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Mysterious detonations—booming noises apparently unrelated to thunder or earthquakes—are among the most widespread and puzzling phenomena of nature. Long before the days of dynamite or sonic booms, fishermen in the North Sea were familiar with mistpouffers, their name for the distant rumblings they heard on calm, foggy days. In India’s Ganges Delta, the Barisal guns have long been familiar. G.B.Scott’s 1896 account in Nature expresses well his puzzlement when
he tried to trace them:
The villages are few and far between and very small, firearms were scarce, and certainly there were no cannon in the neighborhood, and fireworks were not known to the people. I think I am right in saying I heard the reports every night while south of Dhubri, and often during the day ... more distinctly on clear days and nights.
I specially remember spending a quiet Sunday, in the month of May, with a friend at Chilmari, near the river-bank. We had both remarked the reports the night before and when near the hills previously. About 10 a.m. in the day, weather clear and calm, we were walking quietly up and down near the river-bank, discussing the sounds, when we heard the booming distinctly, about as loud as heavy cannon would sound on a quiet day about ten miles off, down the river. Shortly after we heard a heavy boom very much nearer, still south. Suddenly we heard two
quick successive reports, more like horse pistol or musket (not rifle) shots close by. I thought they sounded in the air about 150 yards due west of us over the water. My friend thought they sounded north of us. We ran to the bank, and asked our boatmen, moored below, if they heard them, and if so in what direction. They pointed south!
Albert G. Ingalls, who discussed these mysterious sounds in Science magazine in 1934, grew up with the sound of the “guns of Seneca Lake” in upstate New York but had no better luck as an investigator: “Their direction is vague, and like the foot of a rainbow, they are always somewhere else ''when the observer moves to the locality from which they first seemed to come.”
Similar noises are called either marina or brontidi in Italy; to Haitians they are the gouffre. Early settlers in the Connecticut River valley (where the towns of Moodus and East Haddam now stand) were told by the Indians that the sounds represented the Indian god’s anger at the English god. Unlike many other such noises, those heard in Connecticut often involved earth tremors as well:
The effects they produce, are various as the intermediate degrees between the roar of a cannon and the noise of a pistol. The concussions of the earth, made at the same time, are as much diversified as the sounds in the air. The shock they give to a dwelling house is the same as the falling of logs on the floor. The smaller shocks produced no emotions of terror or fear in the minds of the inhabitants. They are spoken of as usual occurrences, and are called Moodus noises. But when they are so violent as to be heard in the adjacent towns, they are called earthquakes.
None of the usual signs of earthquakes accompanied the Moodus noises, however, so it maybe questioned whether“ the concussions of the earth” were a cause or and effect of the atmospheric phenomena.
Scientific attempts to explain such sounds began in earnest in the 1890s, when a Belgian, Ernest Van den Broeck, collected hundreds of pages of testimony about mist-poeffers from Iceland to the Bay of Biscay. He also drew the attention of Sir George Darwin, Charles Darwin's son and an expert on the tides, to the problem. That led to publication of many more reports in physical and meteorological journals throughout the English-speaking world.
Soon there were almost as many explanations as there were names for the mysterious noises. Van den Broeck himself believed that the most likely causes were ''some peculiar kind of discharge or atmospheric electricity'' (in other words, thunder - but from clear skies?), while one of his colleagues, M. Rutot, thought the origin to be internal to the earth, comparing the noise to“the shock which the internal fluid mass might give to the earth’s crust.” The latter theory was barely plausible even at the time. Although the molten interior zones of the earth certainly transmit earthquake waves, the liquid rock, or magma, cannot possibly slosh around as Van den Broeck's colleague seems to have imagined.
Others suggested that because many of the noises were associated with coastal regions and river deltas, perhaps they came from occasional settling of the earth beneath the steadily accumulating weight of sediment washed to sea. Such settling, though, should have produced large and noticeable waves and probably tidal waves, or tsunamis, as well.
Rock bursts—the fracturing of boulders or subterranean strata as ancient stresses are relieved—were advanced as a possible cause, but rock bursts produce a higher-pitched noise than that of most of the reported cases—a crack rather than a boom. In any event, most of the areas where rock bursts are common are mountainous regions, where sharp temperature changes can add their effects, rather than lowlands such as the Ganges Delta.
Another theory was offered by Father Saderra Maso, who had studied earthquakes in the Philippines for years before turning his attention to the distant noises that his native parishioners attributed to waves:
It is a common opinion among the Filipinos that the noises are the effect of waves breaking on the beach or into caverns, and that they are intimately connected with changes in the weather, generally with impending typhoons. Father Saderra Maso is inclined to agree with this view in certain cases. The typhoons in the Philippines sometimes cause very heavy swells, which are propagated more than a thousand kilometers [away], and hence arrive days before the wind acquires any appreciable force. He suggests that special atmospheric conditions may be responsible for the great distances to which the sounds are heard, and that their apparent inland origin may be due to reflection, possibly from the cumulus clouds which crown the neighboring mountains, while the direct sound-waves are shut off by walls of vegetation or inequalities in the ground.
Father Saderra Maso may have been correct, but a theory that depends on distant typhoons, breaking ocean swells, special (unspecified) atmospheric conditions, reflection of sounds by clouds, and strategically placed hills could explain virtually anything.
Similarly, when residents of the northeastern coast of the United States heard booming noises from the Atlantic in the winter of 1977, they were told that a few cases could be traced to sonic booms from Concorde airliners and that the rest were probably more distant sonic booms carried hundreds of miles by special atmospheric conditions. Air layers of a certain temperature and density can unquestionably conduct sounds much farther than usual, just as they can produce mirages of scenes beyond the horizon. However, they are unlikely to last until a scientific investigation can be made, which makes them conveniently untestable as explanations.
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