Tambora Erupts in 1815 and Changes World History [Excerpt]

In 1816 a remarkable thing happened—there was no summer weather in much of the Northern Hemisphere. This excerpt from The Year without Summer explains why

Courtesy of Jialiang Gao

From The Year without Summer, by William K. Klingaman and Nicholas P. Klingaman. Copyright © 2013, by the authors and reprinted by permission of Saint Martin’s Press, LLC.

JUST BEFORE SUNSET on April 5, 1815, a massive explosion shook the volcanic island of Sumbawa in the Indonesian archipelago. For two hours, a stream of lava erupted from Mount Tambora, the highest peak in the region, sending a plume of ash eighteen miles into the sky.

More than eight hundred miles away, Thomas Stamford Raffles, the lieutenant-governor of Java, heard the blast at his residence and assumed it came from cannon firing in the distance. Other British authorities on the island made the same mistake. Fearing a neighboring village was under attack, the commander of the city of Djogjokarta, in central Java, dispatched troops to repel the invaders. Officials along the coast interpreted the sounds as signals from a ship in distress, and launched rescue boats to look for survivors.

At Makassar on the southwestern tip of Sulawesi, 240 miles northeast of Tambora, the commander of the Benares, a cruiser of the British East India Company, reported “a firing of cannon” on April 5. The explosions appeared to come from the south; as they continued, “the reports seemed to approach much nearer, and sounded like heavy guns occasionally, with slighter reports between.” Assuming that pirates were in the area, the Benares put to sea and spent the next three days scouring nearby islands for any signs of trouble, but found nothing. Nearly five hundred miles farther to the east, the British resident on the island of Ternate heard “several very distinct reports like heavy cannon,” and sent another cruiser, the Teignmouth, to investigate. It, too, returned empty-handed.

British authorities might have been excused for assuming that the threatening sounds came from potential enemies rather than the earth itself. They were not yet accustomed to the frequent volcanic eruptions that plagued the Indonesian islands. Britain had gained control of Java and the surrounding islands less than four years earlier, when British troops overwhelmed a vastly outnumbered band of French defenders who themselves had held Java for only a short time, having taken it from the Dutch when France conquered the Netherlands in 1794. By the spring of 1815, neither the government in London nor the British East India Company was entirely certain that they wanted to keep the island, since the expense of administering and defending it had outweighed the commercial benefits thus far.

Responsibility for British policy on the scene lay squarely with Raffles himself. The son of a ship’s captain, Raffles—who actually was born at sea, off the coast of Jamaica—dreamt of a British maritime empire throughout South Asia, an “Eastern insular Empire” that would provide new markets for English cotton and woolen textiles, and a profitable supply of coffee and sugar for Europe. It was Raffles who had persuaded the governor general of India, Lord Minto, to seize Java in the first place. Raffles also hoped to use Java as an avenue to improve relations with Japan, which he viewed as a rising Asiatic power. Meanwhile, heeding Minto’s advice to “do as much good as we can” while governing Java, Raffles reformed the colonial administration of the island, limiting the powers of the great landowners over their tenants and ameliorating the worst abuses of slavery while banning the importation of slaves under fourteen years of age.

But Raffles’ interests in the region extended beyond politics and commerce. After years of study, he was sufficiently fluent in the Malay language to conduct discussions directly with local chieftains. He regularly employed botanists and zoologists to obtain—at his own expense—specimens of local flora and wildlife, some of which he had preserved in spirit and shipped back to Britain. In his capacity as president of the Batavian Society, dedicated to the study of Java’s natural history, Raffles frequently toured the island and recorded his observations of geological phenomena. Several weeks before Mount Tambora erupted, Raffles became the first European to ascend a nearby mountain known as Gunong Gede; by using thermometers to measure the difference in temperature between the base and the peak, Raffles and his companions determined that they had climbed at least seven thousand feet. “We had a most extensive prospect from the summit,” he subsequently wrote to a friend. “The islands all round were quite distinct and we traced the sea beyond the southernmost point of Sumatra; the surf on the south coast was visible to the naked eye.”

So Raffles’ scientific curiosity was piqued when the cannonlike explosions from the southeast continued throughout the night of April 5 and into the morning hours. Shortly after dawn, a light rain of ash provided evidence that a volcano somewhere in the region had erupted. Few suspected Mount Tambora. It was generally believed that Tambora was extinct, although natives living in the nearest village had reported rumblings from deep inside the mountain during the past year. Besides, few on Java believed that such powerful sounds could have come from a volcano several hundred miles away. As Raffles subsequently noted, “the sound appeared to be so close, that in each district it seemed near at hand, and was generally attributed to an eruption either from the mountains Merapi, Klut, or Bromo.”

