Tambora: The Eruption That Changed the World (8 page)

Hence the recent development of an alternative index of volcanic measurement based on ice core data—the paleoclimatologist’s time travel machine. Historical accounts might reach back centuries, tree-ring data a little further, and geological evidence never see the light of day, but the new Ice-Core Volcano Index (IVI), through identification of sulfur isotope anomalies in polar and mountain ice, offers a trans-millennial measure of ash deposition in the earth’s remote glacial archives.
²⁴
Call it the volcanic Hall of Fame. Only eruptions that obtain stratospheric height, and hence climatic significance, find their immortal reward in the ice.

The status of Tambora according to the IVI is more complicated than under the old Smithsonian regime. Tambora’s ranking as the largest eruption of the second millennium has been challenged by partisans of other major eruptions of the Little Ice Age, including the 1258
Unknown, Mount Kuwae in 1452, and the 1600 eruption of Huaynaputina in Peru. The debate in the volcano-climate community over the relative magnitude of Holocene and Little Ice Age eruptions will surely continue, with fresh claims and counterclaims year by year. For the purposes of this book, however—standing as it does at the ceremonial eve of Tambora’s bicentenary and based on the scientific evidence currently available—I invite the reader to think of Tambora’s eruption as a thousand-year volcanic event, and among the very largest since human civilization emerged at the dawn of the Holocene twelve thousand years ago.

After years studying Tambora, when I ponder its relation to other volcanoes, my thoughts do not turn to Vesuvius, destroyer of Pompeii, nor to the great 1258 Unknown, purported trigger of the “Little Ice Age,” nor to Krakatau, volcanic darling of the Victorians. I think instead of a volcanic legend with far deeper historical DNA. The cataclysmic eruption of Santorini in the Aegean Sea in 1628 BC has been linked to the collapse of Minoan civilization, the legend of Atlantis, and the Israelites’ exodus from plague-ridden Egypt as told in the Bible.
²⁵
An awe-inspiring list, but the tale of Tambora will more than match it. The chapters that follow make the case for Tambora’s 1815 eruption as a world-historical event on the order of Santorini’s explosion three-and-a-half millennia ago, wreaking, through sinuous courses, comparable changes on global humanity and the totemic mind.

CHAPTER THREE

“THIS END OF THE WORLD WEATHER”

MONSTERS OF GENEVA

On the eve of the infamous lost summer of 1816, eighteen-year-old Mary Godwin took flight with her lover, Percy Shelley, and their baby for Switzerland, escaping the chilly atmosphere of her father’s house in London. Mary’s young stepsister, Claire Clairmont, accompanied them, eager to reunite with her own poet-lover, Lord Byron, who had left England for Geneva a week earlier. Mary’s other sister, the ever dispensable Fanny, was left behind.

The dismal, often terrifying weather of the summer of 1816 is a touchstone of the ensuing correspondence between the sisters. In a letter to Fanny, written on her arrival in Geneva, Mary describes—in hair-raising language that would soon find its way into her novel
Frankenstein
—their ascent of the Alps “amidst a violent storm of wind and rain.” The cold was “excessive” and the villagers complained of the lateness of the spring. On their alpine descent days later, a snowstorm ruined their view of Geneva and its famous lake. In her return letter, Fanny expresses sympathy for Mary’s bad luck, reporting that it was “dreadfully dreary and rainy” in London too, and very cold.
¹

Stormy northeasters are standard features of Genevan weather in summertime, careening from the mountains to whip the waters of the lake into a sirocco of foam. Beginning in June 1816, these annual storms attained a manic intensity not witnessed before or since. Mary’s famous second letter to Fanny is one of the most vivid documents we have of the violent volcanic weather in the Swiss summer of 1816: “An almost perpetual rain confines us principally to the house,” she writes on the first of June from Maison Chappuis, their rented house on the shores of Lake Geneva: “One night we
enjoyed
a finer storm than I had ever before beheld. The lake was lit up—the pines on Jura made visible, and all the scene illuminated for an instant, when a pitchy blackness succeeded, and the thunder came in frightful bursts over our heads amid the blackness.”
²
A diarist in nearby Montreux compared the bodily impact of these deafening thunderclaps to a heart attack.
³

The year 1816 remains the coldest, wettest Geneva summer since records began in 1753. That unforgettable year, 130 days of rain between April and September swelled the waters of Lake Geneva, flooding the city. Up in the mountains the snow refused to melt.
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Clouds hung heavy, while the winds blew bitingly cold. In some parts of the inundated city, transport was only possible by boat. A cold northwest wind from the Jura mountains—called
le joran
by locals—swept relentlessly across the lake. The Montreux diarist called the persistent snows and
le joran
“the twin evil genies of 1816.”
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Tourists complained they couldn’t recognize the famously picturesque landscape because of the constant wind and avalanches, which drove snow across vast areas of the plains.

