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The Great Earthquake

July 2024
15min read

When The Great Earthquake struck New England, learned men blamed everything from God’s wrath to an overabundance of lightning rods in Boston. Two hundred and twenty-five years later, geologists are at last discovering the true causes.

Shortly before dawn the five-inch pine spindle of the Faneuil Hall wind vane snapped, dislodging the thirty-pound gilded cricket that spun ten feet above Boston’s marketplace roof. Early risers first heard the baying of dogs, then the roar. Beneath the autumn moon, fifteen hundred chimneys swiveled and spewed bricks; the gable ends of brick houses that had survived the fire of 1747 collapsed onto cobblestone. As the contents of their homes toppled or migrated, families fled into the streets with shrieks attributed by one observer less to their embarrassment at “seeing their neighbors, as it were naked” than to their fears of confronting Judgment Day at last, and in nightclothes.

His Majesty’s regiments, camped at Lake George, a day’s march west of Vermont’s Green Mountains, felt the violence; so, presumably, did the one hundred and fifty French regulars gathered within scouting distance of the demoralized British troops. Newly arrived Samuel Chandler of Gloucester, Massachusetts, later recorded the time as four o’clock on the clear morning of November 18, adding, “2 soldiers died” in skirmishes that same day.

Settlers in Prince George County, Virginia, took note of it, while the captain of a westbound ship seventy leagues off the New England coast felt such a report beneath his vessel that he assumed he had struck a wreck or a sandbar. But when he lowered a lead, the measure sank to fifty fathoms—three hundred feet—in waters that soon began beaching dead fish miles away on the Massachusetts coastal tip of Cape Ann. Unaware, the captain and his crew had passed over the sea-covered epicenter of the first major earthquake in the recorded geological history of North America, and still one of the most powerful within historic memory.

The Cape Ann earthquake of 1755 shook the sleeping New World from Nova Scotia to South Carolina, evoking the greatest awe, damage, and contrition in the heavily populated northern colonies. “It was a terrible night,” wrote the Reverend Mather Byles of Boston, “the most so, perhaps, that ever NEW ENGLAND saw.” The tremors, followed by several more in ensuing days, signaled Divine displeasure to many. But they suggested Divine restraint once the colonies learned—about four weeks later—of the devastation of Lisbon by earthquake on November 1. At least thirty thousand died in the busy European port, many of them while worshiping in the churches on All Saints Day morning. The rest were swept away in the tidal wave that followed the violent shaking, which was felt as far north as Amsterdam.

From the rubble of Lisbon came the political ascent of the ruthless Marquês de Pombal, heightened religious recrimination, and Voltaire’s Candide, a biting satire of the prevailing optimistic creeds of such philosophers as Leibnitz. Out of the earthquake in the English colonies grew an earnest (if temporary) examination of contemporary morality. And, although a formal science of geology lay a generation in the future, the Cape Ann tremors left the inchoate discipline its first empirical accounting of a North American earthquake and provoked an energetic debate over the natural causes of such phenomena.

“The subject is curious, and at present engages the attention of many persons,” said John Winthrop IV, Harvard professor and occupant of only the second scientific chair in the colonies (the first was established in 1711 at William and Mary College). Eight days after the earthquake, which, in his words, had “spread terror and threatened desolation throughout New-England,” he attempted to reassure a nervous crowd in the college chapel, acknowledging that never had “so much damage [been] done to our buildings as by the last great shock.”

It was not the first earthquake in the continent’s known history. That record goes back to 1558 by way of the oral tradition of the native Pequot and Narraganset tribes in Rhode Island. Their members recounted their earthquake chronology to Roger Williams, the renegade province’s governor, after the first earthquake of the colonial era in 1638. “The younger natives are ignorant of the like,” Williams wrote to John Winthrop, founder of Boston and greatgrandfather of the Harvard professor, “but the ellder informe me that this is the 5t within these 4 score yeare in the land.” A Naunaumemoauke, as the natives called such a tremor, was inevitably the precursor to “either plague or pox or some other epidemicall disease,” Williams noted.

The “great and fearfull” earthquake of 1638, America’s first documented tremor, occurred on a sunny June afternoon throughout the English plantations. Recognized as coming from “the uninhabited parts of this Wilderness,” it is, in fact, now believed to have originated in the St. Lawrence valley.

