Glaciers – ice on the move
Hacking his way up the brittle flanks of Linda Glacier, alpine guide Charlie Hobbs leads his climbing partner towards the summit of Mt Cook, New Zealand’s highest peak. Vast snowfields that lie within the shadow of Cook and its neighbour, Mt Tasman (left, background), are the source of some of this country’s mightiest river of ice.
Thump , Thump—ice-axe, ice-hammer—thump, thump—left foot, right foot—thump, thump—axe, hammer . . .
Each kick of cramponed boot, each jab of ice-axe sends showers of tiny crystals hissing down the slope into the whiteness below. I watch them free-falling over the polished surface until they disappear.
The wall of ice, like stale sugar glace crudely plastered on to the mountain, sprawls out in all directions. Beneath me, it sweeps down some 500 metres to dissolve into the glacier. Ahead, the summit is a stark white wedge that splits the sky.
I am one of three beetles crawling up the flanks of Mt Cook (3755 m). Beside me, Charlie Hobbs, a weathered mountain guide, is hacking his way up the lustrous ice couloir. Roped to him is his client, Aucklander Bruce Mellor.
Some ten hours ago, under the shimmering blackness of the mountain night, we crossed the fissured hollows of the Grand Plateau and began to climb up the Linda Glacier. For long hours before the sunrise our world had shrunk to the small cones of yellow light cast by our head-torches. Around us, the icefall lay like a prehistoric metropolis that had been reduced to rubble.
Seracs (blocks of ice several storeys high) leaned forward at precarious angles. Crevasses, mouths agape, sliced the surface like knife wounds. Bridges, caves, arches, tunnels, spires and towers—every imaginable type of ice sculpture was there, garlanded with icicles and frosted with wind-swept frozen crust.
Thump, thump . . . we chip and scar our way up the glassy wall. Seventeen . . . eighteen . . . nineteen . . . I count the steps. Every twenty brings a blissful rest. Ahead, Charlie climbs with the casual confidence of a taxi driver cruising his favourite suburb. He leads up the entire rope length, hammers a half-metre-long snow-stake into the slope and calls for Bruce to come up.
The summit nears as we make our way along the ice cap. A strong sou’westerly howls over the ridge, forcing us to hug the steep, wizened slope. We reach the summit cornice and can go no further. In its lee we cut a narrow platform: somewhere to rest, to celebrate, to quench the tormenting thirst.
Here, from the top of New Zealand’s highest mountain, I can take in one of the country’s geographic “signatures”: Tasman Glacier, New Zealand’s mightiest river of ice, meandering some 2000 metres below.
The analogy to a river is remarkably accurate. Just like rivers, glaciers move down their valley beds responding to the principles of flow. Like frozen waterfalls, they cataract over steep escarpments, shattering into spectacular icefalls. They rush (relatively speaking) through narrow gorges and splay out across the valley flats.
The degree of turbulence is reflected by the crevasses. Where a glacier takes a sharp turn, flows over an obstacle or joins another stream of ice, the inner forces exert immense pressure on its surface, causing it to crack and open. Further downstream, after overcoming the impediment, the crevasses close up again, healing and smoothing the battered glacial surface.
There are glaciers on almost every continent of our planet, covering over 11 per cent of the land surface, and locking up 90 per cent of aboveground fresh water. Enormous ice sheets, reaching depths of several kilometres, envelop Antarctica, Greenland and Patagonia. Extensive glacial networks cut through the mountains of Alaska and northern Canada, the Himalayas, Andes and European Alps. Isolated rivers of ice swathe equatorial peaks in Africa and even New Guinea. Only Australia supports no permanent ice today, although the evidence of once-powerful glaciers can be found in Tasmania and on Mount Kosciusko.
New Zealand, according to a count done for UNESCO’s World Glacier Inventory, has 3153 glaciers. Except for 18 glaciers encircling the crater of Mount Ruapehu, all are scattered over the Southern Alps, from the Inland Kaikoura Range in the north to southern Fiordland, comprising some 116 square kilometres of ice. The Waimakariri River watershed alone has nearly 50 glaciers, but most of these are just big enough to qualify for the listing, where an area of 0.01 square kilometres (the size of a rugby field) has been set as the lower limit.
