Is it a sign of the apocalypse?

Earlier this month in San Diego, there was a large boom, the ground shook, and windows rattled.  But it wasn’t an earthquake, or a sonic boom from a supersonic plane.  In fact, nobody is sure what it was.

It isn’t the first time this has happened.

It happened in Maine in February. 

It happened in Alabama in January (see graphic). 

And last December, it happened in North Carolina, as well as the Gulf Coast and Whitby, England.

What’s going on? 

Seeing as how these events happened on the coast, here’s one explanation — "Seneca Guns":

The Guns of the Seneca are loud and largely unexplained booming sounds heard along the shores of Seneca Lake and nearby Cayuga Lake, the two largest of upstate New York’s Finger Lakes. Their sound has been described as being like distant, but inordinately loud, thunder while no clouds are in the sky large enough to generate lightning. Those familiar with the sound of cannon fire say the sound is nearly identical. The booms are occasionally sufficient to cause shockwaves that rattle plates. Early white settlers were told by the native Haudenosaunee (Iroquois) that the booms were the sound of the Great Spirit continuing his work of shaping the earth.

Other similar phenomena are found in coastal North Carolina, also called Seneca Guns, and in the Ganges valley of India, called Barisol Guns, as well as other sundry parts of the world. North Carolinians say their booms are the sound of pieces of the continental shelf falling off into the Atlantic abyss (but there is no geological evidence to support this).

One oft-advanced explanation is natural gas from decaying vegetation trapped beneath the lake bottoms suddenly bursting forth. This is plausible, since Cayuga and Seneca are two of the world’s larger and deepest lakes. However, the most frequent objection to this explanation is that such gas bubbles often burst into flame upon contact with the air and no such visible phenomenon has ever been reported in conjunction with the Guns of the Seneca. A more likely explanation is the explosive release of less volatile gases generated as limestone decays in underwater caves.

Current residents of the area around the lakes, given to less grandiose but no less picturesque descriptions than the Haudenosaunee and early white settlers, refer to the eruptions as "lake farts".

But even if the explanation can be attributed to "Seneca Guns", it begs the question: why the sudden rash of booms now?