Tambora: The Eruption That Changed the World (25 page)

One imagines Perraudin teasing Venetz’s curiosity with the heretical image of vast Alpine ice sheets as they clambered up Mount Le Pleureur toward the Giétro glacier in the spring of 1818. Perhaps Perraudin knew that Venetz, in addition to his day job as engineer of Valais, was an amateur naturalist with a specific interest in glaciers and had given a
paper two years earlier before the Swiss Society of Natural Sciences on the subject of glacial advance and the transport of debris. This early paper had made no mention of large-scale glaciation, however, and did not challenge the established theory that the geological features of the Alps had been caused by aquatic submersion—by the very sort of catastrophic flood that now threatened the Val de Bagnes.

No doubt Jean de Charpentier would have listened in to the conversation and expressed his doubts. But Perraudin was persistent by nature and had reason on his side. How could these rocks be scarred, those moraines have formed, or these boulders have been transported miles from their place of origin except by the powers of glaciation? No flood could engineer earth removal at such a scale. One can imagine Charpentier and Venetz looking at each other and shaking their heads. Perhaps Perraudin’s status as an uneducated peasant made it all the more difficult to accept what was, for the time, a truly outlandish notion.

But Perraudin had done his job. The seed of Ice Age theory was planted. It had crossed the threshold separating folk belief and educated, scientific opinion, and though it would take decades to emerge fully formed, the logic of glaciation was now as unstoppable as the mighty lake forming behind the ice dam on the River Dranse. These three Swiss men—Venetz, Perraudin, and Charpentier—represent a who’s who of early glacial theory, and thus modern climate science. Their happenstance gathering in the mountains above the Val de Bagnes in spring 1818, however it precisely occurred, marks the first dynamic concatenation of glacialist ideas that would ultimately lead to the establishment of Ice Age theory. It was the explosion of a faraway mountain, Tambora, that first brought them together as a group to tackle one of that volcanic event’s many spin-off threats, in this case an Alpine
jökulhlaup
.

What Venetz found on arrival at the gorge appalled him. For this vast dammed lake to empty itself into the Val de Bagnes was to imagine a debacle of truly biblical proportions. But with energy and ingenuity to burn—and deep pockets for payment of danger money to his workers—Venetz set about averting the crisis. First of all, he ordered
the cutting of a tunnel through the giant cone-shaped ice wall in the hope of managing the gradual release of water from the dam. This task was carried out under the intermittent hail of enormous blocks of ice breaking from the glacier overhead, which sent large waves over the top of the wall of ice. Added to that was the ever-present, stomach-churning threat that the dam itself might suddenly give way, sweeping the entire party to their deaths in a calamitous torrent.

Making the situation more difficult still, the weather was terrible. Tambora was not yet done with the Alps. After two feet of snow fell in two days in mid-May, most of the workers quit in protest at the freezing conditions. They worked night and day, hacking at the ice with hatchets while soaked in icy water, wearing ordinary shoes instead of waterproof boots. Venetz sent the demoralized Italians home and lured his toughest Swiss montagnards back with the promise of bonuses. Work continued around the clock for a month as the water level of the dam continued to rise ominously toward the foot of the tunnel. Venetz himself camped out on the ice. Would the ice wall hold long enough for the tunnel to work its draining effect? Several false alarms led to premature evacuations of the valley. And when, on the evening of June 13, water began to issue through Venetz’s tunnel, the state of high alert across the valley began to relax. Three days later, the water level of the dam had dropped by ten meters. By the time the dam ultimately burst, Venetz’s tunnel had reduced its volume by a full third, sparing the valley a worse calamity.

Because Venetz could not quite save the day. The water coursing through the tunnel, combined with that continually cascading from the Giétro glacier above and through myriad other cracks in the ice, dramatically reduced the thickness of the wall until finally, at 4:30 in the afternoon of June 16, the frozen edifice suddenly collapsed with an enormous, deafening crash. Fifteen million cubic meters of heaving water, ice, and mud thundered down into the Val de Bagnes. Venetz and his workers scrambled to higher ground and watched in horror as the pent-up River Dranse, now a hundred-foot-high tsunami, rushed through the gorge, dragging boulders and great blocks of glacial ice with it before launching itself with a roar into the valley. The old stone
bridge at Lake Mauvoisin was smashed in an instant. Dozens of hillside chalets fell victim to the great onrushing tide, while in the valley farmhouses and barns bobbed on the torrent like giant toys. The flood ripped entire forests from their roots, as glossy orchards and fields of wheat and grain were submerged, including the family farmlands of Jean-Pierre Perraudin.