The “big three”—Tasman, Fox and Franz Josef—are all within 20 kilometres of each other, with Tasman falling to the east of the Main Divide while Fox and Franz Josef flow to the west.
Tasman Glacier has its sources on the snowy slopes of the Grand Plateau, in the heart of Mount Cook National Park. Its icy stem, 27 kilometres long and an average of 1.6 kilometres across, is fed by numerous tributaries—a vascular system of roots penetrating the surrounding mountains in search of icy nutrients.
Over much of its length, the glacier carries a rough mantle of moraine. From my icy eyrie it looks like the unfinished work of a giant earth-moving contractor defeated by the size of his undertaking. The glacier’s rocky appearance is deceptive, though, for beneath the thin layer of sombre grey gravel the ice is 600 metres thick. The surface debris shields it from direct sun, slowing down the melting. At the snout, still some 200 metres thick, the ice is 500-800 years old. It fell as snow long before Abel Tasman caught his first glimpse of the craggy skyline of the Southern Alps.
When the heavy moisture-laden clouds scud across the Tasman Sea and drop their burden of snow on to the high snowfields, the glacial cycle begins. Soon after the fall, the fresh snow begins its unique transformation into ice. Melted by the scorching mountain sun, re-frozen by the chill of the night, compressed by the weight of each fresh snowfall, the delicate hexagonal flakes re-crystallise into granules the size of sugar grains called firn—literally “old snow.”
As the seasons change and more fresh snow accumulates above, the increasing pressure causes firn crystals to further amalgamate into larger ice crystals, some of which may eventually reach the size of a pumpkin. Initially, the ice is full of trapped air bubbles and is white. As the years go by, the glacier’s internal pressure expels the bubbles and the ice becomes clear blue. (Ice, like water, absorbs all wavelengths of the visible spectrum except blue.) But even before this transformation is complete, under its own weight the apparently solid ice begins to move.
For the most part, the glacier is simply sliding on its rocky bed—oozing along on a lubricating film of water created by localised pressure-induced melting. (The principle is the same as that which allows ice-skaters to slide effortlessly over solid ice.)
A second component of glacier movement happens inside the glacier itself. At great pressures, the molecules within the ice crystals align themselves in parallel planes which can slip over each other. This phenomenon, known as internal deformation, allows the ice to act like very thick porridge.
The movement of ice is endlessly fascinating, both to those who study glaciers and to those who simply admire them. In one waggish episode, Mark Twain, after climbing a modest peak in the Swiss Alps, tried to make novel use of the Gorner Glacier as a “down” escalator, thereby saving himself a tiring journey on foot. Only after having ensconced himself and his climbing party on the ice did he realise that, at the rate of an inch a day, it would take him 500 years to get to his destination.
Twain would have fared better on the Franz Josef, which averages two to three metres per day, but has on occasions clocked an electrifying seven metres per day. On the other side of the Divide, though, the Tasman creeps along at a mere 65 centimetres per day.
Fast or slow, the speed of the ice has nothing to do with whether the glacier as a whole is advancing or retreating—what glaciologists refer to as the glacier’s “health.” That is governed by an intricate and dynamic balance between the accumulation of snow and the melting (ablation) of ice. If accumulation exceeds ablation, the glacier expands and its snout moves down the valley. If more ice melts than the freshly falling snow can replenish, the glacier thins out and its snout recedes, leaving behind stranded rock debris and a scoured landscape. (See box, page 63.)
The fact that glaciers move at all is of enormous importance to the planet. If they did not, then most of the earth’s moisture would become permanently trapped in vast mountains of ice, and would never fall as rain. The world would be a desert.
As well as being a powerful determinant of global weather (and, in turn, reflecting climate change), glaciers have a profound effect on landscapes, grinding down mountains and redistributing their wealth of minerals over vast areas of land.
However, not all glacial influences are benign. It was a piece of glacier (all icebergs originate from glaciers) which sank the Titanic. In 1962, a glacier on Mt Huascaran in the Peruvian Andes triggered an avalanche which engulfed nine villages and took 4000 lives. At its peak, the avalanche travelled at 100 kph and pushed before it a 50-metre-high wall of debris.
