The massive 8.2-magnitude earthquake that rocked Mexico earlier this week was enough of a phenomenon on its own, but the quake also had something of a fascinating side effect: mysterious lights in the sky.

Numerous videos have been cropping up on social media showing the flashes brighten the night sky above Mexico City, but the flashes aren't lightning coming from the clouds above, or even lights from planes.

The flashes are instead thought to have been caused by the earthquake itself. More specifically, the lights come from a particular type of rock. 

A study published in 2014 revealed these lights can come in many forms, such as bluish flames, orbs of light, or quick flashes that resemble lightning.

"In certain types of rocks this accumulation of stress can break up pairs of negatively charged oxygen atoms in the ground, allowing them to flow up to the surface as an electrical current through cracks in the rock," proposed Leila Ertolahti, adjunct professor in geology at Farleigh Dickinson University, to Gizmodo.

"If enough atoms are present they can ionise pockets of air and form a plasma, or charged gas, that emits light."

As interesting as the lights (and the way they formed) are, the earthquake that preceded them was the strongest one Mexico has faced in nearly 100 years, and the second environmental disaster to occur this week following Hurricane Irma.

At an 8.2 magnitude, tremors could be felt from over 966 km (600 miles) from the epicentre, and the number of reported casualties is climbing.

"The scariest part of it all is that if you are an adult, and you've lived in this city your adult life, you remember [the 1985 earthquake] very vividly," said Alberto Briseño, a 58-year-old bar manager in Condesa, to The New York Times.

"This felt as strong and as bad, but from what I see, we've been spared from major tragedy."

This article was originally published by Futurism. Read the original article.