Earthquake light
From Wikipedia, the free encyclopedia
A earthquake light is a bizarre, luminous aerial phenomenon, similar in appearance to the aurora borealis, that appears in the sky at or near areas of tectonic stress, seismic activity or volcanic eruptions. They are especially visible at night.
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[edit] Appearance
The lights are most evident in the middle of an earthquake, although there are reports of lights that occurred after or even before the earthquake, as in the 1976 Tangshan earthquake. They usually have shapes similar to those of the auroras and are white to bluish in hue, but occasionally they have been reported to have a wider color spectrum. The luminosity is typically visible for several seconds, but there have been cases in which they lasted tens of minutes.
There have been also cases in which electromagnetic waves caused by the earthquake interfered with radio transmissions, such as during the Great Chilean Earthquake of 1960.
[edit] History
Records of earthquakes that were accompanied by lights can be found as far back as 373 BC in ancient Greek writings, that "immense columns of flame" foretold the earthquake that destroyed the cities of Helike and Bura. However, even in the early 20th century they were still considered a myth, until photographs of actual lights were taken in Japan in the 1960s.
[edit] Theories
One theory suggests that earthquake lights are a form of plasma discharge caused by the release of gases from within the Earth that somehow become electrically charged in the air. They take on a variety of color, size and shape and may be an explanation for some UFO sightings where eyewitnesses report bright spheres of light diving to the ground or shooting up into the sky at high velocity. Some of these lights can also linger in the air for a time before vanishing and can be very large. During the day, these plasmas may take a on a shiny metallic appearance and have been used to explain the mass UFO sightings above Mexico City in the 1990s. Reports further indicated that after the sighting, an eruption occurred in a nearby volcano, which was explained as the source of the objects seen in the sky.
[edit] Suspected causes
The cause of this phenomenon is unknown, but several explanations have been suggested:
- Sparks or gas ionisation due to a piezoelectric effect in quartz-bearing rock
- Frictional heating
- Exoelectron emissions
- Sonoluminescence
- Triboluminescence
- Generation and ignition of flammable gases either from pockets of natural gas or from rocks under enormous stress.
- Gas ionisation or electrical effects due to electrokinetics
- Separation of positive hole charge carriers that turn rocks momentarily into p-type semiconductors
