A luminous phenomenon preceding or coinciding with an earthquake, frequently mentioned in anecdotal accounts, but of which few scientific observations have been made. Various glows, streamers, and luminous spheres have been reported. Numerous speculative theories as to the origin of the light exist, including the escape of gas from the ground (see ignis fatuus) and corona discharges (similar to St Elmo's fire). Other suggestions are that the light may be the phenomenon known as triboluminescence, where the fracture of crystals produces a momentary glow, or caused by the piezoelectric effect, in which charges separate in response to mechanical pressure.
Subjects: Meteorology and Climatology.