The threat of avalanche or falling ice is continually in the minds of mountaineers. Everest’s treacherous Khumbu Icefall, negotiated by Sir Edmund Hillary on his pioneering ascent, has claimed many lives, and there have been deaths on New Zealand glaciers, too.
On a cloudless February day in 1914, three men were crossing the upper Linda Glacier after a successful ascent of Mt Cook. Sydney King, a visiting English climber, walked in the middle of the trio, flanked by two guides, Darby Thomson and Jock Richmond.
They had spent three mesmerising hours on the summit, and their minds raced ahead to the Haast Ridge camp. There would be mugs of steaming tea and a long-awaited hot meal. Wrapped in sleeping bags, they would sit outside their tent, facing the vista of endless mountains, and savour their pipe tobacco and the fleeting moment of peace that can only be felt by a climber who has just accomplished his goal, and whose restless mind has yet to fix on the next challenge.
Heat poured from the summer sky, turning the snow into something with the consistency of mashed potatoes. The men plodded patiently in the knee-deep slush, silent among the silent mountains.
Then, a muffled groan of splitting ice, and the glacier above them suddenly comes to life. It seems as if the entire icefall is coming down to meet them.
“Run! Run!” cries Darby, and with giant strides races towards the nearby rocks. The others follow. One man stumbles, but the pulling rope keeps him upright.
With every step the snow seems to grip their feet more firmly, stealing precious seconds. They wheeze in the rarefied air, but are numb to pain. A few more steps and they will reach the lee of the Bowie Ridge, and safety.
The avalanche catches them, sweeping them down the glacier in a rumbling fury of ice, killing them instantly.
Only the body of Jock Richmond is exhumed from the rubble by the search party. Sydney King’s body is never found, and the mauled remains of Darby Thomson surface 14 years later at the bottom of the Hochstetter Icefall, some 1500 vertical metres from where the avalanche came to a halt.
Most avalanches leave no lasting sign of their presence. Even the massive cascade of ice and rock which, in 1991, stripped ten metres off the height of Mt Cook (see New Zealand Geographic, Issue 13) is being swallowed by the surrounding terrain. Glaciers, acting as nature’s conveyor belts, distribute the debris, and fresh snowfalls repaint the landscape. Soon, time will have healed even the scar on Cook’s east face where the avalanche occurred.
At night, as you look across the Grand Plateau and see the serrated silhouette of the mountains of the Main Divide engraved against the Milky Way, the stillness is beyond time. The landscape seems unchanged since the titanic confrontation between Indo-Australian and Pacific tectonic plates thrust the ranges into the sky some three million years ago.
Yet this realm of rock and ice is anything but still, for ever since their birth the mountains have been rising at a rate of about six millimetres per year. If not for the eroding, rasping power of the glaciers, which shear the new growth at almost the same speed, Mount Cook would be 18 kilometres high by now, and you could see it from the moon.
For some 64 km, from the twin-peaked pyramid of Elie de Beaumont to the rocky summit of Mt Isabel rising above the Mueller Glacier, the Divide becomes the border between two of our most heavily glaciated national parks. To the east, Mount Cook National Park stretches over 70011 hectares, 40 per cent of which is under permanent ice and snow. On the other side, Westland National Park has 60 named glaciers strewn over 88680 ha of mostly untouched hinterland.
In 1991, both parks became part of the South-West New Zealand World Heritage Park, and were declared an “outstanding example representing the major stages of Earth’s evolutionary history.”
Although the glittering peaks of Southern Alps were noted by Tasman, Cook and Stokes during their voyages of discovery, the main West Coast glaciers—Fox and Franz Josef—were not mentioned until the vessel Mary Louisa sailed along the coast in 1859.
An entry in the ship’s log book for June 14 reads: “We saw what appeared to be a streak of mist running from between two peaks. . . At noon, abreast Mount Cook, close inshore, we could see distinctly that it was an immense field of ice, entirely filling up the valley.”
