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Jorullo is a cinder cone volcano in the Michoacan-Guanajuato volcanic field. Jorullo has four smaller cinder cones which have grown from it. The vents of Jorullo are aligned in a northeast to southwest direction. Lava from these vents cover nine square km around the volcano. Later eruptions produced lavas that had higher silica contents making them thicker than the earlier basalts and basaltic andesites lavas. Jorullo's crater is about 1,300 by 1,640 ft (400 by 500 m) wide and 490 ft (150 m) deep.
Jorullo was a totally new volcano, born on September 29, 1759. Earthquakes occurred prior to this first day of eruption. Once it began erupting, it didn't quit for 15 years. Jorullo grew 820 ft (250 m) from the ground in the first six weeks. The eruptions were phreatic and phreatomagmatic. They covered the area with sticky mud flows, water flows and ash falls. All but the youngest lava flows were covered by this ash fall. Later eruptions were magmatic with neither mud nor water flows. This 15 year eruption was the only one Jorullo ever had, and was the longest cinder cone eruption known.
Source of Information
Luhr, James F. and Simkin, Tom, "Paricutin: The Volcano Born in a Mexican Cornfield," Geoscience Press, Phoenix, 427 pp., 1993.