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Mexico Volcanoes and Volcanics

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Map, Select Major Volcanoes of Mexico

Volcanism has had important impacts on the region. As was learned with the 1982 eruption of El Chichon, (and the even larger ca.260 A.D. eruption of Ilopango, in El Salvador), the region produces large explosive eruptions. ...

Most active volcanoes in this region occur in belts produced by subduction of Pacific oceanic crust beneath the southern edge of the North American Plate and the western edge of the Caribbean Plate. Large stratovolcanoes and silicic calderas are found here, but the region also contains many basaltic volcanic fields, particularly in the central valley of Mexico and along the Guatemala-El Salvador border. A few other active volcanoes in northern Mexico are related to extensional tectonics of the Basin and Range Province, which split the Baja California peninsula from the mainland.

The Colima volcanic complex is the most prominent volcanic center of the western Trans-Mexican Volcanic Belt. It consists of two southward-younging volcanoes, Nevado de Colima (the 4,320-meter-high point of the complex) on the north and the historically active Volcan de Colima at the south. A group of cinder cones of probable late-Pleistocene age is located on the floor of the Colima graben west and east of the Colima Complex. Volcan de Colima (also known as Volcan Fuego) is a youthful stratovolcano constructed within a 5-kilometer-wide caldera, breached to the south, that has been the source of large debris avalanches. Slope failure has occurred repetitively from both the Nevado and Fuego cones, and has produced a thick apron of debris-avalanche deposits on three sides of the complex. Frequent historical eruptions from Colima's summit crater have produced vertical pyroclastic columns, pyroclastic flows, and lava flows.

El Chichón is a small, but powerful andesitic tuff cone and lava dome complex that occupies an isolated part of the Chiapas region far from other Holocene volcanoes. Prior to 1982, this relatively unknown volcano was heavily forested and of no greater height than adjacent non-volcanic peaks. The largest dome, the former summit of the volcano, was constructed within a 1.6 x 2 kilometer summit crater, created about 220,000 years ago. Two other large craters are located on the SW and SE flanks. More than a half dozen large explosive eruptions have occurred since the mid-Holocene. The powerful 1982 explosive eruptions of high-sulfur, anhydrite-bearing magma were accompanied by devastating pyroclastic flows and surges and destroyed the summit lava dome. The eruptions created a new 1-kilometer-wide crater that now contains an acidic crater lake.

Volcanic eruptions are thought to be responsible for the global cooling that has been observed for a few years after a major eruption. The amount and global extent of the cooling depend on the force of the eruption and, possibly, its latitude. When large masses of gases from the eruption reach the stratosphere, they can produce a large, widespread cooling effect. As a prime example, the effects of Mount Pinatubo, which erupted in June 1991, may have lasted a few years, serving to offset temporarily the predicted greenhouse effect. ...

However, there is some confusion about the historical evidence that global cooling may be caused by volcanic emissions. Two recent volcanic eruptions have provided contradictory evidence on this point. Mount Agung in 1963 (Indonesia) apparently caused a considerable decrease in temperatures around much of the world, whereas El Chichon in 1982, seemed to have little effect, perhaps because of its different location or because of the El Nino that occurred the same year. El Nino is a Pacific Ocean phenomenon, but it causes worldwide weather variations that may have acted to cancel out the effect of the El Chichon eruption.

As observed after several eruptions, including Agung in 1963 (Indonesia) and El Chichon in 1982, stratospheric warming and lower tropospheric and surface cooling have been documented after the Pinatubo eruption. ...

A net cooling effect of approximately 0.3 degrees C was estimated as a result of the El Chichon aerosol (Angell and Korshover, 1983; Handler, 1989), but the overall potential cooling caused by the El Chichon cloud was moderated by warming assiciated with El-Nino-Southern Oscillation (Angell, 1988, 1990).

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In 1943 a cinder cone started growing on a farm near the village of Paricutin in Mexico. Explosive eruptions caused by gas rapidly expanding and escaping from molten lava formed cinders that fell back around the vent, building up the cone to a height of 1,200 feet. The last explosive eruption left a funnel-shaped depression called a crater at the top of the cone. After the excess gases had largely dissipated, the molten rock quietly poured out on the surrounding surface of the cone and moved downslope as lava flows. This order of events -- eruption, formation of cone and crater, lava flow -- is a common sequence in the formation of cinder cones.

During nine years of activity Paricutin built a prominent cone, covered about 100 square miles with ashes, and destroyed the town of San Juan. Geologists from many parts of the world studied Paricutin during its lifetime and learned a great deal about volcanism, its products, and the modification of a volcanic landform by erosion.

... The eruptive activity of Paricutin Volcano in 1947 demonstrated a "Vulcanian"-type eruption, in which a dense cloud of ash-laden gas explodes from the crater and rises high above the peak. Steaming ash forms a whitish cloud near the upper level of the cone.

Popocatépetl is a steep-sided volcanic cone located 55 kilometers east of Mexico City, Mexico, and 45 kilometers west of the Puebla metropolitan area. More than 30 million people live within view of the volcano and hundreds of thousands of people would be endangered by hazards associated with a large explosive eruption of the volcano. A major eruption would have serious consequences for people living in communities on the flanks of the volcano, and ash from such an eruption could also endanger aircraft using Mexico City international airport. About 30 eruptions have been reported in historical time, although documentation is poor. Most historical eruptions were apparently restricted to mild-to-moderate Vulcanian steam and ash emission. The latest significant activity took place from 1920-22. Popocatépetl is known to have produced a number of Plinian eruptions since the beginning of the Holocene.

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