The larger of the two glaciers was known to the early Maori inhabitants of the Poutini Coast as KaRoimata-O-Hine-Hukatere, the tears of the avalanche girl. Legend has it that an adventurous Maori woman, Hine-Hukatere, who often ventured into the mysterious world of towering mountains and glittering snow-fields, once persuaded her lover, Tawe, to accompany her on one of these escapades. As they climbed near the great peaks of the Main Divide, Tawe, lacking confidence in this unforgiving terrain, slipped and plunged to his death at the foot of the mountains. Hine cried out her grief, and her endless tears flowing towards the distant sea were frozen by the condoling gods into a stream of ice.
In 1864, Julius von Haast, Prussian-born provincial geologist of Canterbury, visited the glacier, renaming it after Austro-Hungarian Emperor Franz Josef.
At that time, the ice terminus pressed hard against Sentinel Rock, a 282-metre high outcrop known as a roche moutonnee, which had survived the onslaughts of previous glaciations. For most of the following hundred years, despite several minor re-advances, the snout of the glacier has receded some three kilometres. In 1983, a year with a markedly El Nino weather pattern, the recession stopped suddenly, and since then the glacier has been rapidly advancing.
When I first visited Franz Josef Glacier, in February 1993, its snout was 15 metres short of the viewing gallery, a wooden barrier perched on ice-polished rock. A looming wall of bulging, broken-up ice—characteristic of advancing glaciers—hung over the valley floor. Long ice pinnacles, reaching the crest of the wall, toppled over like soldiers in a firing line. It was a spectacle of crushed ice, falling rocks and burbling water accompanied by groans and grunts from the bowels of the icy beast.
Several weeks later, the snout reached the rock, pushed against it, stopped temporarily, and began building up in height and volume. The viewing gallery had to be moved 70 metres downhill; the glacier was reclaiming its ancient territory.
The neves of Franz Josef and Fox glaciers have one of the highest precipitation levels in the world. Annual rainfall can be as much as 15 metres in this region, and in the mountains one metre of rain equates to about three metres of snow.
This, coupled with the fact that the valleys on the western side of the Divide are narrow and steep, means that these glaciers move like greased lightning, compared with most.
At times, Franz Josef Glacier has been a troublesome neighbour for the small community which lives in its valley. In December 1965, after heavy rainfall (280 mm in two days) the glacier became so saturated with water that its snout burst like an overpressurised dam.
Ice and rock shrapnel showered the valley and the neighbouring forest. The unleashed river surged towards the sea, carrying chunks of ice that were still half a metre across when they met the foamy West Coast breakers some 20 kilometres away.
During a similar event in April 1991, the collapsing terminal face sent a tsunami-like shock-wave sweeping along the valley. The Waiho bridge survived the onslaught, but it was yet another reminder to the residents of Franz Josef not to take the glacier for granted.
Long-time glacier guide Peter McCormack shows me where hanging galleries were once strung across the smooth rock slabs in the never-ending battle for tourist access to the ice. Today they have all rotted away. Only ochre-brown patches of rust around the weathered bolts recall the fleeting architectural glories of long ago.
“This track here used to be a road.” Peter points at a path that cuts through a gorge made of house-size rocks. “In the ’50s we could drive right up to the snout. Now the road is under 30 feet of gravel.”
Among the floods and avalanches caused by the glacier, one has been welcomed: the flood of tourists. Nowhere else in the world are the advancing glaciers as easily accessible as on the West Coast, and as the word has spread, Fox and Franz Josef have turned into bustling boom-towns.
Their main streets have all but disappeared behind a facade of billboards advertising glacier tours, scenic flights, restaurants, motels and shops. A helicopter pilot can clock up 30 flights on a long summer day; he leaves the engine idling even during refuelling.
I take the short flight up the Franz Josef to join a Department of Conservation maintenance party. Their task is to renovate the historic Almer Hut, which hunkers on a ridge of broken rock above the winding stream of ice, only a stone’s throw from the place where Charlie Douglas and Arthur Harper built their temporary shelter during the first systematic mapping of the glacier in 1893.