By the time it reached the plain, the flood had assumed a truly sinister character: an oozing lake of black mud filled with rocks and tree trunks churned toward the River Rhône at Martigny, accompanied by a thick, black fog. Vital infrastructure and industries of the valley—roads, bridges, sawmills, flour mills, and an ironworks—sank beneath the miasma. In the words of one eyewitness the entire valley, “but a moment before so beautiful and so populous, was converted in a moment into a dreary desert.”
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In Martigny, this wall of mud, ice, and dangerous debris flooded the streets and houses, reaching up to the second story.

The icy deluge took half an hour to pass. It spilled across the River Rhône, and only exhausted its destructive rage on reaching Lake Geneva around midnight, into whose vast depths it was finally absorbed. It left behind a sixty-kilometer plain of utter devastation, filled with thick mud, the detritus of houses and furniture, piled-up ice, rocks, and vegetation, and, inevitably, the corpses of men, women, and thousands of animals. Lulled by the apparent success of Venetz’s tunnel, the early alarm system in the valley had failed, giving the remaining residents minutes rather than hours to escape. Most villagers had already relocated into the hills, however, and so the human tragedy was not on the scale it might have been. Venetz’s brilliant, brave engineering on the dam had certainly saved Martigny, the largest town in the valley, from total destruction.

Nevertheless, the impacts of the Giétro debacle were devastating enough. A full decade after the event, an English travel writer named William Brockedon was struck by the wholesale “desolation and dulness” he encountered in the Val de Bagnes, especially as compared to the picturesque beauty of the neighboring valleys. Ascending the paths that crisscrossed the now becalmed River Dranse, he came across the ruins of a stone house, which stood like “an object of malediction,” and
symbolized “the desolate and ruined state of the valley.” He itemized the geological changes wrought by the 1818 debacle:

Vast blocks of stone, which were driven and deposited there by the force of that inundation, strew the valley, and sand and pebbles present an arid surface where rich pasturages were seen before the catastrophe. The quantity of the water suddenly discharged … and the velocity of its descent, is a measure of force which it is difficult to conceive.
²⁰

Another literally earth-shattering event, and another moonscape—courtesy of faraway Tambora. Ironically, despite this long-term devastation of the valley, Venetz’s success in moderating the flood and ensuring a low death toll meant that his renown would remain local. The 1818 inundation of the Val de Bagnes occupies only a modest place in the rank of nineteenth-century European catastrophes, a relatively minor instance of the global tsunami of ecological consequences flowing from Tambora’s 1815 eruption. As a turning point in the history of geology and climate science, however, the Giétro debacle assumes epochal proportions. The geological impact of the flood impressed Ignace Venetz as proof positive of far deeper historical processes in the Alps. These processes in turn demanded an entirely new kind of science—one founded on the concept and historical reality of climate change.

A CATASTROPHE, BUT NOT CATASTROPHISM

Now largely forgotten outside Switzerland, the 1818 Val de Bagnes disaster was nevertheless widely reported in the European press and became a major talking point in scientific circles. For those whose information came only from reading reports of the deluge, the event appeared to support the conventional catastrophist theories of geological formation, which, influenced by the biblical account, emphasized the shaping power of a great flood or floods that had once submerged the continent and carved out its valleys and mountains. This catastrophic diluvian scenario purported to explain the transport of erratic boulders far from
their original location, as well as the thread of moraines at sometimes great distances from the current location of Alpine glaciers.

