After more than fifty years, the mystery of the "Somerville Ghost" has been unraveled: it's all about geology (video).

Starting from the mid-19th century, there have been increasing stories about a ghost haunting the railway tracks between Charleston and Summerville in South Carolina (USA). There are several versions of this tale, but the essence is that a man who worked on the railroad was struck by a train and decapitated. After his death, his wife returned to the site with a lantern to search for her husband—her visits continued even after her own passing, as reported by IFLScience.

Throughout the 1950s and 1960s, and beyond, several strange sightings were reported on a nearby road parallel to the railway tracks. Witnesses described unusual lights that seemed to hover in the air. Eventually, the road, known as Old Sheep Island Road, became known locally as Old Light Road and turned into a hotspot for ghost hunters.

People who observed the lights typically described them as small, spherical, blue or green in color, although red or white spheres were occasionally seen. While the lights are generally visible from a distance, they have sometimes been seen moving toward the observer or even enlarging in size. One report mentioned that the lights were the size of a basketball and hovered in the air for several minutes.

In addition, there have been reports of ghostly apparitions in nearby homes and establishments, as well as other strange phenomena such as cars shaking, doors slamming, and whispers of voices with no discernible source.

Now, more than half a century later, seismologist Dr. Susan Haff, who works with the U.S. Geological Survey, believes she has uncovered the mystery behind the appearance of this enigmatic ghost in Charleston. Haff posits that all these sightings actually have a "common geological thread."

Dr. Haff suggests that the glowing orbs perceived as lanterns could be "earthquake lights." While there is no universally accepted theory explaining their cause, several ideas exist. One theory suggests they are caused by gas emissions from the Earth.

The gas emission hypothesis includes two possible mechanisms. Radon is an inert gas and thus does not ignite, but it could potentially be linked to the phenomenon of glowing discharge, where electrons move to an excited state and then fall back to their ground orbital shell. This typically occurs at low temperatures, close to freezing.

On the other hand, the gas release hypothesis suggests that they may be caused by the ignition of combustible gases in the presence of oxygen. According to Dr. Haff, the connection between the ghosts and the railway tracks made her think about sparks. However, this connection might have another explanation, such as the tendency of railroads to follow corridors that have been cut by faults.