The first known reports of them are from 89 BC, with spotty descriptions over the centuries.
Recently, they’ve been seen during foreshocks and the main earthquake in L’Aquila, Italy, in 2009, and as flashes of blue lightning over Wellington, New Zealand, in 2016.
One idea is that when igneous or metamorphic rocks are under stress, the molecular bonds break and release ionised oxygen that travels through the rock.
Plutonic rocks on the other hand cool very slowly, on the order of a million years or more for some deeply buried and insulated magmas.
After an 8.1-magnitude earthquake struck off the southern coast of Mexico on 7 September, videos of fuzzy green smears in the night sky went viral online.
Earthquake lights are a phenomenon so unusual that they border on myth.
In this line of thinking, some of these ions can create charged layers at or just below the surface, generating localised electric fields.
The strongest fields cause coronal discharges – brief bursts of visible light.
As igneous rocks cool, mineral crystals form following a specific sequence.