It is summer, so the glacier ice is more fragmented than it is during winter. The reason for this is that glacier ice has a small amount of salt in it, originally picked up from evaporation over the sea. The salt accumulates at the edges of the ice crystals, and because salty ice melts more quickly than pure ice, warm summer days encourage the crystals to separate from each other. In winter there is less melting and the surface of the glacier is slicker and more slippery.
High above the hut and beyond the terraced jumble of the icefalls are the accumulation snow-fields of the glacier. Covering an area roughly the size of Greater Auckland, they consist of three distinct neves: Geikie, Chamberlin and Davis Snowfields.
The latter two feed the Agassiz Glacier, one of the larger tributaries of the Franz Josef. It was named after Louis Agassiz, a 19th century Swiss scientist, who besides being a world expert on fish fossils, proposed the revolutionary theory that “epochs of intense cold”—ice ages—had at one time prevailed on the earth.
It was a brave theory for its time (1837), for the Antarctic Ice Sheet had not yet been discovered, and the idea of ice-fields covering entire continents seemed almost unimaginable. The traditional explanation for such geological curiosities as erratic boulders found hundreds of kilometres away from their original rock-beds was that of the biblical Flood, and even Agassiz’s long-time mentor and friend, the German naturalist Alexander von Humboldt, did not support the young scientist.
But Agassiz persisted, and, sponsored by the King of Prussia, soon established the first glacial research station on the Unteraare Glacier, 40 kilometres south-east of Bern.
His activities were not confined to mere academic discussion and scholarly analysis. For ten years he scaled the highest mountains of the European Alps and travelled across the glaciers which surrounded them. He was the first scientist to be lowered into a glacial crevasse to its water-filled bottom at a depth of over 30 metres. After a harrowing ride back to the surface, during which he narrowly escaped being skewered by needle-sharp stalactites, he wrote: “I should not advise anyone to follow my example.”
His research convinced his contemporaries that he was right about ice ages and glacial movement. A new science, glaciology, was born, and enthusiastic researchers around the world began cheerfully disregarding Agassiz’s advice, enduring alpine privations to discover the secrets of moving ice.
As the main Divide veers southwards, the glaciers become smaller and more scattered, crowning only the loftiest peaks and mountain ranges, until again they burst into a spectacular display of power and primeval beauty in the icy wonderland of Mount Aspiring National Park.
Aspiring, known to Maori as Tititea, the glittering peak, is surrounded by three mighty glaciers: Therma, Bonar and the terraced system of Upper and Lower Volta. These large cirques of ice ceaselessly chafe away at the soft, flaky sides of the mountain, scooping out deep basins and shaping sharp, pinnacled ridges. The 3027-metre summit is a culmination of four of these ridges, whose jagged crests give the mountain its pyramid-like appearance.
Here, in the company of a heavily laden climbing party, I spend a fruitless week in a tiny mountain hut, playing a waiting game with the weather.
Day after day, squalls of unremitting rain, sleet and later snow lash our tiny shelter with the strength of a hurricane and the persistence of a monsoon. Hooting wind plays a wild pizzicato on the guy-wires anchoring the hut, and at times it seems as if our quivering refuge could become air-borne.
Time passes slowly, measured by irregular meals and evening schedules of the Mountain Radio. Nightly weather forecasts are persistently grim:
“A low centred over the Tasman Sea is expected to move across the South Island tomorrow,” the methodical, emotionless voice reads. Reception is poor, and the words come in snatches. “Strong northwesterly winds increasing to gale force around the tops . . . freezing level 3200 metres, rising to 4000 metres . . . estimated precipitation 200 mm of rain .. . calling .. . GX 401 . . . do you copy, over . . .”
One by one, distant voices come through the crackles and hisses, reporting their location and activities. Somebody is in remote Kaipo Valley in Fiordland. Someone else is just finishing a survey of the Godley Glacier. The entire Southern Alps is engulfed in a violent storm, and weather is the theme of the day.
We are not the first to be hutbound here, nor is the severity of the storm unusual. I find an earlier entry in the hut book: “Another stormy day. I can only assume that the but mouse died of boredom.”
After seven days of waiting, with food and fuel stretched to the limits, we abandon our climbing plans and decide to return to the lowlands. Taking advantage of a brief lull in the storm, four of us rope up and begin to navigate our way through the labyrinth of crevasses.