Although the colonies proceeded to rock several times in the mid-1600’s, most notably in 1663, the crudest earthquakes of the epoch were occurring abroad. In 1692 Jamaica’s Port Royal was alternately shaken and inundated by an earthquake that opened huge chasms into which townspeople fell. “Some who were swallowed quite down, rose again in other Streets,” wrote the Reverend Thomas Prince, one of the chroniclers of later American earthquakes, “being cast up with great quantities of Water.” Americans read of other tremors that killed some ten thousand Neapolitans in 1688 or swallowed sixteen hills whole, supposedly, in Batavia, on the Island of Java, in 1699.

Sensitive to such a fate, American colonists responded to their next severe earthquake with something less than equanimity. The 1727 earthquake, now believed also to have been centered at sea off Cape Ann, was a brief but noisy event, beginning with “a pounce like great guns,” as a Newbury record notes.

But by the time the last aftershocks subsided, the worst reminders of a violent evening were broken stone walls and chimneys in New England and a pervading smell of sulfur, known better in those times as brimstone and widely believed to provoke earthquakes. “There’s certainly a trail of sulfur under the earth from Lima to Lisbon,” Voltaire’s demoralized Candide learned as the optimist Pangloss assessed the benefits of the Lisbon horror. The Reverend John Burt of Bristol, Rhode Island, adopted the Panglossian perspective about the American tremors. “What a happy Effect had the Earthquake in 1727,” he told his congregation, “to awaken the Secure, to reform the Vicious and to make all solicitous about their spiritual and everlasting Concerns.”

The effect must have worn off, because for about four minutes in 1755, the earth’s violent activity bound disparate American colonies of more than one million people in fear. It was the year in which General Edward Braddock had led British-American troops to an embarrassing July defeat at Fort Duquesne, nine months before the formal declaration of the French and Indian War. Preoccupied by the advances of their allied opponents, the colonists reflected somberly on the meaning of the November earthquake and catalogued its causes and effects, both physical and metaphysical.

The earthquake of 1755 announced itself at the waning edge of a calm, windless night. In Boston, cattle began to low and dogs to howl. Birds flew randomly in the moonlight. The vibrations approached with a sound “like the noise of many cartloads of paving stones thrown together.” A correspondent for the Boston Gazette recorded the time as 4:21 A.M., acknowledging that his own watch read 4:31, but that “most watches in Boston tend to be set at least 10 minutes too fast.”

Buildings shook as far north as Port Annapolis, Nova Scotia. The Reverend Joseph Smith of Portland, Maine, gauged the shock at two minutes, long enough to “seem as if it would shake the house to pieces, and then [it] threw down near one hundred bricks to our chimney, and did the same to many other chimneys in town.” The residents of Newington, in New Hampshire province, claimed that a “frightful chasm” two feet wide and sixty rods long—nearly one thousand feet—had opened near the town meetinghouse.

In Connecticut, Canterbury preacher James Cogswell identified a “dismal sound” before the onset of the “terrible ague,” adding, “Had the Shock been a few Degrees more heavy, or (perhaps), continued much longer in the same Degree, we might have been buried in the Darkness.” Benjamin Trumbull, future chronicler of Connecticut’s history, was a freshman at thirty-seven-year-old Yale College when he reflected “de terribeli teramotu” in his diary. “The earth seemed to wave like the waves of the sea,” he wrote, and, as buildings rocked, he saw students and villagers “rush from their couches with trembling and fear.”

The ground undulated visibly. In the Massachusetts coastal town of Scituate, where ten “cart loads” of white, floury earth spewed from chasms, citizens saw the earth “wave like the swelling of the sea,” while the sea itself engaged in a “commotion and roaring … no less terrible.” The sea’s response was not confined to the northern Atlantic, although mainland colonists would not know it until the January return of ships from the West Indies. Voyagers reported that at two in the afternoon of November 18, the sea withdrew from St. Martin’s harbor, leaving vessels aground in water normally twenty-four feet deep.

At the same time in Barbados, northeast of the Venezuelan coast, a violent tide began to ebb and flow from the island every six or seven minutes, not diminishing in energy until early evening. No one could recall the placid Barbados current “ever to set so strong as 2 miles in an hour,” reported Benjamin Franklin’s Pennsylvania Gazette. (The West Indies commotions may have had a different source, an earthquake that occurred on November 18 in Morocco, killing three thousand. Tradition has credited Cape Ann, however.)

The most pronounced damage from the American disruption occurred in New England, from New Haven to Portland. Accounts focused on Boston, probably because of its population of fifteen thousand, some of whom insisted they had heard Gabriel’s trumpet blow before the bricks began bouncing off their roofs. “The effects of the earthquake are very considerable in the town,” a reporter for the Boston Gazette wrote. The Reverend Charles Chauncey noted that, beyond the “breaking of our brittle wear and the bruising of our pewter,” the damage to structures in just one part of the region was “set, moderately computing, at about 50 thousand pounds in the common way we reckon money,” in a day when a barrel of West Indies rum cost three shillings sixpence, or a barrel of beef forty shillings.