As a fog of ash drifted across Java, the sun faded; the warm, humid air grew stifling, and everything seemed unnaturally still. The oppressive pressure, Raffles noted, “seemed to forbode an earthquake.” Over the next several days, however, the explosions gradually subsided. Volcanic ash continued to fall, but in diminishing quantities. Relieved, Raffles returned to his routine administrative duties.

*   *   *

FAR from Tambora and the island of Java, a different sort of shock greeted the rulers and citizens of Europe in April 1815: Napoléon had returned to Paris.

The Emperor had spent the past year ruling the island of Elba, a rocky, desolate piece of real estate of no discernible strategic importance off the coast of Italy. Sixteen miles long and only seven miles across at its widest point, Elba in the early nineteenth century was home mainly to goats, deserted ruins, a variety of vines and scraggly shrubs on arid hillsides, and approximately twelve thousand impoverished peasants with a well-deserved reputation for being “extremely irritable” and “almost universally ignorant.” Its primary natural resource was rocks. One French observer who visited Elba shortly before Napoléon’s arrival warned that the island’s unremittingly inhospitable topography was likely to “fatigue the senses and impart sensations of sorrow to the soul.”

Napoléon had been consigned to Elba by the victorious allied coalition of Britain, Prussia, Austria, and Russia shortly after abdicating the French throne on April 6, 1814. (Perhaps as an ironic jest, they allowed him to retain the title of “Emperor.”) But the Allied statesmen who gathered at Vienna to sort out the consequences of nearly two decades of war neglected to provide a jailer, or even an effective network of informants to keep them apprised of Napoléon’s movements. Encouraged by press reports of widespread popular disaffection with the restored Bourbon monarchy in Paris, Napoléon decided that his former subjects would welcome him back. And so on February 25, 1815, accompanied by slightly more than a thousand troops, forty horses, and four cannon, Napoléon sailed away from Elba unopposed.

Six days later he landed at Golfe Juan, about a mile west of Cannes. “Frenchmen! In my exile I have heard your complaints and your wishes,” he exclaimed. “I have arrived in spite of every obstacle, and every danger.” Napoléon marched north rapidly, opposition crumbling as his entourage expanded at every town. “Taking towns at his liking and crowns at his leisure / From Elba to Lyons and Paris he goes,” crowed Lord Byron, who admired Napoléon and fancied himself an English counterpart of the Eagle. Although many of Napoléon’s former subjects—particularly his troops—greeted him enthusiastically, others responded more warily. Their caution reflected the heavy costs of Napoléon’s previous quest for glory: more than 900,000 French soldiers dead, and a depleted national treasury now saddled with millions of francs of reparations due the Allies. Napoléon attempted to allay their anxieties by publicly disavowing any new imperial ambitions. “I want less to be sovereign of France,” he told the people of Grenoble, “than the first of her citizens.”

News of Napoléon’s flight reached Vienna on March 7. Stunned, the Allied representatives decided within hours to send troops to oppose Napoléon, but they also embargoed the news from France for several days until they were prepared to make a public statement. Several days later, they jointly declared that by reappearing in France, Napoléon had proved himself “an enemy and disturber of the peace of the world,” and that together, “the sovereigns of Europe would be ready to give the King of France and the French nation the assistance necessary to restore peace.”

King Louis XVIII would need all the help he could get. Twenty-two years after the execution of his brother, Louis XVI, few Frenchmen outside of a die-hard circle of royalists desired to return to the days of a pre-Revolutionary monarchy. Too much land belonging to the king, the aristocracy, and the church had been dispensed to too many members of the Third Estate to turn back the clock. Nor had a year of life under the restored Bourbon dynasty endeared King Louis to his subjects. Facing an immense national debt which he inherited from Napoléon, Louis’ ministers found it necessary to slash the army budget, cancelling contracts for military supplies and throwing nearly three hundred thousand soldiers out of work. The government also reduced spending on public construction projects while maintaining an oppressive array of taxes. As unemployment rose along with the price of bread, hungry citizens in Channel ports rioted against the shipment of grain to Britain. “We are really going on very badly,” wrote one government official, “and we must do better if we do not wish to perish completely.”

