MUD "VENT AT POOLE

Today, Friday November 28^th 1997, geologists C.Archie, R.Maharaj and Allan De La Bastide f visited the "vent" reported by Mrs. Meena Sharma in Poole. The following notes are based on a discussion with Mrs. Sharma, observations made, the geology of the area and the Piparo experience.

Report from Mrs. Sharma

On Saturday November 15th, "steam" was seen emanating from the ground in the vacant lot next to the Sharma property. The steam smelt like sulphur, and was emanating to a height of about 3 feet above the ground. At this point there was no hole in the ground. As the day progressed, a hole developed and gradually got deeper, until it was about 4 feet deep. In the hole mud was seen, which was hot and bubbling, and a light brown to "ash" colour. There was not any exceptional rainfall on this day or the day before. Activity died down and the mud gradually got cooler. On Wednesday November 19th, Dr. Paul Jackson from the Seismic Research unit visited the location. At this time the mud was still warm. On Saturday November 22nd, Mrs. Sharma's husband heard a "boom which sounded like it was coming from below the ground".

Observations by above mentioned Petrotrin geologists. Nov. 28th.

Hole is 6 - 8 inches in diameter and about 4 feet deep. The mud is at the bottom of the hole and is light brown in colour. The mud has a sulphur like odor, and is slightly hotter than lukewarm, abnormally warm for 4 feet down. There is a tieback cable for a TSTT pole, and this cable enters the ground about 1 foot from the hole surface. This cable was felt continuing into the hole. almost parallel with the hole. Mrs. Sharma reported that the TSTT pole and tieback cable were installed earlier this year, around April - May.

Evidence of old landslides was found in the immediate vicinity. This area is known for it's landslides, and there is a geological reason for this as will be discussed below. In Mrs. Sharma's backyard which is in the adjacent lot, there are small cracks parallel to the road which indicates that they are older cracks due to minor land slippage in the area. Behind her fence there is a coconut tree which has obviously fallen recently, probably due to land slippage. Mrs. Sharma reported that this tree fell about one week before the eruption of gas in the adjacent vacant lot.

Geology of the area and association with mud extrusion

The area is on a major thrust fault that extends to the WSW where it passes close to the Devils Woodyard area. The formation outcrop in the area is Lengua Rubble. The surface expression of this fault is a ridge. The combination of this ridge and the Lengua clay with rubble are ideal conditions for land slippage which is common in this area.

There is no mud volcano in this area on the surface geology maps. However, the structure and stratigraphy of the area are fairly well suited for mud and gas expulsion, i.e. Major thrust fault which dips into unstable Lengua clay, and possible land slippage before the event. However, there is no cross fault as is seen in the Devils Woodyard and at Piparo.

Recent work done on the Piparo volcano showed that violent extrusions of mud such as the Piparo eruption have historically occurred in mud volcanoes associated with the Nariva formation. Generally the mud volcanoes associated with the Lengua have been more passive due to it's less plastic nature.

Conclusions

This event was a short lived extrusion of gas in an area which is suited to this activity due to it's structure and stratigraphy. The heat of the gas indicates that it came from deep in the subsurface, and that it moved up the deep seated thrust fault quite rapidly. The reason that the gas extruded where it did was that the 3-4 foot hole that was dug in April-May for the TSTT pole tie-back acted as a conduit for the gas as it neared the surface of the ground. It is difficult to predict whether or not this activity will re-occur or escalate in the immediate future. Mrs. Sharma was given contact info for the Petrotrin geologists and asked to report any further unusual activity.

Alan de La Bastide

Comments or Questions?