What to Know
A mysterious boom (or booms) roused people in Philadelphia late Monday night.
It wasn't clear where the sound came from, though the National Weather Service said it may have been caused by frost quakes.
This is the second time in a week that people heard a mysterious boom during the night.
For the second time in a week, Philadelphians are asking, what went boom in the night?
Just like last Tuesday, a loud noise, or noises, just before 11 p.m. Monday night caused people to turn to social media to ask what it was. People described it as a boom, louder than a firework.
This time, some people claimed to hear a series of loud noises.
anyone in philly hearing loud booms? there was one like 3 minutes ago and then just 3 more....
— Elliot A (@Heyitselliota) February 5, 2019
I heard a single boom about 3 minutes ago in South Philly. It sounded big. Not like fireworks or gunshots. More substantial.
— Michael Hanisco (@michaelhanisco) February 5, 2019
NBC10 reached out to Philadelphia firefighters and police but they didn’t know of a source of the sounds that were heard from South Philadelphia to Spring Garden.
The National Weather Service told NBC10 Tuesday that the booms may have been caused by frost quakes.
Frost quakes, also known as Cryoseism, are loud, booming or cracking sounds that occur when large amounts of water freeze quickly underground and then rapidly expand. The soil and rocks underground are forced apart by the expanding water and lead to the booming sound.
"This is a natural phenomenon that happens after a fast, deep freeze like we experienced several times in the past few weeks," NBC10 First Alert Weather chief meteorologist Tammie Souza wrote.
Yet while the National Weather Service named frost quakes as the possible cause of the booms, it has not yet been confirmed.
Last week’s boom was heard as far away as New Jersey. This week’s boom seemed more confined. People’s theories covered everything from a meteorological event to a firework from the Midnight Lion Dance celebration for Chinese New Year’s in Chinatown.
Just like last week’s boom, the U.S. Geological Survey had no reports of an earthquake in the area.
The cause of last week’s boom was never determined.