Have you ever heard about the Seneca Guns? No? Then you are in for a real treat.
Read on to find out more about these, as yet, completely inexplicable booming sounds off the Carolina coastline.
What are Seneca Guns?
Seneca Guns are an enigmatic series of loud booming noises that are, from time to time, heard along the Carolina coastline. Similar booms are heard in the Northeast, and along the East Coast and West Coast, but the "Seneca Guns" are most commonly associated with Lake Seneca in the Finger Lakes region of New York.
The name itself is thought to come from the work of James Fenimore Cooper with his short story "The Lake Gun". This story featured similar sounds heard near Seneca Lake.
"It is a sound resembling the explosion of a heavy piece of artillery, that can be accounted for by none of the known laws of nature," Cooper wrote. "The report is deep, hollow, distant, and imposing. The lake seems to be speaking to the surrounding hills, which send back the echoes of its voice in accurate reply. No satisfactory theory has ever been broached to explain these noises."
The term has also historically been applied to similar sounds along North Carolina, South Carolina, and Virginia. One notable event occurred in 1886 near Charleston, South Carolina when a magnitude 6.9 earthquake was accompanied by well-documented booming sounds.
Such observations often describe a roaring sound accompanied by surface seismic activity across the region. During this particular event, aftershocks accompanied by "loud detonations" were also observed for weeks after the main event.
According to the United States Geological Survey (USGS), "In the United States, most reports of mysterious booms come from the Northeast and along the East Coast, but there have also been observations along the West Coast."
To those who have heard them, they are often described as sounding like thunder or cannon fire. These sounds are most often heard in coastal areas and are rarely, if ever, heard at sea.
On land, when the phenomena are observed, the land often seems to shake like a small earthquake. Similar phenomena have also been witnessed in other parts of the world, and have been noted on the coast of North Carolina for more than 150 years.
Some "Seneca Guns" events have been so powerful in the past that windows have been rattled and buildings have been shaken. However, the reverberations have never been strong enough to cause permanent damage to infrastructure or buildings.
The Seneca Guns can be heard at any time of the year, but they appear to be most common in Fall (autumn) or when there is a noticeable cooling off of the weather.
In fact, Seneca Guns seem to be more common "during temperature inversions, when cool, dense air near the ground creates a sound channel that sounds can reverberate against, creating the booms we hear at ground level," according to the Federal Point Historic Preservation Society.
Various explanations do exist, including underwater caves collapsing, angry ghosts, distant thunder reverberations, meteors entering the atmosphere, and parts of the continental shelf falling into the ocean.
However, it is important to note, that while some of these have been excluded, there is currently no widely accepted explanation for the noises.
Other Seneca Gun events from around the world
As previously mentioned, similar phenomena to the Seneca Guns have also been observed in other parts of the world. In the Midwestern USA, for example, accounts of "artillery"-like sounds were said to occur before and during the New Madrid earthquakes of 1811-1822.
These earthquakes were between magnitude 7.4 and 7.9, and booms were noted throughout the midwest that also coincided with temperatures of -20 Fahrenheit (-28 Celcius) or colder. For this reason, these quakes are often referred to as "icequakes" or "frost quakes".
According to the USGS, such quakes appear to be the result of shallow groundwater freezing and expanding, which results in the dramatic cracking of surrounding frozen rock and soil. While apparently dramatic, they are not generally recorded on seismographs.
For this reason, some explanations for the booms heard during cold snaps might be from the expansion of the ground and of house foundations and other structures in extreme temperatures.
Other similar events have been noted in the Western USA too. Booming sounds accompanied the 2001 earthquake swarm near the city of Spokane, and, in 1989. USGS seismologists noted muffled booming sounds (but no shaking) while working on Mammoth Mountain in California.
Outside of the Continental US, similar phenomena have also been witnessed and documented. For example, in 1857, anecdotal accounts exist from a magnitude 6.9 earthquake in Italy. According to witness statements, the earthquakes were described as both "explosive" and "rushing and rolling".
Other accounts of sounds from small- to moderate-size earthquakes also come from England. Between 1880 and 1916 similar accounts were collected and published in 1938. These observations included descriptions of booming, blowing wind, muffled sounds, and “an immense covey of partridges on the wing”.
But there are also accounts of booming noises that are not associated with earthquakes. Most of these tend to have natural causes, from lightning, storms, tsunami waves, meteors, and the movement of sand dunes.
Booming or explosive noises can also be the consequence of human activities like sonic booms, explosions, and construction work.
What causes the Seneca Guns?
At present, as previously noted, there is no scientific consensus for what causes the Seneca Guns, but interesting theories do exist. These range from everything from military jets breaking the sound barrier to underwater earthquakes.
One of the most persuasive explanations for the Seneca Guns comes from the United States Geological Survey (USGS). In 2005, they postulated that the most probable cause for the sounds is shallow earthquakes occurring offshore.
"Those on the East Coast have not been directly studied and explained, but we can deduce from observations and measurements in West Coast locations that at least some of the East Coast booms are associated with very small earthquakes. Small shallow earthquakes sometimes produce rumbling sounds or booms that can be heard by people who are very close to them.
High-frequency vibrations from the shallow earthquake generate the booming sound; when earthquakes are deeper, those vibrations never reach the surface. Sometimes the earthquakes create booming sounds even when no vibrations are felt," explains the USGS.
While seemingly plausible, they have not yet been able to correlate events with any actual seismic activity using seismographs.
In fact, in 2001, a seismograph was installed within a 1,300-foot (396m) borehole near Fort Fisher State Historic Site. The project, for one reason or another, was never able to record any results of seismic activity.
Another interesting explanation for the Seneca Guns has been provided by a Duke University study. Researchers came to the conclusion that the guns are likely of atmospheric origin.
According to their theory, the vibrations (and sound) come from above ground level, instead of below it.
Another interesting explanation comes from a recent annual meeting of the American Geophysical Union (AGU). Conducted by researchers at the University of North Carolina, they collated and compared historical accounts of the "guns" with data collected by the Earthscope Transportable Array.
This is a network of 400-atmosphere sensors and seismographs. It was launched in 2003 and the array migrates between 1,700 locations in the continental U.S.
While, once again, no conclusive explanation could be provided, it was postulated that they could be caused by bolides.
Bolides are space rocks that travel so fast that when they hit the Earth's atmosphere they explode -- often very dramatically. Another explanation could be the crash of large waves or thunder far offshore.
If the atmospheric conditions are just right, the sound could be amplified in a particular direction or localized areas.
While all of these explanations are fascinating in and of themselves, experts are yet to nail down an actual definitive explanation for the Seneca Guns.
Like most things in life, the cause is probably multifaceted with different, ostensibly similar events having one of several causes from human activity to exploding space rocks.
Hopefully, in time, more research and data will finally be able to explain this very strange phenomenon.