Geology
Pico de Orizaba evolved in three stages, the most recent initiating about 16,000 years ago during the late Pleistocene and Holocene. Citlaltépetl consists of three superimposed stratovolcanoes and dome intrusions which are: Torrecillas (650–250 ka), Espolón de Oro (210– 16 ka), and Citlaltépetl (16 ka to present). The volcano was formed by thick andesitic and dacitic lavas that followed repetitive explosive eruptions and lava effusions which created the iconic cone structure. The volcano is currently dormant but not extinct. The latest eruption of the volcano occurred in 1846 with a magnitude of VEI 2. Previous eruptions occurred in: 1687, 1613, 1589–1569, 1566, 1555–1545,1539–1533, 1351, 1260, 1187, 1175, 1157, 220 AD, 140 AD, 90 AD, 40 AD, ~780 BC, ~1500 BC, ~2110 BC, ~2300, ~2500, ~2780, ~4690, ~6220, ~6710, ~7030, and ~7530. The most violent eruption in the volcano's history is thought to have occurred around 6710 BC reaching a magnitude of VEI 5 characterized by lava dome extrusion and pyroclastic flow.
The volcano's crater is elliptical with a transverse diameter measuring 478 m (1,568 ft) and a conjugate diameter measuring 410 m (1,350 ft). The crater has an estimated 154,830 m2 (1,666,600 sq ft) with a maximum depth of 300 m (980 ft). Pico de Orizaba is constantly covered by an ice cap consisting of several glaciers. An outlet glacier, known as Jamapa Glacier is located on the northeastern side of the peak; it has been a powerful force in shaping the volcano. The Jamapa Glacier is responsible for a significant portion of the geomorphologic evolution of the region surrounding the volcano.
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