Fortunately, the effects were worst where the concentration of residences was least—near the docks and warehouses on the “low, loose Ground, made by the Encroachments in the Harbour,” where one witness described his passage impeded by “large quantities of mortar and rubbish.” Although the large-scale filling of the waters around the original peninsula of Boston did not begin until 1804, the city had already begun to creep into the harbor with the building of wharves such as the fifty-four-foot-wide Long Wharf which stretched 1,586 feet into Town Cove. Atop the fill and pilings were a road and merchant houses vulnerable to earthquake. The original residential settlement of Trimountain, as Boston was called in 1630, covered Beacon Hill, which is geologically stable bedrock less responsive to earthquakes than silted sites.

“Never was such a scene of distress in New England before,” the voluble Thomas Prince reported. Dr. Prince, who managed to publish a small book on past earthquakes within a week of the Boston shock, quoted an acquaintance who went through the tremor while lying in bed “under the best Composure of Mind I could bring myself to.” When he emerged to examine the damage, he encountered a populace of “ghastly” faces, traced with “an Awe and Gloom … as would have checked the gay airs of the most intrepid Libertine among us.”

Disturbed twice more by the return of a trembling earth felt as far south as Pennsylvania on November 24 and December 19, and soon mindful of the Lisbon debacle, New Englanders took to prayer and fasting to ward off further manifestations of what the Bay Colony’s Lieutenant Governor Spencer Phips publicly pronounced God’s “righteous Anger against the heinous and provoking Sins of Men.” How directly Divine Providence participated in the events was a matter of considerable discourse.

The Reverend Mather Byles of Boston, who would be banished from his pulpit as a Tory after the Revolution, espoused the popular mechanistic philosophy of the day, under which cause and effect are considered intricately geared to events everywhere. If the world were analogous to a clock, the seventeenth-century chemist Robert Boyle observed, then God, who created the mechanisms and stood back watching them work, was the Divine Watchmaker. If the mechanistic attitude considered how an event occurred, the alternative philosophy of the day subscribed to the so-called teleological view, under which events are purposeful means to prescribed ends. The teleological approach is to ask, “What for?”

Thus, a teleological—and tedious—thirty-six-verse anonymous poem distributed after “the great earthquake” saw Divine intent, explaining:

In seventeen hundred and fifty-five,

When vice its empire did revive,

Consuming fire, a jealous GOD

Call’d on New-England with his rod.

But the mechanistic Reverend Byles proved more sanguine. “No Doubt natural Causes may be assigned for this Phaenomenon,” he told a group of colonists at Point Shirley, across Boston harbor. “An imprisoned Vapour too closely pent or too strongly compressed in the Caverns beneath, will thro, a natural Elasticity, abhor confinement, dilate and expand, swell and heave up the Surface of the earth, producing a tremor and Commotion.” Or, he conjectured, the mass of “Sulphureous and Combustible materials” underground meets with a spark and explodes. “How thin the Arch which interposes between us and a Furnace of Flame,” he exclaimed.

Elements of a nascent science of geology appear in the Americans’ analysis of their worst earthquake. Advances in chemistry, physics, and the concept of scientific method had followed the work of the Boyles and Newtons and Bacons of the seventeenth century, supporting a departure from such geologic convention as the biblical assertions that the earth was roughly eight thousand years old, that its crust had been shaped by the great flood, and that earthquakes—as Psalm 18 or Revelations 15 told it—were a fundamental tool of God’s wrath.

In 1749 Georges Leclerc, Comte de Buffon, of Paris had suggested an age of seventy-five thousand years for the earth, which he speculated had been created from solar matter after the collision of a comet and the sun. The long-standing assertion that the earth’s surface had been created from the condensation of minerals suspended in the Mosaic flood would soon face an opposing view that subterranean fire shaped the earth’s crust. Known as the Neptunists and the Vulcanists (or Plutonists), both schools were partly right.

Fire, and occasionally water, dominated the speculation about earthquake causes that arose in the colonies after the 1755 shocks, which produced the first attempts to probe such an event with scientific inquiry. Dr. Thomas Prince, who was pastor of Old South Church, acknowledged hypotheses by “the projecting Sort of Philosophers both ancient and modern” over “a central Concave of fire [or] a vast internal Abyss of Waters.” Then he projected his own theory, adding the phenomenon of electricity, lately described by Benjamin Franklin, to his list of earthquake causes.

