My wife saw a puzzling sight in October 1994, in the Mekong River near
Nongkhai, Thailand, during a full moon, in the evening. Lights appeared under
the water for a few hundred metres along the Mekong River. They rose from the
bottom of the river and floated to the surface, then shot like missiles into the
sky and out of sight. They were the size of beach balls, and many flew out of
the water every few minutes, surfacing about 10 metres apart. I am told this
happens every year at the same time. Locals say it is caused by a serpent
releasing her eggs. Does anyone know of this phenomenon?
I read about the Mekong mystery with interest. In many respects it is similar to sightings of the ignis fatuus or will-o'-the-wisp which terrified English travellers in the Middle Ages and is found in the folklore of many different cultures. The ignis fatuus is a comparatively rare phenomenon which seems to result from the spontaneous combustion of marsh gases. For many years the active ingredient was thought to be a highly reduced compound of phosphorus--the hydride diphosphane which exerts a high vapour pressure at between 20 °C and -30 °C and spontaneously combusts in air at quite low concentrations. Earlier this century, scientists discounted the possibility that this compound could be formed by bacterial action, on thermodynamic grounds. But more recent work has shown that such reduced compounds do exist in decaying, phosphorus-rich organic matter. This can be seen in the so-called corpse candles reported in churchyards.
Even so, further explanation is required in the Mekong case, because the light there was seen rising below the water. Gases forming in the presumably anoxic muds of the river would not come into contact with sufficient oxygen for underwater combustion, and the diphosphane hypothesis may have to be discounted.
Some of the people who have experimented with these lights report seeing a "cold flame". There are several alternative theories to explain the phenomenon. For example, under low concentrations of oxygen, phosphorus vapour is luminescent and may easily form through diphosphane decomposition. Some microbiologists believe the phenomenon is caused by phosphorescent bacteria, a few species of which are thought to be soil-inhabiting. The dramatic exit of the gases as described by your correspondent is not without precedent and many remarkable descriptions are to be found in literature. I hold a record of European sightings and would welcome recent updates from readers. A British ignis fatuus distribution map is available to contributors.
Tunbridge Wells, Kent
Please send your records to Allan Pentecost c/o New Scientist: Mekong Mystery and we will forward the correspondence--Ed
The presence of the full Moon and the regular spacing of the lights would suggest to me an optical illusion.
Regular standing waves on rivers are not uncommon and may occur after heavy seasonal rain, for example. While they often remain in one place, they can move up and downstream if the river is tidal. Their height and spacing depend on flow and river bed topography.
The Moon, reflecting off these waves, can produce multiple reflections that might appear to move away from an observer, accelerating as the height of the wave decreases.
Boat bow waves can also be very long-lasting (they have been implicated in sightings on Loch Ness) and could produce similar effects.
[Archive: 20-27 December 1997]
I have heard of the Mekong lights, though I have not actually seen them. I worked in this area as a geologist, and being intrigued by reports of the lights, inquired after the phenomenon from both local farmers and eyewitnesses. I can offer the following extra information.
The lights not only occur in the part of the Mekong River that is referred to by your questioner but also in an adjacent area to the north, within Laos (in this area the Mekong River forms the national border between Laos and Thailand).
They are confined only to this small area and I have not heard of their occurrence anywhere else in Laos or Thailand. They arise both from the river and from rice paddies, many of which are still flooded at that time of year. The Thai/Lao name for them is the Nekha Lights--the nekha is a large fish which lives in the local waters and is seen in great numbers on the river surface at certain times of the year. Perhaps this is the serpent to which the original questioner refers. The lights are a famous and ancient annual phenomenon in both countries, and one to which the local people attach an important religious significance. Many Lao and Thai people travel to the area to try to see them, although the lights vary in their intensity and in some years are barely visible, if at all.
The lights have been filmed, and have also been shown on Thai television. The most intriguing aspect is that they occur only once a year, during the full moon in October for a very limited period (possibly only one night). The duration of a display is about 30 minutes, and there was a particularly dramatic show in 1996.
The Fortean Times recently ran a story on the lights, claiming that they are fireworks. The whole thing is apparently a hoax intended to attract tourists. I'll fill in more details when I find the article. I remain open minded