Louis himself engendered little personal loyalty, or even respect; a British bishop once said that the French king was “a man fit only to cook his own capons.” Fifty-eight years old and so grossly overweight that he could not sit on a horse, Louis abhorred hard work and delegated authority with alacrity. Despite a modest measure of charm in private conversations, Louis never developed a compelling public presence. Certainly he paled in comparison with the charismatic former emperor. As Napoléon hastened towards the capital in March, covering two hundred miles in six days, Louis grew increasingly anxious. Ominous strains of the incendiary Marseillaise rang through Paris streets; royal troops deserted en masse and went over to Napoléon; and newspaper editorials likened the situation to the eve of the Terror, when nobles and monarchists were slaughtered. Recognizing that, as one writer put it, “the Parisians love for their King has so died down that barely a spark remains,” Louis decided on the evening of March 18 to flee Paris.

Three days later, Napoléon entered the city without a shot being fired. By the first week of April, however, it was clear that the weary and impoverished French public lacked any appetite for ambitious schemes to restore the glory of the empire. Napoléon’s proposals for new taxes to fund a revitalized army met with widespread opposition. Visible signs of disaffection appeared; rallies in support of the emperor’s return clashed with demonstrations demanding his ouster. To bolster his defenses against the Allied assault he knew was coming, Napoléon issued orders on April 8 for a general mobilization of the French nation. Meanwhile, he assured the sovereigns of Europe (whom he formally referred to as “my brothers”) that he wanted nothing more than “the maintenance of an honourable peace.”

But more than anything else, France—and the rest of Europe—desperately needed a breathing space. A year earlier, the Marquis de Caulaincourt had written that “the need for rest was so universally felt through every class of society, and in the army, that peace at any price had become the ruling passion of the day.” Napoléon’s return from Elba only deepened the prevailing exhaustion. “Our objective is to make sure that our children have years of peace,” noted the Austrian general Karl Schwarzenberg, “and that the world has some repose. The Emperor Napoléon had shown all too plainly of late that he desires neither of these things.”

*   *   *

AROUND seven o’clock on the evening of April 10, Mount Tambora erupted once again, this time far more violently. Three columns of flaming lava shot into the air, meeting briefly at their peak in what one eyewitness termed “a troubled confused manner.” Almost immediately the entire mountain appeared to be consumed by liquid fire, a fountain of ash, water, and molten rock shooting in every direction. Pumice stones—some walnut-sized but others twice the size of a man’s fist—rained down upon the village of Sanggar, nineteen miles away. After an hour, so much ash and dust had been hurled into the atmosphere that darkness hid the fiery mountaintop from view.

As the ash clouds thickened, hot lava racing down the mountain slope heated the air above it to thousands of degrees. The air quickly rose, leaving behind a vacuum into which cooler air rushed from all directions. The resulting whirlwind tore up trees by the roots and swept up men, cattle, and horses. Virtually every house in Sanggar was flattened. The village of Tambora, closer to the volcano, vanished under a flood of pumice. Cascading lava slammed into the ocean, destroying all aquatic life in its path, and creating tsunamis nearly fifteen feet high which swept away everything within their reach. Violent explosions from the reaction of lava with cold seawater threw even greater quantities of ash into the atmosphere, and created vast fields of pumice stones along the shoreline. These fields, some of which were three miles wide, were light enough to float; they drifted out to sea where they were driven west by the prevailing winds and ocean currents. Like giant icebergs, the pumice fields remained a hazard to ships for years after the eruption. The British ship Fairlie encountered one in the South Indian Ocean in October 1815, more than 2,000 miles west-southwest of Tambora. The crew initially mistook the ash for seaweed, but when they approached they were shocked “to find it [composed of] burnt cinders, evidently volcanic. The sea was covered with it during the next two days.” As there was no land for hundreds of miles (and evidently being unable to believe that the pumice could have traveled that far) the crew attributed the field to an underwater eruption of unknown location.

At ten o’clock the magma columns—which now consisted almost entirely of molten rock and ash, most of the water having boiled away and evaporated—collapsed under their own weight. The eruption destroyed the top three thousand feet of the volcano, blasting it into the air in pieces, leaving behind only a large crater three miles wide and half a mile deep, as though the mountain had been struck by a meteor. Propelled by the force of the eruption, gray and black particles of ash, dust, and soot rose high into the atmosphere, some as high as twenty-five miles above the crumbling peak of the mountain, where the winds began to spread them in all directions. As they moved away from the eruption, the largest, heaviest particles lost their momentum first and began to fall back towards the ground. This gave the ash cloud the shape of a mushroom or an umbrella, with the still-erupting Tambora as the fiery shaft. The lightest particles in the cloud, however, retained their momentum and remained high in the air; some even continued to rise.

