Devil’s WoodyardIn mid-February, local inhabitants reported a mild shaking early in the mornin

Devil’s WoodyardIn mid-February, local inhabitants reported a mild shaking early in the morning as this site on the island of Trinidad woke up and began erupting mud. This is one of several mud volcanoes on the island of Trinidad, all produced as a consequence of the local geology.Trinidad sits just off the northern edge of South America and its geology is related to basins at the edge of that continent. Sediments shed off of South America have accumulated in basins offshore since the continent rifted apart from Africa over a hundred million years ago. Today, those sediments are being reworked by complex plate boundary systems in the Caribbean, including faults that accommodate subduction motion and strike-slip faults that move side to side.The island of Trinidad hosts several types of geologic units. The northern half of the island consists of older, Jurassic-aged sediments that have been lightly metamorphosed after being deeply buried. These rocks represent some of the oldest sediments shed off of South America after the continental rifting. The southern part of the island contains younger sediments, including Miocene-aged sediments important to the story of this mud volcano. The sediments at the southern tip of the island have been folded into anticlines and synclines by the tectonic processes in this area and these structures cut across the island. The island’s southwestern tip is also cut by a strike-slip fault called the Los Bajos fault.These Miocene-aged (20 million years old or so) sediments are the source of several mud volcanoes on Trinidad. First of all, ocean water is able to seep into them from above, where the water is warmed by the heat of the Earth. This warm water wants to rise, to convect upwards, bringing that heat with it. Furthermore, the sediments contain organic matter that, as it is heated, decays and breaks down into natural gas. If it is trapped by impermeable rocks above, this deeply buried gas can form a natural gas reservoir, but if it has a fracture to flow through it will also rise towards the surface.The mud volcanoes of Trinidad occur in two groups, both in the southern part of the island, and it has been hypothesized that the main pathway that the fluids use to come up to the surface is the Los Bajos strike-slip fault. This fracture has opened pathways through the rock that the warm water and gas seeping upwards will follow. The fluids then leave the trace of this fault and migrate along the crest of the folded rocks until they find a fracture that guides them to the surface, creating the mud volcano site.Many of these mud volcanoes sit around regularly bubbling, with small amounts of gas and fluid escaping on a normal day. When a large gas pocket gets trapped at depth, it can clog the system and build up pressure until it triggers a larger eruption, as happened in February at this site. In fact, there are records of a mud volcano eruption off the island’s south coast in 1911 that was so large it triggered the temporary formation of a new island, until the waves had a chance to wash away the mud.In 1997, a mud volcano on Trinidad named Piparo erupted violently and spewed mud over 60 meters high. That eruption caused the evacuation of several dozen nearby residents and destroyed a few houses in the process.-JBBImage source: CNC3 Televisionhttp://bit.ly/2FEnqWgReferences:https://www.youtube.com/watch?v=c55WLj–OSYhttp://bit.ly/2ow3Wvzhttp://bit.ly/2sZseCZhttp://bit.ly/2HPhcn1http://bit.ly/2HP4hBHhttp://bit.ly/2t8409J -- source link

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