Volcán de San Martín, part of the Tuxtla volcanic field, is a broad alkaline shield volcano that rises above the Gulf of Mexico.  The massive volcano, also known as San Martín Tuxtla, is elongated in a NW-SE direction and is capped by a 1-km-wide summit crater.  The upper part of the 1650-m-high volcano is covered with dense tropical rain forests.  The summit and flanks of San Martín are dotted with more than 250 pyroclastic cones and maars.  Well-preserved cinder cones are abundant between the summit of the volcano and Laguna Catemaco on the SE flank.  Holocene cones in this area produced ash deposits that buried recently discovered stone pyramids.  The two largest historical eruptions of San Martín took place in 1664 and 1793.  The 1793 eruption occurred from two cinder cones in the summit crater and produced widespread ashfall and lava flows that extended 3.5 km down the NE flank.