The isolated San Martin Tuxtla volcano is a

shield volcano A shield volcano is a type of volcano named for its low profile, resembling a shield lying on the ground. It is formed by the eruption of highly fluid (low viscosity) lava, which travels farther and forms thinner flows than the more viscous lava ...

which rises above the

Gulf of Mexico The Gulf of Mexico () is an oceanic basin and a marginal sea of the Atlantic Ocean, mostly surrounded by the North American continent. It is bounded on the northeast, north, and northwest by the Gulf Coast of the United States; on the southw ...

. It has had eruptions in historical times. It occurs in the Tuxtla volcanic field in

Veracruz Veracruz, formally Veracruz de Ignacio de la Llave, officially the Free and Sovereign State of Veracruz de Ignacio de la Llave, is one of the 31 states which, along with Mexico City, comprise the 32 Political divisions of Mexico, Federal Entit ...

Mexico Mexico, officially the United Mexican States, is a country in North America. It is the northernmost country in Latin America, and borders the United States to the north, and Guatemala and Belize to the southeast; while having maritime boundar ...

. Lavas from San Martin vary between

basanite Basanite () is an igneous, volcanic ( extrusive) rock with aphanitic to porphyritic texture. It is composed mostly of feldspathoids, pyroxenes, olivine, and calcic plagioclase and forms from magma low in silica and enriched in alkali metal ox ...

and

alkali basalt Alkali basalt or alkali olivine basalt is a dark-colored, porphyritic volcanic rock usually found in oceanic and continental areas associated with volcanic activity, such as oceanic islands, continental rifts and volcanic fields. Alkali basalt i ...

.Nelson, Stephen A. and Gonzalez-Caver, Erika; ''Geology and K-Ar dating of the Tuxtla Volcanic Field, Veracruz, Mexico,'' Bulletin of Volcanology, Volume 55, Issue 1-2, pp. 85-96
/ref> Locally the volcano is also known as Tiltépetl (Black Mountain in the Nahuatl language).

Morphology

San Martin forms a broad shield volcano, it rises to a height of 1680 m and is capped by a 1 km wide summit crater which is 150 m in depth. The crater contains two

pyroclastic cone Volcanic cones are among the simplest volcanic landforms. They are built by ejecta from a volcanic vent, piling up around the vent in the shape of a cone with a central crater. Volcanic cones are of different types, depending upon the nature and s ...

s that were the source of the large 1793 eruption. The flanks of the volcano are dotted with 250 pyroclastic cones and

maar A maar is a broad, low-relief volcanic crater caused by a phreatomagmatic eruption (an explosion which occurs when groundwater comes into contact with hot lava or magma). A maar characteristically fills with water to form a relatively shallow ...

s, some of which have been active in historical times. The volcano is currently densely forested.

Eruptions

1664 eruption: A large VEI 3 eruption occurred from the southeast flank. This led to an evacuation. 1793 eruption: A large VEI 4 eruption came from two pyroclastic cones in the summit, it produced widespread ashfall and lava flows that ran down the northeast flank. 1794-1796 eruption: A small VEI 2 eruption that continued for two years started in May, 1794.

References

* Kobs Nawotniak, S. E., J, Espindola and L. Godinez, ''Spatio-temporal evolution of the Tuxtla Volcanic Field,'' Journal of Volcanology and Geothermal Research, Volume 197, Issues 1–4, 30 November 2010, Pages 188–20
Abstract

External links

Los Tuxtlas Holocene shield volcanoes Volcanoes of Veracruz North American 1000 m summits {{volcano-stub