God, Dr. Prince explained, had created an earth “of very loose Contexture,” in which existed numerous caverns filled with “Sulphurious, nitrous, fiery, mineral and other Substances such as those in the Clouds, which are the natural Causes of Thunder and Lightning.” The underground collision of these substances meant an explosion and, hence, an earthquake.

But earthquakes formed merely “a Twentieth Part of our imminent danger,” Prince announced. Citing Robert Boyle’s law of the pressure of gases, he warned that the “terrible atmosphere” blanketing the earth presses the ground with a weight of 2,592 pounds per square foot. After a subterranean explosion, he said, vapors escape, leaving a vacuum. The menacingly heavy air around us, “this astonishing Weight, besides that of the Earth, immediately bares away everything before it into the Space below.” Entire hills and cities had thus been pressed underground by the air.

Prince further refined his theory of electrical causes of earthquakes by suggesting that Boston had suffered worse shocks because of its abundance of lightning rods, then called iron points. The rods had been installed after 1751 at Benjamin Franklin’s suggestion, in a city that had last been ravaged by fire as recently as 1747. Prince suggested that they conveyed extra electricity into the earth from the sky and thus imperiled Boston.

Enter an incredulous Harvard professor. “Philosophy, like everything else, has had its fashions,” John Winthrop IV scoffed in response to Prince, “and the reigning mode of late has been to explain everything by ELECTRICITY.... Now, it seems, it is to be the cause of earthquakes.” The earth, he noted, was barred by simple laws of physics from creating electricity. And as for Prince’s lightning-rod theory, Winthrop answered, “I cannot believe that in the whole town of BOSTON, where so many iron points are erected, there is so much as one person, who is so weak, so ignorant, so foolish, or, to say all in one word, so atheistical, as ever to have entertained a single thought, that it is possible, by the help of a few yards of wire, to ‘get out of the mighty hand of GOD.’ ”

Winthrop, Hollisian professor of mathematics and natural philosophy at Harvard, continued his public tiff with Prince, whom he often referred to as “the Rev. Divine,” for several months. Colonists looked to the two of them for answers to the Cape Ann earthquake—which both men incorrectly believed to have come from the northwest. Winthrop, who had introduced Newton’s fluxions, or calculus, to the United States and opened the nation’s first experimental physics laboratory, was probably the most scholarly of colonists to contribute to the earthquake literature, if not the most prescient.

Flame and pent vapors, he believed, promoted earthquakes, a likelihood he supported by observing the abundance of tremors near volcanoes. Like Prince, he believed the quaking earth exhaled pent vapors, but, citing Newton, Winthrop suggested that the vapors might supply the atmosphere with “true, permanent air,” a mysterious but revitalizing substance.

Winthrop’s contribution to the imminent science of geology stems more from his careful, empirical descriptions and calculations of the Cape Ann earthquake events. By measuring effects, he carefully deduced the chronology and characteristics of the shock, applying physical maxims whenever he could. He documented the existence of both horizontal and vertical motion during a tremor, comparing the generation of earthquake “waves” to that of the vibrations of a struck musical chord, where an instrument’s strings bend broadly at first and then vibrate increasingly rapidly in returning to their stationary positions.

Winthrop told his Harvard Chapel audience that, like many others, he was forced to stay in bed, listening to the beams of his house crack in the violence, for at least the first two minutes of the earthquake. When he arose to seek his watch, it read 4:15 A.M. In examining his mantel clock, which he had earlier synchronized with his watch, he found that it had stopped at 35 seconds past 4:11. A test tube that Winthrop had placed inside the clock case “for security” after an experiment had toppled onto the clock’s pendulum, probably with the first tremor. Therefore, Winthrop concluded, the earthquake of 1755 lasted at least four minutes.

To determine the speed of the sway of the region’s buildings in the earthquake, he relied on the travels of a key tossed from his mantel and measured the distance that one of his chimney bricks had been thrown—thirty feet from a thirty-two-foot-high chimney. By calibrating the known speed of a falling object—thanks to Newton—he could show that his brick had probably traveled twenty-one feet in one second. The clue of the key, which had apparently not traveled so forcefully, suggested to him that the velocity of moving objects during an earthquake varied, depending on height.

From the northwesterly direction that the key flew, he ascertained that the course of the earthquake had been from northwest to southeast and calculated that it had occurred “at some considerable distance from this place,” since he had heard the earthquake about thirty seconds before he had felt it. If the speed of sound is about thirteen miles an hour, he reasoned, then earthquake vibrations traveled at some speed slower than sound.