On the night of June 13, 1816, the Shelleys’ splendidly domiciled neighbor, Lord Byron, stood out on the balcony of the lakeside Villa Diodati to witness “the mightiest of the storms” that he—well-traveled aristocrat that he was—had ever seen. He memorialized that tumultuous night in his wildly popular poem
Childe Harold’s Pilgrimage
:

The sky is changed—and such a change! Oh night,

And storm, and darkness, ye are wondrous strong …

From peak to peak, the rattling crags among

Leaps the live thunder! Not from one lone cloud,

But every mountain now hath found a tongue …

How the lit lake shines, a phosphoric sea,

And the big rain comes dancing to the earth!

And now again ’tis black,—and now, the glee

Of the loud hills shakes with its mountain-mirth,

As if they did rejoice o’er a young earthquake’s birth.
⁶

In Byron’s imagination, the Tamboran storms of 1816 achieve volcanic dimensions—like an “earthquake’s birth”—and take delight in their destructive power.

What caused the terrible weather conditions over Britain and western Europe in 1816–18? Why so much rain and so many destructive gales?

The relation between volcanism and climate depends on eruptive scale. Volcanic ejecta and gases must penetrate skyward high enough to reach the stratosphere where, in its cold lower reaches, sulfate aerosols form. These then enter the meridional currents of the global climate system, disrupting normal patterns of temperature and precipitation across the hemispheres. Tambora’s April 1815 eruption launched enormous volumes of long-suppressed volcanic rock and gases more than 40 kilometers into the stratosphere. This volcanic plume—consisting
of as much as 50 cubic kilometers of total matter—eventually spread across one million square kilometers of the Earth’s atmosphere, an aerosol umbrella six times the size of Mount Pinatubo’s 1991 cloud.

In the first weeks after Tambora’s eruption, a vast volume of coarser ash particles—volcanic “dust”—cascaded back to Earth mixed with rain. But ejecta of smaller size—water vapor, molecules of sulfur and fluorine gases, and fine ash particles—remained suspended in the stratosphere, where a sequence of chemical reactions resulted in the formation of a 100-megaton sulfate aerosol layer. Over the following months, this dynamic, streamer-like cloud of aerosols—much smaller in size than the original volcanic matter—expanded by degrees to form a molecular screen of planetary scale, spread aloft the winds and meridional currents of the world. In the course of an eighteen-month-long journey, it passed across both south and north poles, leaving a telltale sulfate imprint on the ice for paleoclimatologists to discover more than a century and a half later.

Once settled in the dry firmament of the stratosphere, Tambora’s global veil circulated above the weather dynamics of the atmosphere, comfortably distanced from the rain clouds that might have dispersed it. From there, its planet-girdling aerosol film continued to scatter shortwave solar radiation back into space until early 1818, while allowing much of the longwave radiant heat from the earth to escape. The resultant three-year cooling regime, unevenly distributed by the currents of the world’s major weather systems, barely affected some places on the globe (Russia, for instance, and the trans-Appalachian United States) but precipitated a truly drastic 5–6°F seasonal decline in other regions, including Europe.

The first extreme impact of a major tropical eruption is felt in raw temperature. But in western Europe, biblical-style inundation during the 1816 summer growing season wrought the greatest havoc. To understand the altered precipitation patterns fostered by volcanic weather, we must first grasp the principles of general circulation of the atmosphere. Because of the tilt of the Earth in relation to the sun and the different heat absorption rates of land and sea, solar insolation of the planet is irregular. Uneven heating in turn creates an air pressure gradient across the latitudes of the globe. Wind is the weatherly expression of these temperature and pressure differentials, transporting heat from the tropics to the poles, moderating temperature extremes, and carrying evaporated water from the oceans over the land to support plant and animal life. The major meridional circulation patterns, measuring thousands of kilometers in breadth, transport energy and moisture horizontally across the globe, creating continental-scale weather patterns. Meanwhile, at smaller scales, the redistribution of heat and moisture through the vertical column of the atmosphere produces localized “weather” phenomena, such as thunderstorms.