By eleven o’clock, the whirlwind had subsided. Only then did the explosions commence. At Bima, on the northeast coast of Sumbawa about forty miles east of Tambora, the British resident reported that the blasts sounded like “a heavy mortar fired close to his ear.” A rain of ash poured down upon the villages, heavy enough to crush the roofs of houses, including the resident’s, rendering them uninhabitable. Waves surged in from the sea, flooding houses a foot deep and ripping fishing boats from their moorings in the harbor, tossing them high up onto the shore. In place of dawn, there was only darkness.

On board the Benares, still moored at Makassar, sailors heard the explosions—far louder than those of the previous eruption—throughout the night. “Towards morning the reports were in quick succession,” noted the ship’s commander, “and sometimes like three or four guns fired together, and so heavy, that they shook the ship, as they did the houses in the fort.” As soon as a semblance of dawn broke, the cruiser again set sail southward, to determine the cause of the blasts.

But the sky troubled the Benares’s captain. “By this time,” he noted, “which was about eight A.M., it was very apparent that some extraordinary occurrence had taken place. The face of the heavens to the southward and westward had assumed the most dismal and lowering aspect, and it was much darker than when the sun rose.” What appeared to be a heavy squall on the horizon quickly took on a dark red glow, spreading across the sky. “By ten it was so dark that I could scarcely discern the ship from the shore, though not a mile distant.” Ash began to fall on the decks of the Benares. An hour later, nearly the entire sky was blotted out.

By this time, Tambora’s umbrella ash cloud extended for more than three hundred miles at its widest point. As the cloud spread, the heavier clumps of ash within it drifted to the ground, but the rest remained aloft. “The ashes now began to fall in showers,” the ship’s captain wrote, “and the appearance altogether was truly awful and alarming.” By noon, the darkness was complete, and the rain of ash—which one sailor described as a tasteless “perfect impalpable powder or dust” that gave off a vaguely burnt odor—covered every surface on the ship. “The darkness was so profound throughout the remainder of the day,” continued the commander, “that I never saw any thing equal to it in the darkest night; it was impossible to see your hand when held up close to the eye.” Ash continued to fall throughout the evening; despite the captain’s efforts to cover the deck with awnings, the particles piled as much as a foot high on many surfaces. At six o’clock the following morning, there was still no sign of the sun, but the accumulated weight of the ash—which one officer estimated at several tons—forced the crew to begin tossing the powder overboard. Finally by noon on April 12, a faint light broke through, and the captain was struck by the thought that the Benares resembled nothing more than a giant calcified pumice stone. For the next three days, however, he noted that “the atmosphere still continued very thick and dusky from the ashes that remained suspended, the rays of the sun scarce able to penetrate through it, with little or no wind the whole time.”

A Malaysian ship from Timor sailing through the region also found itself in “utter darkness” on April 11. As it passed by Tambora, the commander saw that the lower part of the mountain was still in flames. Landing farther down the coast to search for fresh water, he found the ground “covered with ashes to the depth of three feet,” and many of the inhabitants dead. When the ship departed on a strong westward current, it had to zigzag through a mass of cinders floating on the sea, more than a foot thick and several miles across.

On the island of Sumatra, over a thousand miles west of Tambora, local chieftains heard the explosions on the morning of April 11. Fearing a conflict had broken out between rival villages, they hurried down to Fort Marlborough, the British encampment in Bengkulu. Other tribal chieftains on Sumatra and the neighboring islands also assumed the sounds presaged some sort of invasion, but once they received reassurance on that score, they ascribed the explosions to supernatural causes. “Our chiefs here,” reported an official at Fort Marlborough, “decided that it was only a contest between Jin (the very devil), with some of his awkward squad, and the manes of their departed ancestors, who had passed their period of probation in the mountains, and were in progress towards paradise.”

At Gresik on eastern Java, natives decided that the blasts were the “supernatural artillery” of the venerated South Java Sea spirit queen Nyai Loroh Kidul, fired to celebrate the marriage of one of her children; the ash was “the dregs of her ammunition.” If so, her ammunition made most of April 12 utterly dark in the village. When the British resident in Gresik awoke that morning, he had the impression that he had slept through a very long night. Reading his watch by lamplight, he discovered that it was 8:30 A.M., and pitch-black outside from the cloud of ashes descending. He breakfasted by candlelight at 11:00 and thought he could see a faint glimmering of light, but at 5 P.M. he still could “neither read nor write without candle.” In the nearby village of Sumenep, ash fell about two inches thick, and “the trees also were loaded with it.”

