| Volcanoes |
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| The Los Tuxtlas Volcanoes are an aberration on Mexico´s Gulf Coastal Plain. The volcanoes are separated from the nearest volcano in the belt running across the spine of Mexico to the west by about 230 km, and from the Central American Volcanic Belt to the southeast by over 300 km. contains San Martin Tuxtla volcano, one of Mexico´s historically active volcanoes. The eruptions creating Los Tuxtlas apparently bridged two geological ages, with most of the Sierra de Santa Marta having been dated to the Pliocene (app. 5-2 million years ago), with an overlay of the San Martin volcanoes having been dated to the late Pleistocene, beginning app. 2 million years and lasting to the present. The last certified volcanic eruption occurred in 1793. There are dozens of named volcanoes in Los Tuxtlas, best known are San Martin Tuxtla, Cerro Santa Marta, Cerro Mono Blanco, San Martin Pajapan and Cerro El Vigia. (Cerro means hill in Spanish). |
| Types of local Volcanoes |
| There are basically two types of volcanoes in Los Tuxtlas, cinder cones and shield volcanoes. Shield volcanoes The major Los Tuxtlas volcanoes are shield volcanoes. They are built almost entirely of fluid lava flows. Flow after flow pours out in all directions from a central summit vent, or group of vents, building a broad, gently sloping cone of flat, domical shape, with a profile much like that of a warrior's shield. They are built up slowly by the accretion of thousands of highly fluid lava flows called basalt lava that spread widely over great distances, and then cool as thin, gently dipping sheets. Lavas also commonly erupt from vents along fractures (rift zones) that develop on the flanks of the cone. Some of the largest volcanoes in the world are shield volcanoes. Cinder cones Many of the hills surrounding Catemaco are cinder cones. They are built from particles and blobs of congealed lava ejected from a single vent. As the gas-charged lava is blown violently into the air, it breaks into small fragments that solidify and fall as cinders around the vent to form a circular or oval cone. Most cinder cones have a bowl-shaped crater at the summit and rarely rise more than a thousand feet or so above their surroundings. Source: US Geodesic Service |
| The volcanic field |
| Los Tuxtlas put the San Andreas Fault to shame. The area is a hodgepodge of fault lines in all directions. |
| The San Martin side is much younger than the rest, and the chart makes it obvious how lava flow closed off the then valley of Catemaco and turned it into a lake. |
| The Fault Lines |
| CENAPRED, the Mexican disaster prevention agency, considers the San Martin area a high volcanic risk zone, but only began monitoring the volcano in 2007. The actual risk zones are in the north of the area, so I will not lose any sleep |
| Risk Factors |
| Links |
| Los Tuxtlas Geography Veracruz, México |
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