As the ground shook across Mexico this week due to a 7.0 magnitude earthquake, mysterious blue and red flashes of light illuminated the sky, drawing comparisons on social media with a biblical apocalypse and frightening the masses who’d taken to the streets for safety.
The dazzling lights, which appeared during the quake on September 7 as though they were shot from the ground like fireworks, were observed from the southern coastal city of Acapulco, near the quake’s epicenter, all the way to the capital Mexico City, roughly 200 miles away.
Videos by VICE
The exact cause of the luminous display is debated by scientists.
Among the most prominent theories is that the flashes are an example of what’s commonly known as earthquake lights, or EQL. Instances of this phenomenon have been recorded for hundreds of years, in some cases occurring in the hours and minutes before noticeable seismic activity.
For centuries earthquake lights were dismissed as folktales or illusions, but in recent decades, with the advent of video cameras for surveillance or on smartphones, more evidence that suggests their existence has led scientists to take a closer look.
Differing hypotheses regarding the cause of the phenomenon have been proposed, “including the disruption of the Earth’s magnetic field by tectonic stress and the so-called piezoelectric effect, in which quartz-bearing rocks produce voltages when compressed in a certain way.”
A study published in 2014, however, theorizes that the lights occur when seismic activity causes certain kinds of rocks to release energy, which can manifest itself in short, blue flames that emerge from the ground, spheres of energy resembling ball lightning that can hover in the air for seconds to minutes, or the bright flashes of light that shoot out from the ground and appear to be what was observed in Mexico.
Since the kinds of rocks that produce earthquake lights only exist in certain environments, occurrences are rare. Following a devastating 8.1 magnitude earthquake in Mexico that hit four years before the most recent one, similar lights were observed.
Still, many remain skeptical, including the United States Geological Survey, which noted that
“Geophysicists differ on the extent to which they think that individual reports of unusual lighting near the time and epicenter of an earthquake actually represent EQL: some doubt that any of the reports constitute solid evidence for EQL, whereas others think that at least some reports plausibly correspond to EQL.”
Others suggest that the lights seen in the sky over Mexico were caused by electrical shortages and the explosion of transformers along the grid, or even regular lightning. It’s also possible that there were shortages, lightning and earthquake lights combining to produce the spectacular show. Further study will be necessary to come to a definitive conclusion.
Meanwhile, many in Mexico are on edge wondering if another earthquake could hit before the month’s end. An unusual amount of seismic activity has occurred in September, including many of the most notorious quakes in the country’s history. The coincidence has led to much speculation, and a torrent of memes, but there is no scientific reason for why earthquakes would occur at a certain point of the year.