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.
ALLAN
PENTECOST
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.
TIM DOWNIE
Ayr
[Archive: 20-27
December 1997]
(continued)
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.
PAUL
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
-Ian