Glacier crevasses range from knife-thin fractures to several-metrewide rifts. But it’s not the crevasses which you see that are dangerous; it’s the ones you can’t see. The strong winds which often sweep the glaciers build large snow cornices on both lips of a crevasse. These, if large enough, can bridge and ultimately cover the crevasse.
During the night and early morning, when the penetrating frost congeals the snow into a concrete-hard mantle, snow-bridges can provide a safe way of crossing a crevassed glacier. Later in the day, as the temperature rises, they become soft and unstable, often collapsing under the weight of a climber.
But where are the crevasses now? For as far as the eye can see, the glacier is a soft, velvet-smooth plain, fading seamlessly into the thick candyfloss of pewter clouds. The long westerly storm, a forerunner of incoming winter, has draped the ice with a fluffy blanket of the fresh snow, concealing its dangers and making travelling across it slow and perilous.
Probing my way ahead with the ice-axe, I try to anticipate possible lines of weakness. Each step is like a chance in a Russian roulette of solid and soft, safe and treacherous. Eyes desperately scan the white pall for clues. Sometimes it is an inconspicuous dent in the snow, sometimes a thin crack, sometimes . . .
With a muffled crunch the snow gives way and both my feet break through a thin bridge. I fall up to my waist, but my pack catches on the snow and holds me.
Out of the corner of my eye I see my companions dropping flat on the ground, bracing on their ice-axes.
With my feet dangling in empty space, I probe the snow around me, looking for some terra firma, but each time the shaft of the ice-axe pierces the snow crust into hollowness. I lean forwards to spread my weight over the widest possible surface, then, stretching into a star shape, I manage to worm my way to safer ground.
Too close for comfort, I think. The others agree. Defeated by deteriorating visibility and our slow progress, we retrace our footsteps to the hut.
The following day, the glacier has changed its appearance completely. A southerly wind, bringing cold Antarctic air, has swept across the ice, freezing it solid. The snow-bridges, reinforced by frost, are no longer deadly traps, but displays of nature’s beauty, enchanting and mysterious. In the heat of the afternoon sun their dark-blue cavities echo the delicate murmur of streams trickling inside the glacier. We travel with ease.
In the days before time, there was a great monolith of rock stretching south from what today is Milford Sound to the sea-battered bluffs of Puysegur Point. It was a part of the upturned and sunken canoe of Aoraki that became the South Island, Te Wahi Pounamu.
Wise and benevolent god Tu-TeRaki-Whanoa, who was given the task of putting final touches to the newly created island, decided to break the monotony of the rocky coast. Time after time his gigantic axe cut deeply into the solid rock, and with each blow this Polynesian Hercules, chanting a powerful invocation, heaved on the shaft to make the splits wider. As he worked his way along the coast, the sea-water entered the roughly chopped gorges and they became fiords.
Nowadays, we have a more pragmatic, if somewhat less colourful, explanation of how the great fiords came to be. Fourteen thousand years ago, when large flocks of moa roamed the lowland forests, Fiordland was almost entirely engulfed by ice, often as much as 1400 metres thick. Individual ice streams joined together until only the tops of the highest mountains pierced its frozen surface—a scattering of lonely islands stretched across the glittering whiteness.
To the east, the ice sprawled freely from the valleys, and joined to form a large ice sheet known as a piedmont glacier. Its spread was finally stopped by the arid plains of Otago. In the west, on reaching the sea, the glaciers terminated in steep, partially floating ice-cliffs which strewed the coast with a clotted barrier of drifting icebergs.
Subsequent warming of the world’s climate by some 4-6°C brought an end to the ice age, and, like gigantic snails, the glaciers withdrew into their high alpine shells, revealing a heavily scarred and reshaped land. They left a legacy of razor-sharp rock ridges and spires, basin-shaped valleys, hillocky moraines, lakes and roches moutonnees, but, most of all, in deeply carved U-shaped canyons that once carried vast streams of ice.