He arrived, correctly, at a conviction that earthquakes were emitted in an undulating motion. During an aftershock felt the night after the November 18 tremor, Winthrop was sitting at a hearth with his feet on the bricks. As the tremor passed, his feet were lifted directly upward by a series of individual bricks, moving one at a time. “It was not a motion of the whole hearth together,” he explained to his audience, “either from side to side, or up and down; but of each brick separately by itself. Now as the bricks were contiguous, the only motion, which could be communicated to them separately, was in perpendicular direction...and this shock, I apprehend, was occasioned by one small wave of earth rolling along.”

But if Winthrop was the consummate observer of an earthquake in practice, a lesser known compatriot proved the more insightful theoretician. John Perkins was a Boston physician who, in his personal journals, freely indulged in scientific speculation, some of it—as in the origins of coal from plant matter—startlingly accurate. In 1758 he published an anonymous tract in the New American Magazine on the causes and effects of the 1755 earthquake, which he suspected had originated in the White Mountains of New Hampshire. Perkins recognized features in the earth and earthquakes that would not emerge as commonplace for generations.

Perkins’ suggestions were disarmingly reasonable. It was apparent, he noted, that because earthquakes often occurred near volcanic activity, there may be some relationship between heat and earthquakes. But that evidence had created a popular assumption that fire and rarefied vapors were a universal cause of earthquakes. In nonvolcanic regions, the concept was often supported by the occasional spewing up of sulfurous material. But any heat at these nonvolcanic sites may be misleading, he cautioned; it might be the effect of friction, of the earthquake itself, and not be a cause at all.

Instead, he said, “the settlement of high lands may sometimes be the first moving cause of earthquakes.” Imagine, he proposed, “what might be the consequence, by the infinitely greater force produced by the weight of a continent land, upon any quantity of matter put in motion under it.” Such settling was more likely to occur, he said, where caverns or channels “weaken the stability of the foundation supporting the earth.” Noting that earthquakes often occurred on continental coasts, he conjectured that they took place when the higher lands settled and forced the emergence of new coast land. The agitation of the sea that one saw during earthquakes was the effect of the spreading of the coast. Perkins’ theories are surprisingly close to the now commonplace awareness that stress, faults, and the collision of expanding tectonic plates contribute to earthquakes.

The Cape Ann earthquake of 1755 remained the premier in the United States until 1811, when a series of earthquakes struck the Mississippi River embayment at New Madrid, Missouri, and was followed by more than one thousand aftershocks. But on the East Coast, no earthquake would match the Cape Ann tremor until the 1886 Charleston, South Carolina, tremor that severely damaged that community. No earthquake east of the Rockies in the twentieth century has matched the Cape Ann disturbance or those two that followed.

At its sea-covered epicenter, the Cape Ann event (scientists now believe) would have been ranked 8.0 or 9.0 on a scale of 1.0 through 12.0, known as the modified Mercalli scale that measures the visible effects of earthquakes. On land, the earthquake might have registered a Richter scale magnitude of 6.0. The 1886 Charleston earthquake has been given a Mercalli intensity of 9.0 to 10.0, while the San Francisco earthquake reached 8.3 on a Richter rating with a Mercalli index of 11.0

Geologists are still puzzled by the dynamics of the 1755 quake. Unlike California—where the Pacific plate meets the North American plate, and essentially dives under it—the Eastern area is not at the earthquake-prone edge of such plates. But more than two hundred years after colonial scientists initiated the investigation, answers may be starting to emerge.

A study of New England’s magnetic field recently revealed a highly magnetic and circular underwater geologic formation at Cape Ann, probably a mass of gabbro, a rock denser than the granite known to surround it. Scientists suggest that this is a pluton, a huge rock cylinder descending into the earth. Similar plutons had been identified ashore—in the White Mountains—and when geophysicists compared notes, they found that plutons with matching characteristics existed in the same sites as the major historic earthquakes of the region. It may be that stress at the boundaries of these pillars caused not only the Cape Ann earthquake but also many of those that followed in the eastern United States.

Were an earthquake of the same intensity to recur at Cape Ann today, geologists have told the U.S. Congress, the damage, especially in the filled areas that now make up half of Boston, would be considerable, with lives lost. But in 1755, more sparsely settled Americans could give thanks for having been spared, newly mindful of the wages of sin. Considering the paucity of earthquakes for the next one hundred and thirty years, at least a few of them must have mended their ways.

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