A tsunami reached eastern Java around midnight on April 10–11, and tremors struck the central region of the island eighteen hours after the eruption. Between two and three in the afternoon of April 11, a European observer in the village of Surakarta (Solo) noticed “a tremulous motion of the earth, distinctly indicated by the tremor of large window frames; another comparatively violent explosion occurred late in the afternoon.… The atmosphere appeared to be loaded with a thick vapour: the Sun was rarely visible, and only at short intervals appearing very obscurely behind a semitransparent substance.” Surakarta remained in darkness for much of the following day, as well. Raffles, too, reported that even at a distance of eight hundred miles, “showers of ashes covered the houses, the streets, and the fields, to the depth of several inches; and amid this darkness explosions were heard at intervals, like the report of artillery or the noise of distant thunder.”

Twenty-four hours after Tambora erupted, the ash cloud had expanded to cover an area approximately the size of Australia. Air temperatures in the region plunged dramatically, perhaps as much as twenty degrees Fahrenheit. Then a light southeasterly breeze sprang up, and over the next several days most of the ash cloud drifted over the islands west and northwest of Tambora. By the time the cloud finally departed, villages within twenty miles of the volcano were covered with ash nearly forty inches thick; those a hundred miles away found eight to ten inches of ash on the ground.

Even a small quantity of ash could devastate plants and wildlife. One district that received about one-and-a-quarter inch of ash discovered that its crops were “completely beaten down and covered by it.” Dead fish floated on the surfaces of ponds, and scores of small birds lay dead on the ground.

By the time the volcano finally subsided, Tambora had released an estimated one hundred cubic kilometers of molten rock as ash and pumice—enough to cover a square area one hundred miles on each side to a depth of almost twelve feet—making it the largest known volcanic eruption in the past 2,000 years. Geologists measure eruptions by the Volcanic Explosivity Index, which uses whole numbers from 0 to 8 to rate the relative amount of ash, dust, and sulphur a volcano throws into the atmosphere. Like the Richter Scale for earthquakes, each step along the Explosivity Index is equal to a tenfold increase in the magnitude of the eruption. Tambora merits an Index score of 7, making the eruption approximately one thousand times more powerful than the Icelandic volcano Eyjafjallajökull, which disrupted trans-Atlantic air travel in 2010 but rated only a 4; one hundred times stronger than Mount St. Helens (a 5); and ten times more powerful than Krakatoa (a 6). Only four other eruptions in the last hundred centuries have reached a score of 7. Modern scientists identify and measure past eruptions using layers of volcanic debris found in ice cores, lake sediments, and other undisturbed soils. Each eruption has a distinct chemical signature that, along with conventional methods of carbon dating, can be used to associate each layer of volcanic material with a particular eruption.

It was also by far the deadliest eruption in recorded history. As soon as the volcano quieted, Raffles ordered the British residents to make a survey of their districts to ascertain the extent of the damage. The reports that reached him detailed a horrific picture.

Before the eruption, more than twelve thousand natives lived in the immediate vicinity of Tambora. They never had a chance to escape. Nearly all of them died within the first twenty-four hours, mostly from ash falls and pyroclastic flows—rapidly moving streams of partially liquefied rock and superheated gas at temperatures up to 1,000 degrees, hot enough to melt glass. Carbonized remains of villagers caught unaware were buried beneath the lava; fewer than one hundred people survived. “The trees and herbage of every description, along the whole of the north and west sides of the peninsula,” reported one British official, “have been completely destroyed.” Another found that in the area surrounding Mount Tambora, “the cattle and inhabitants were nearly all of them destroyed … and those who survived were in such a state of deplorable starvation, that they would unavoidably share the same fate.” One village had sunk entirely, its former site now covered by more than three fathoms (eighteen feet) of water. And the Raja of Sanggar confirmed that “the whole of his country was entirely desolate, and the crops destroyed.” The survivors of his village were living on coconuts, but even the supply of that food was nearly exhausted.