Between 9500 and 8000 years ago, nourished by the melting ice, the sea rose some 100 metres, flooding the valleys, and when its level stabilised (by about 6500 years before the present), the fiords remained. And, whereas in other parts of the Southern Alps erosion has concealed the evidence of the glacial past, here the hard plutonic rocks have preserved it in an almost unchanged form.
Today, all the remaining glaciers of Fiordland—Pembroke, Donne and Ngapunatoru Ice Plateau, to name the largest—are confined to relatively inaccessible areas of the Darran Mountains. They have become miniatures of their powerful predecessors—isolated patches of ice precariously clinging to the mountain-tops, overlooking the gloomy fiords they once created.
The Task of researching and surveying glaciers has tended to attract people who are scientists by vocation and mountaineers and explorers by passion.
One of them was T. N. Brodrick, district surveyor for South Canterbury, who in 1889 began mapping the glaciers of the Mount Cook area. By planting lines of stakes across Tasman, Murchison and Hooker, and resurveying their positions in following months, he was able to determine the speed of ice movement and to plot the first cross-section of Tasman Glacier.
At that time, revitalised by the Little Ice Age (which saw a worldwide advance of ice between 1600 and 1830), the glacier was in its prime. Since then it has thinned out dramatically, losing on average half a per cent of its volume (or 46 million cubic metres) every year.
The person who takes the ice’s pulse today—and the country’s leading glaciologist—is Trevor Chinn. Born on the West Coast at Te Taho, on the edge of a glacier outwash plain and under the shadow of Mt Adams, it was perhaps inevitable that he should develop a passion for the alpine world.
In mid-April, I returned to Mount Cook village with Trevor to meet a group of UK scientists and students who were measuring the position of the ice surface on Tasman Glacier.
“We chose the Tasman because of its size and relative accessibility,” shouts team leader David Feltham over the whining engine of a truck which is bouncing along the Ball Hut road. “There are not many places in the world where you can drive up to a glacier of this size. It makes our logistics much easier.”
Why is it, I wondered, that after years of only sporadic interest in our glaciers, they have suddenly become a centre of attention for the international scientific community?
“A glacier is a giant meteorological instrument, more sensitive to climate changes than anything else we know,” Trevor Chinn tells me as we walk across the upper neve of the glacier. “If we can find a link between a glacier’s size and temperature-precipitation patterns, we may be able to predict future global climate changes.”
Global sea level fluctuations, too. Scientists estimate that if all of the world’s ice were to melt (which would take several hundred if not thousand years), the sea level would rise by over 80 metres, and much of the land, including heavily populated coasts and vast arable plains, would disappear underwater. In New Zealand, the ocean would lap against the foothills of the Southern Alps, and Auckland would turn into an archipelago of semi-submerged volcanic cones. Such a scenario is unlikely, of course, but even a one-metre rise would have disastrous consequences worldwide.
Since glacier measurements were first taken in the late 1800s, all of New Zealand glaciers, responding to the global warming trend, have shrunk. From the early 1980s, however, there has been a trend towards positive snow balances.
Some glaciers, like Franz Josef and Fox, have responded quickly, advancing down their ancient valleys or doubling the thickness of their terminal faces. Others, like Tasman or Murchison, have absorbed the heavy snowfalls, but, because of their slow response time, it may be many years before we see any significant advance or thickening.
As we cross the neve, Trevor is looking for a freshly open crevasse, in order to measure the snowfall of the last three years. Many crevasses are covered by a drift of fresh snow, but eventually we find one below the slopes of Mount Almer.
Using a snow stake and ice-axe as anchors, I set up a rope for abseiling into the crevasse. Attaching his descender, Trevor throws the free end of the rope into the gaping crack and, with an impish twinkle in his eye, disappears over the edge.
Newly open crevasses, unaltered by rain, melting or movement of ice, provide a unique opportunity to study a glacier’s anatomy. During summer, wind-blown particles of dust and pollen settle on the melting surface of the white winter snow, creating a distinct dark layer. Next winter’s snow produces a fresh white layer, and so the process continues, resulting in a zebra-like pattern of parallel bands which becomes clearly visible as the crevasse begins to open.
I wait until the rope is free, and follow Trevor into the abyss. Ten metres below the surface there is a wide, sloping snow-bridge—a cushioned catwalk frost-welded across the crevasse. Further down, its airy cleft curves away into the gloom.
