Monday,March 3,1997

Anatomy of a mud volcano

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 a series
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 water,
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 says,
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 fault
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 was
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 and terraces
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 in Cedros.

"The main feature controlling the shape is not the amount of flow but the viscosity of the ejected mud lava," the survey explains,
"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 bubbling holes
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 San Fernando
and a landmark of the Southern Range. It covered an area of about 425 acres.

It was said to send out "mud lava streams two miles long".

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 sulphide.

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.

Anatomy of a Mud Volcano  Interesting article from Internet Express,Trinidad,WI.
The Eruption I  Mud volcano engulfs Piparo, Feb.23rd, 1997
The Eruption II  When the Piparo bubble burst, March 2nd.1997
Still threatening  News of February 24th.1997
Once again, 2011  December 2011
Trinidad Express  Thanks to The Trinidad Internet Express
Mud volcano Lusi, Indonesia  See what happens when a mudvolcano doesn't stop!

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