On April 19, the Benares reached Bima. The coastline was barely recognizable; what had been one of the most beautiful and regular harbors in Asia now was an obstacle course, littered with masses of black pumice stone, tree trunks burnt and splintered as if by lightning, and the prows of previously sunken ships which the ocean had thrown onto land. The village had only a small supply of rice to stave off starvation. When the Benares departed several days later, it sailed past Mount Tambora, which had been one of the highest peaks in the archipelago, often used by sailors as a landmark. Clouds of smoke and ash still obscured the volcano’s peak. Even at a distance of six miles, sailors could see patches of lava steaming along the mountainside.

A heavy rainstorm on April 17 had left the air cleaner and cooler, and probably saved a substantial number of lives on the more distant islands as the rain washed the ash off crops and provided fresh drinking water to help stem an incipient epidemic of fever. But nothing could save those closer to Tambora. Over the following month, thousands more perished—some from severe respiratory infections from the ash that remained in the atmosphere in the aftermath of the eruption, others from violent diarrhoeal disease, the result of drinking water contaminated with acidic ash. The same deadly ash poisoned crops, especially the vital rice fields, raising the death toll higher. Horses and cattle perished by the hundreds, mainly from a lack of forage. Lieutenant Owen Phillips, dispatched by Raffles to investigate conditions and provide an emergency supply of rice to the inhabitants, arrived in Bima several weeks after the eruption and reported that “the extreme misery to which the inhabitants have been reduced is shocking to behold. There were still on the road side the remains of several corpses, and the marks of where many others had been interred: the villages almost entirely deserted and the houses fallen down, the surviving inhabitants having dispersed in search of food.” In the nearby village of Dompo, residents were reduced to eating stalks of papaya and plantain, and the heads of palm. Even the Raja of Sanggar lost a daughter to hunger.

In the end, perhaps another seventy to eighty thousand people died from starvation or disease caused by the eruption, bringing the death toll to nearly ninety thousand in Indonesia alone. No other volcanic explosion in history has come close to wreaking disaster of that magnitude.

And yet there would be more casualties from Tambora. In addition to millions of tons of ash, the force of the eruption threw 55 million tons of sulfur-dioxide gas more than twenty miles into the air, into the stratosphere. There, the sulfur dioxide rapidly combined with readily available hydroxide gas—which, in liquid form, is commonly known as hydrogen peroxide—to form more than 100 million tons of sulfuric acid. The sulfuric acid condensed into minute droplets—each two hundred times finer than the width of a human hair—that could easily remain suspended in the air as an aerosol cloud. The strong stratospheric jet streams quickly accelerated the particles to a velocity of about sixty miles per hour, blowing primarily in an east-to-west direction. The sheer power of the jet stream allowed the aerosol cloud to circumnavigate Earth in two weeks; but the cloud did not remain coherent.

Variations in the wind speed and the weight of the particles caused some parts of the cloud to travel faster or slower than others, and so the cloud spread as it moved around Earth, until it covered the equator with an almost imperceptible veil of dust and sulfurous particles. It also began to spread north and south, albeit far more slowly. While it took only two weeks for the aerosol cloud to cover the globe at the equator, it was likely more than two months before it reached the North and South Poles.

Rather than a slow, steady broadening of the equatorial cloud into the Northern and Southern Hemispheres, the cloud expanded in fits and starts. As some pieces of the cloud were blown away from the equator, they were quickly caught up in the dominant stratospheric jet streams—which in May blow east to west in the Northern Hemisphere, and west to east in the Southern Hemisphere. The cloud soon began to resemble streamers or filaments, with small portions regularly pushed off the equator and into the middle latitudes in each hemisphere. Eventually, these filaments coalesced into a single, coherent cloud that covered Earth.

And there they remained. Had the aerosol cloud ascended only into the lowest part of the atmosphere, the troposphere, where clouds form, rain would soon have cleansed the ash from the air. But in the more stable stratosphere, conditions mitigate against the formation of clouds of water droplets. The coldest air already is at the bottom of the stratosphere, with warmer air above it, so air rarely rises from the troposphere into the stratosphere. With no rising plumes of warm air to carry moisture into the stratosphere, clouds almost never form; the stratosphere is drier than most deserts. With no clouds, there could be no rain to wash away the stratospheric aerosol veil. Only the slow action of gravity and the occasional circulation of air between the stratosphere and the troposphere could drag the droplets back to the earth. And so the extraordinarily fine sulfur particles from Tambora that reached the stratosphere remained suspended in the air for years, freely transported around the globe by the winds. By the winter of 1815–16, the nearly invisible veil of ash covered the globe, reflecting sunlight, cooling temperatures, and wreaking havoc on weather patterns.

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