The walls of the crevasse are vertical, and abseiling down is like travelling through time.
“This is the summer of 1992,” Trevor says, pointing at a darker band. “And this,” he draws the pick of his ice-axe along a thin, glassy layer in the middle of the 1992 winter band, “is what’s left of a southerly storm.”
The deeper you go, the thinner the winter-summer layers become, but they still retain their frozen records. By drilling into the glacier and retrieving and analysing the ice cores, scientists have been able to leaf through large chapters of the book of Earth’s history.
“In dry glaciers, such as those of the Antarctic Ice Sheet, where the arid, cold climate has kept the strata well preserved, we can go back 300,000 years, through ice ages and interglacials,” says Trevor. “Analysing the core—which can be a mile long—we can determine the gas and dust content of the atmosphere, and the air temperature. All the major geological events like eruptions of volcanoes or meteorite collisions are well documented in the ice.”
Absorbed by our time travel, written on the glittering walls of the crevasse, we have forgotten about the present. When we return to the surface, the sky is on fire, flaming in yellow, red and crimson. Then the night creeps in, extinguishing another Pinatubo sunset.
On June 15, 1991, a powerful volcano on Luzon, the largest island of the Philippine archipelago, awoke from its 600-year dormancy into violent eruption. Mount Pinatubo’s deep, narrow vent, like an underground gun-barrel, sent an estimated 15 million tons of fine dust high into the stratosphere. There, above the level of the rain clouds, dust can remain for several years before it eventually succumbs to the Earth’s gravitational force.
Spilling over both hemispheres, this billow of debris scattered and absorbed some of the sun’s heat radiation, reducing it by as much as five per cent. The dust also influenced prevailing weather patterns, causing a temporary drop in world average temperatures of between one and two degrees. The long-term effects are yet to be seen.
Whether Pinatubo is responsible or not, the snows have come to Mount Cook early this year. The summer tourist season has ended, and the winter skiing has not yet begun. The scientists have left, taking with them an abundance of new data, stacks of equipment and leftover provisions. Life in Mount Cook village has changed into a slower gear, and the mountains have been left to themselves.
The glaciers have changed, too. Winter has wrapped them in a robe of fresh snow, filling up crevasses, concealing rocks and moraines and the sprinkling of summer dust. It is the beginning of the time of plenty, the time of nourishment and of hoarding reserves of snow and ice for the year to come.
Under a sickle-sharp crescent moon I ski across the Tasman neve,leaving behind a squiggle of tracks—a crude stitching across the flawless white plain. In a velvet silence cleaved only by the rhythmic swooshing of skis, feathery snowflakes begin to fall. Shyly at first, they soon thicken into a gauzy curtain, erasing any sense of direction, gradient and time.
Unfailingly, the winter has arrived and with it the beginning of a new glacial cycle.
Even with today’s sophisticated surveying and meteorological equipment, scientists cannot predict what will happen to our glaciers. If global warming continues—and many believe it will—they may all disappear within the next few hundred years, leaving only isolated patches of ice atop the highest mountains, like Ruapehu and Taranaki.
Or perhaps the heavy snowfalls and low temperatures of recent years are not just a combined effect of El Nino and the Pinatubo eruption—a short-lived interlude of glacial advance in a long-term retreat. Perhaps it is the beginning of another “epoch of immense cold,” an epoch of powerful glaciers merging into a vast ice sheet, overriding their ancient moraines, breaking off into the sea, festooning the coastline with icebergs.
“We are probably living at the end of an interglacial, a warm period between two glacials,” Trevor Chinn told me. “If our calculations are correct, we are long overdue for another ice age.”
Ice ages have come and gone throughout the history of the world. Each one has had numerous cool glaciations separated by warmer interglacial periods. All it would take is a four-degree drop below today’s average temperature and we would plunge back into the “deep freeze.”
The glacial book of the Earth’s history is unfinished. We have glimpsed the past by leafing through the preceding chapters; their fine-print will keep the scientists busy for many years. Future pages are blank, and we, the readers, can only speculate about what is to come.