Skyquakes are another sound heard around the world. From the River Ganges in India to the Sea of Japan, these mysterious booms sound like cannon fire rumbling down from the sky. They are commonly heard near water, occasionally rattling windows and plates. Some have been explained by military aircraft breaking the sound barrier, but that doesn’t account for reports of skyquakes heard as far back as 1824.

Scientists have come up with a few likely causes. Near coasts, the booms may be caused by enormous waves crashing against the cliffs. Sand dunes are also capable, through unexplained mechanisms, of producing sounds including, on rare occasions, large booms. Other options are meteors generating sonic booms as they speed into the atmosphere; shock waves caused by coronal mass ejections from the Sun smashing into the Earth’s magnetic field; distant volcano eruptions; far-off thunder redirected through the upper atmosphere; deep earthquakes making noise by cracking the crust; and gas belching up from underground vents beneath ocean or lake beds.

As with the Hum, it is likely that a combination of these explanations are the culprits.