The Year Without a Summer, 1816

The summer of 1816 was so cold that snow fell in parts of New England in June, damaging crops that had already begun to grow. Freezing temperatures returned during what should have been the warmest months of the year, and the bizarre weather affected parts of Europe as well. In New England, the phenomenon became known as “the year without a summer,” as well as “eighteen hundred and froze to death” and “the poverty year.”

The cause was eventually traced to Mount Tambora in present-day Indonesia, which erupted catastrophically in April 1815. The volcanic eruption sent enormous amounts of sulfur-rich material into the atmosphere, reducing incoming sunlight and contributing to cooling across the Northern Hemisphere. Catastrophic crop failures drove up food prices and contributed to hunger in parts of Europe and North America. 

There was nothing supernatural about the event, but to people experiencing snow and killing frosts in the middle of summer, the sudden disappearance of warm weather must have seemed otherworldly. Perhaps fittingly, it was during this famously cold and gloomy summer that author Mary Shelley began writing Frankenstein.

The Mary Celeste, 1872

In December 1872, the crew of the Dei Gratia encountered the Mary Celeste about 400 miles east of the Azores in Portugal. The latter ship was still seaworthy and carried food, water, and most of its cargo. But its lifeboat was gone, along with everyone aboard.

The 10 missing people included Captain Benjamin Briggs, his wife, their 2-year-old daughter, and seven crew members. The Mary Celeste itself showed some signs of disorder; one of its pumps had been dismantled, and water had accumulated in the hold. Yet most of the cargo was intact, including 1,700 barrels of high-grade alcohol. So what happened? 

Theories have ranged from piracy and mutiny to sea monsters and waterspouts. Writer Arthur Conan Doyle (of Sherlock Holmes fame) later turned the mystery into fiction in his short story “J. Habakuk Jephson’s Statement.” More plausible explanations have suggested that the crew feared an explosion or other danger involving the alcohol cargo and abandoned ship temporarily. Whatever happened, evidence has never established why 10 people left a seaworthy vessel and disappeared.

The Tunguska Event, 1908

On June 30, 1908, something exploded over a remote part of central Siberia with a force estimated to be equivalent to millions of tons of TNT. The blast flattened an estimated 500,000 acres of forest and knocked people off their feet many miles away, yet investigators found no conventional impact crater. 

There were around 700 eyewitnesses across 386 different locations, with many describing a brilliant flash and a tremendous explosion, while atmospheric disturbances were reported across parts of Europe. The event’s remote location made investigation difficult, and early theories ranged from a meteorite impact to a volcanic eruption. 

Scientists now believe the most likely explanation is an asteroid that entered Earths atmosphere and exploded several miles above the ground. The resulting airburst released enormous energy without striking the surface, explaining the absence of a crater. While the Tunguska event has a strong scientific explanation, its enormous scale and the lack of a visible impact site made it one of the great mysteries of the 20th century.

The Lead Masks Case, 1966

On August 20, 1966, the bodies of electronics technicians Manoel Pereira da Cruz, 32, and Miguel José Viana, 34, were discovered on Morro do Vintém, a hill in Niterói, Brazil. Both were wearing suits, waterproof coats, and homemade lead masks covering their eyes. There were no obvious signs of violence. Nearby, investigators found an empty bottle of mineral water and a notebook containing instructions telling the men to arrive at the site at a specific time, take capsules, and wait for a signal. The men had traveled to Niterói several days earlier, reportedly telling their families they were going on business.

The cause of death was never determined. Investigators found no clear evidence of poisoning, asphyxiation, or shock, and the available examinations could not establish what had happened to the men. The lead masks have inspired theories ranging from an experiment involving radiation to a planned encounter with extraterrestrial beings, but there is no evidence confirming any of the theories, and no radioactivity was found at the site. More than 50 years later, no one knows why the men went to the hill, what the masks were for, what was in the capsules, or what they expected to happen. 

The Taos Hum, 1990s

Beginning in the early 1990s, residents of Taos, New Mexico, began reporting a persistent low-frequency hum that sounded to some like a distant diesel engine, grinding machinery, or a low vibration. Only a small percentage of residents could hear it, however, while others standing nearby heard nothing.

The reports became widespread enough to attract the attention of New Mexico’s congressional delegation. In 1993, researchers from several laboratories and the U.S. Air Force investigated the phenomenon, using acoustic, seismic, and electromagnetic equipment to search for a physical source. One investigator reported hearing the hum himself, but the equipment failed to identify an external source that could account for the reports. 

Low-frequency environmental noise, industrial equipment, building vibrations, and individual differences in hearing have all been proposed as possible explanations. To this day, around 2% of town residents and visitors still experience the Taos Hum, and a single source has yet to be established.