Pico de Orizaba

Pico de Orizaba is the easternmost stratovolcano in the Trans-Mexican Quaternary volcanic belt. The volcano is located on a major normal fault that marks the Altiplano from the Mexico Gulf coastal plain. Cross-section of Pico de Orizaba from Cantagrel and others (1984). The oldest rocks from the volcano are 1.5 million years old. Most of the volcano is made of andesite. About 100,000 years ago the composition shifted to dacite and tephra and block and ash flows were produced by Plinian eruptions and the collapse of extrusive domes. The terminal cone is 1,500 m tall and 4,000 m in diameter.

Pico de Orizaba last erupted in 1687, producing a small volume of gray ash. Eruptions in 1537 and 1613 produced small block-lava flows. More common in the volcano's history are the repeated eruptions in Saint-Vincent type pyroclastic flows. This type of pyroclastic flow, named for the volcanoes on the island of Saint-Vincent, are the result of flows from summit craters produced by the backfall of ejecta from the margins of vertical eruption columns. Saint-Vincent type pyroclastic flows were common during the 1902 eruption of Mt. Pelee. At Pico de Orizaba, seven eruption produced pyroclastic flows in 12,900 ybp, 10,600ybp, 9,400 ybp, 7020 ybp, 6,200 ybp, 4060 ybp, and 3,400 ypb (ybp = years before present).

Because Pico de Orizaba has not erupted for centuries people might think itis not a hazardous volcano. A look at a simple geologic map (based on Cantagrel, 1984) tells a different story. Several eruptions in the last 13,000 years have sent pyroclastic flows down the volcano. These flows were often channeled into river valleys and towards population centers. These type of eruptions have happened every 1,000-2,000 years in the past. The last large eruption with pyroclastic flows was 3,400 years ago. Future eruptions will probably also include highly mobile pyroclastic flows. The black arrows show the paths of older Saint-Vincent type pyroclastic flows.The white arrow shows the path of the Chocoman nuee ardente. Dark stars mark dacite domes. Dark areas covered by ash and block Pelean nuee ardentes. Major streams shown in blue.

Sources of Information

Cantagrel, J.M., Gourgaud, A., Robin, C., 1984, Repetitive mixing events and Holocene pyroclastic activity at Pico de Orizaba and Popocatepetl (Mexico): Bull. Volcanol., v. 47, p. 735-748.

Hoskuldsson A, C Robin, 1993, Late Pleistocene to Holocene eruptive activity of Pico deOrizaba, Eastern Mexico. BV55, 571-587.

Simkin, T., and Siebert, L., 1994, Volcanoes of the World: Geoscience Press, Tucson, Arizona, 349 p.

Williams, H., and McBirney, A.R., 1979, Volcanoes: San Francisco, Freeman,Cooper and Company, 397 p.

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