From a distance, the bursting of the River Dranse dam offered a very useful simulation of large-scale flooding, a kind of test case for catastrophism. Moreover, a selective sketch of the results proved highly reassuring to catastrophists. High above the valley floor, the Dranse flood had left new lines of debris that corresponded well with the character of ancient moraines. In addition, its tidal power had detached large boulders from the mountainsides and dumped them at great distances along the valley. One such block was measured at forty cubic meters, which, while still only one-tenth the size of the massive Pierre à Bot, the most celebrated of the Alpine erratics, seemed to confirm the transportive power of a massive torrent of water and mud, and to eliminate the need for any alternative geological explanation.
²¹

Such, at least, was the general consensus surrounding the Val de Bagnes debacle. But the closest expert witness to the event, Ignace Venetz, was not convinced. His experience of the catastrophic flood of 1818 brought him, instead, to the diametrically opposite conclusion: only glaciers had the power to form the Alps. Two years earlier, he had delivered a paper that conformed to a traditional theory of erratic boulders transported by rolling on top of glaciers. By 1821, he had developed the outlines of modern glacial theory and periodic Ice Ages. In between, he met Jean-Pierre Perraudin and witnessed firsthand the catastrophic flood of the Val de Bagnes.

Venetz was a brilliantly intuitive geologist but, unfortunately, not a prolific or confident writer. His 1821 prize-winning paper to the Swiss Society is a rambling amateur affair, immersed in details, but its bullet-point conclusions sketch out, in bold terms, the basic principles of modern climate science. Glaciers were nature’s own antique ruins, the “relics of former climates.”
²²
“The moraines found at a significant distance from the glaciers,” Venetz writes, “date from a period lost in the mists of time.” Therefore, by a simple but crucial step of logic, he must infer that “temperature rises and falls periodically, though in an irregular cycle.”
²³
Climate change, Venetz concludes, has driven an historical cycle of glaciation, which in turn has left its indelible mark on the geological
formation of the Alps and by implication the European continent. Amazingly, Venetz’s historic 1821 paper was not published for another twelve years, by which time Jean de Charpentier, after his own protracted period of doubtful rumination, had taken up the cause. After seeing to the publication of Venetz’s paper, he promoted its conclusions in a far more widely read article of his own published in 1834, at which point the new glacial theory came to the attention of the new head of the Swiss Society, Charpentier’s onetime protégé Louis Agassiz.
²⁴

We can wonder at how the course of nineteenth-century science might have been different had Venetz possessed skills of argument and self-promotion equal to his resourcefulness as an engineer and geological theorist. But rarely does such a combination of talents reside with one individual. More curious, therefore, and more profitable, is to speculate upon how it was that Venetz was converted to the radical glacialist theories of Jean-Pierre Perraudin in the aftermath of the Val de Bagnes deluge, when so many other observers saw in that event only a confirmation of the received wisdom—that a diluvian catastrophe had shaped the geological history of the Alps. On what grounds did Venetz come to the opposite conclusion and thus initiate the slow march toward the scientific truth of glaciation?

Where casual or more distant observers had seen proof of diluvian theory, Venetz had the benefit of close examination of the gorge and hillsides of the Val de Bagnes impacted by the violent deluge. There he found no new striations on the surface of rocks. While it was true the rushing tide of water had left moraine-like lines of debris at high elevation and had displaced rocks in large quantities, neither of these actions was on a scale to allow him to persist in the belief that water or mud alone could have been the agent of Alpine formation. With flooding eliminated, only a theory of glacial transport remained.

Though Venetz left no detailed account of the progress of his discoveries, there must have been a day, in 1819 or 1820, when his thoughts returned to his dramatic summer in the Val de Bagnes. There, amid all the pressures of the dam crisis on the River Dranse that it was his professional duty to resolve, his eccentric local guide had pestered him with wild ideas about mile-high glaciers. In the urgent anxiety of those
days, he had paid them little mind. But now, as he cast his eye across the devastated valley with its unrecognizable, moon-like terrain, he must have realized that Jean-Pierre Perraudin was right. One couldn’t rely on the evidence of one’s senses or on mere common sense. The Earth was capable of radical and total transformation, a fact that required a great leap of imagination to accept. After the close-up, traumatic, life-changing experience of the Val de Bagnes debacle, Venetz was ready to make that leap.