By Anthony Milne
IN the wake of the eruption at Piparo, geologists
have stressed that "mud volcano" is a term applied to phenomena not
directly associated with the far more destructive explosions and lava
flows of true volcanoes, like the one now erupting in Monserrat.
These are unknown in Trinidad.
Mud volcanoes tend to be associated with petroleum
deposits. They are found in several parts of the world apart from
Trinidad, including the Caucasus, Australia and Venezuela.
George Higgins, in his History of Trinidad Oil, records
that one of Trinidad's oil pioneers, Walter Darwent, wrote in the
Chronicle newspaper of August 14, 1866, that his "expert" geologist,
Prof Ansted, "was convinced of a close connection between petroleum
and mud volcanoes, the latter being quite common in Trinidad."
It is therefore not surprising to find that a company
called Uroz Oilfields, with Beeby Thompson and Partners as consultants,
drilled two exploratory wells at Piparo in 1921. Higgins notes that
neither well "was considered to have been drilled deep enough
to the suspected oil pay." Another unsuccessful exploration well was
drilled there in 1923.
Geologists at Petrotrin's Geological Services Laboratory
in Pointe-?-Pierre visited the Piparo mud volcano on Friday to do
of tests and are to produce a report on the likely cause of the Piparo
eruption in a week or so.
They noted that records show that, more than 60 years
ago on November 3, 1930, an "eruption of similar magnitude" occurred
at the Tabaquite mud volcano, just north and east of Brickfield. The
"loud and violent" 1930 eruption lasted for 20 minutes and
spewed out at least 500,000 cubic yards of mud and associated debris.
Internal forces below the earth's surface which cause
mud volcanoes are believed to include the compression of clays and
differences in density and thickness of sediments causing movement.
Mud volcanoes are generally found where stratified
rocks with cores of mobile sediment, deposited rapidly and trapping
fold down from a crest. Pressure exerted on rock formations by deep
gas deposits, or gas generated closer to the surface,
can be an element in the formation of mud volcanoes.
Gas is often the driving force, pushing mud from
deep within the earth upwards towards the surface. The force is so
great it can
lift and break rock formations, so that pieces of rock are sometimes
thrown out with the mud when the volcano erupts.
Eruptions may be triggered by "external forces" such
as "movement along old fault lines", the Petrotrin laboratory's report
several of which have been mapped in the Piparo area in south-central
Trinidad, 12 miles east of Pointe-a-Pierre as the crow flies.
The Naparima Hill thrust fault passes through the
centre of the Piparo mud volcano, though it is not yet certain which
triggered last Saturday's eruption.
Fazal Hosein, 49, one of the Petrotrin geologists,
said visiting the Piparo volcano was an "eye-opener" and that there
evidence of "new movement along old fault lines".
According to a geological survey of Trinidad done
by geologist Hans Kugler and written up by John Saunders in 1954,
a copy of
which is lodged at UWI's library at St Augustine, mud volcanoes (produced
by "sedimentary volcanism") have been known
by local names including "bouffe", "morne" and "yard."
The word used by Amerindians was guaico, meaning
"mud-stream". There is of course a village called Guaico just west
of Sangre Grande, and an old, defunct oil well there.
The survey notes that mud volcanoes take various
forms in Trinidad: "mounds, cones, 'fladen' (flat cakes), streams
when the ejected mud is of the dry type, and bouffes, salsas, depressions,
when of the wet type".
Examples of mud volcanoes with cones occur at Piparo,
Tabaquite and Morne Diablo. Examples of volcanoes taking the form
of depressions are Lagon Bouffe at Guayaguayare and the Moruga Bouffe
("bouffe" being a French word which means "swelling").
Fladen mud volcanoes, "a type intermediate between
dry and wet," are found at Devil's Woodyard, near Princes Town, and
"The main feature controlling the shape is not the
amount of flow but the viscosity of the ejected mud lava," the survey
"which in turn depends on the content of the water, gas and/or oil
content of the source rock, usually an Oligocene clay."
Cones can be more than ten feet high and depressions
more than ten feet deep.
"The Piparo mud volcano, set upon the Naparima peneplain,"
Kruger's survey notes, "reaches an elevation of 365 feet"-150 feet
in relation to the surrounding land-"and covers some 425 acres."
This suggests that almost the entire hill on which
Piparo village is built must form the body of the volcano while the
at the top are the most recent vents. Since the eruption, the volcano
has increased in height by 15 or 20 feet.
The Morne Diablo mud volcano, "of perfect volcanic
shape", was 350 feet high at the time of the survey, visible from
and a landmark of the Southern Range. It covered an area of about
It was said to send out "mud lava streams two miles
According to the survey, "mud explosions recur at
regular intervals." It noted, as the Petrotrin geologists have, that
the last major
eruption occurred at Tabaquite in 1930, when the explosion "was heard
for miles around".
Mud volcanoes sometimes form temporary islands off
the coast. In November 1911 "Wilkey's Island", all of two and a half
acres, suddenly appeared off the south coast at Chatham, west of San
Francique. It was composed of blocks of clay and claystones,
as well as nodules of pyrites, and gave of a strong smell of hydrogen
In 1928 the phenomenon recurred but the island was
washed away by the sea within nine weeks. This has happened again
within more recent times, in 1964 and since.
The eruption at Piparo could perhaps stir new interest
in mud volcanoes, their origin and their destructive power.