flow is known as sediment deformation.

So, ice deforms, ice slides, sediments beneath the glacier deform – that’s three ways glaciers can flow. Putting it in human terms, some glaciers crawl (ice deformation only), other glaciers walk (ice deformation and basal sliding), and a few virtually sprint as ice deforms and the glacier slides, perhaps also hitching a ride on top of deforming sediments. Small glaciers in the European Alps can be considered walking glaciers. In an average year the Haut Glacier d’Arolla moves at most ten or so metres in its centre, where the ice is not slowed down by dragging against the rock sidewalls.³ However, the speed of the ice can more than double for brief periods in summer when meltwater crashes to the base of the glacier, pumping at such high pressure that it pushes up against the ice and raises it slightly off its bed, a process called ‘hydraulic jacking’.⁴ What’s common to all glaciers with water at their beds is that the processes controlling much of the glacier’s flow mostly happen in this inhospitable abyss known as the subglacial zone.

The grand purpose of the expedition I was part of was literally to get to the bottom of the Haut Glacier d’Arolla. This compact valley glacier – so described because it neatly inhabits its valley without overflowing it – formed the focus of the Cambridge University-led ‘Arolla Project’, headed up by one of my all-time glaciology heroes, Professor Martin Sharp, with the audacious goal of discovering what lies beneath glaciers by simply going there. In the case of Arolla, this meant somehow passing through one hundred metres of solid, moving ice.

For me, one of the most enthralling things about glaciers is the fact that the place where all the action happens you can neither see nor touch. You are left to imagine the point where the ice ends and the rock begins, and ponder what life could survive such grinding hostility as the glacier moves, picks up and regurgitates boulders, stones and sand. Only when the ice retreats is the evidence revealed, an ornate assemblage of ice-etched, polished rock surfaces, carved melt channels, moulded sediments – traces of a past dark, violent underworld.

You sense a glacier long before you set foot on it – it makes itself known in the sharpness of the air. But first, reaching the front of any glacier (commonly known as its snout or terminus) normally involves a monotonous hike through what is known as the ‘proglacial zone’. Here, a mass of boulders, pebbles, sands and silt present a chaotic scene, parading sediments and rocks regorged by the glacier during cycles of advance and then retreat, like a person who has upped sticks in a hurry, leaving their house in a mess. Only the ribbons of milky rivers and jewels of emerald lakes trapped between moraines offer signs of life in this barren, uneven moonscape. You barely notice much beyond your feet, while dodging holes and other unsavoury features such as sinking mud, which is commonly found in the vicinity of river channels – fine glacially eroded sediments masquerading as waterlogged leg-sucking death traps. If you prod the surface with a pole, it wobbles like a blubbery belly – ‘porker mud’, we called it, a term you won’t find in the glossary of any textbook.

Meanwhile an icy wind increasingly penetrates your lungs; if anything can be both exhilarating and foreboding, this is it. That first tantalizing smell of the ice, that sense of being stroked by its soft, frigid fingers, is a welcome and a warning. This ‘katabatic’ wind (from the Greek word katabasis, meaning ‘descending’) often builds through the day; it results from heavier, ice-cooled air flowing down the glacier to its snout. Such winds are often seen by mountain communities as the spirit of the glacier.⁵ For me, they are a sign to prepare, to put on an extra layer and get ready for a laborious climb up the steep front of the glacier.

If I’m honest, my first sighting of the Haut Glacier d’Arolla was something of an anticlimax. In fact, I wasn’t even sure that it was a glacier, for it was barely distinguishable from its rocky surrounds. Glacier snouts are grubby things, ‘snout’ being an appropriate word here, given that it essentially has its nose buried in mud, rather like a foraging pig. As glaciers move, they pick up sediments and stones from their rocky beds and receive rockfall from their surrounding valley walls, transporting all this debris, then releasing it upon melting in their lower reaches. Since melt is always highest at the snout of a glacier simply because it’s warmer at lower altitude, the release of this grey debris from its icy shroud is fastest here, and consequently mounds of dirt accumulate chaotically at the margins and fronts of glaciers in ridges known as moraines. Glacier snouts might seem motionless and silent, almost dead, but still the ice continues to flow, albeit slowly, only advancing if the glacier as a whole receives more snowfall in a year than it loses through icemelt.

And so I tentatively set foot upon my very first glacier. The front of a glacier is treacherous terrain, often full of holes and cracks caused by the collapse of the roofs of channels which convey meltwater beneath the thinning terminal ice. As far as snouts go, that of the Hau...