Pico de Orizaba


Citlaltépetl, otherwise known as Pico de Orizaba, is an active volcano, the highest mountain in Mexico and third highest in North America, after Denali/Mount McKinley of the United States and Mount Logan of Canada. Pico de Orizaba is also the highest volcano in North America. It rises above sea level in the eastern end of the Trans-Mexican Volcanic Belt, on the border between the states of Veracruz and Puebla. The volcano is currently dormant but not extinct, with the last eruption taking place during the 19th century. It is the second most prominent volcanic peak in the world after Mount Kilimanjaro. Pico de Orizaba is ranked 16th by topographic isolation.

Toponymy

Pico de Orizaba overlooks the valley and city of Orizaba, from which it gets its Spanish name – literally "Orizaba's peak". During the colonial era, the volcano was also known as Cerro de San Andrés due to the nearby settlement of San Andrés Chalchicomula at its base.
Its Náhuatl name, Citlaltépetl, comes from ' and and thus means "Star Mountain". This name is thought to be based on the fact that the snow-covered peak can be seen year round for hundreds of kilometers throughout the region. This name is not, however, used by the contemporary Náhuatl speakers of the Orizaba area, who instead call it Istaktepetl, meaning 'White Mountain'. The name Citlaltepetl is now believed to have been invented by a Spanish speaker who was likely knowledgeable in Náhuatl, but was unfamiliar with the actual name of the mountain itself.
A third name, Poyauhtecatl''', which means "the one that colours or illuminates", has also been recorded. This name was given by the Tlaxcaltecs in memory of their lost country.

Topography

The peak of Citlaltépetl rises dramatically to an elevation of above sea level; it has a topographic prominence of. Regionally dominant, Pico de Orizaba is the highest peak in Mexico and the highest volcano in North America; it is also the third highest peak in North America after Denali and Mount Logan. Orizaba is ranked 7th in the world in topographic prominence. It is the second most prominent volcanic peak in the world after Africa's Mount Kilimanjaro, and the volcano is ranked 16th in the world for topographic isolation. About to the west of the port of Veracruz, its peak is visible to ships approaching the port in the Gulf of Mexico, and at dawn rays of sunlight strike the Pico while Veracruz still lies in shadow. The topography of Pico de Orizaba is asymmetrical from the center of the crater; the eastern face is the steepest side of the volcano and the northwestern face the most gradual side. The gradual slopes of the northwestern face of the volcano allow for the presence of large glaciers and provide the most traveled route for hikers traveling to the summit.

Glaciers

Pico de Orizaba is one of only three volcanoes in México that continue to support glaciers and is home to the largest glacier in Mexico, Gran Glaciar Norte. Orizaba has nine known glaciers: Gran Glaciar Norte, Lengua del Chichimeco, Jamapa, Toro, Glaciar de la Barba, Noroccidental, Occidental, Suroccidental, and Oriental. The equilibrium line altitude is not known for Orizaba. Snow on the south and southeast sides of the volcano melts quickly because of solar radiation, but lower temperatures on the northwest and north sides allow for glaciers. The insolation angle and wind redeposition on the northwest and north sides allow for constant accumulation of snow providing a source for the outlet glaciers. On the north side of Orizaba, the Gran Glaciar Norte fills the elongated highland basin and is the source for seven outlet glaciers. The main glacier extends north of the crater rim, has a surface area of about descending from to about. It has a slightly irregular and stepped profile that is caused in part by the configuration of the bedrock. Most crevasses show an ice thickness of approximately.
Below the in elevation on the north side of the volcano, the outlet glaciers Lengua del Chichimeco and Jamapa extend north and northwest another and, respectively. The terminal lobe of Lengua del Chichimeco at, having a gradient of only, is a low, broad ice fan that has a convex-upward profile, a front typical of almost all Mexican glaciers. The most distinct glacier is Glaciar de Jamapa, which leaves Gran Glaciar Norte at about and, after with a gradient of, divides into two small tongues that end at and. Both tongues terminate in broad convex-upward ice fans thinning along their edges. The retreat of these tongues prior to 1994 produced much erosion downstream and buried their edges by ablation rock debris.
The west side of Gran Glaciar Norte generates five outlet glaciers. From north to south, the first two, Glaciar del Toro and Glaciar de la Barba, are hanging cliff or icefall glaciers, reaching the tops of giant lava steps at and, respectively. They then descend farther down into the heads of stream valleys as huge ice blocks but are not regenerated there. About, Glaciar Noroccidental, a small outlet glacier long, drains away from the side of Gran Glaciar Norte at about and draws down the ice surface a few tens of meters over a distance of, descending to with a gradient of. Another still farther south, Glaciar Occidental breaks away from Gran Glaciar Norte west of the summit crater at about as a steep, long glacier having a gradient of that ends at. From the southwest corner of the mountain, another outlet glacier, Glaciar Suroccidental, long, flows from Gran Glaciar Norte at with a gradient of, which also ends at in a long smooth surface.
East of the summit cone, a separate steep niche glacier, Glaciar Oriental, long and having a gradient of, flows down the mountainside from about ; it contains many crevasses and seracs and is the most difficult glacier to climb. Glacier Oriental had a surface area of about in 1958, which makes the total area of glaciers and firn field on Citlaltépetl about. No earlier historical record of glacier tongue activity is known for Citlaltépetl's glaciers. Although the Gran Glaciar Norte ice cap is covered with snow, it is possible to see the seven outlet glaciers on the irregular west margin of the ice cap, especially Glaciar de Jamapa and Glaciar Occidental.

Climate

The climate of Pico de Orizaba, like the Sierra Madre Oriental, varies greatly due to the change of elevation and prevailing winds. Due to the latitude and the extreme rugged terrain the volcano experiences many microclimates. Vegetation varies from tropical at the lower elevations on the eastern face to alpine forests in the higher elevations.
Large amounts of precipitation fall on the eastern face of the volcano due to adiabatic cooling and condensation from the trade winds that bring moisture off the Gulf of Mexico. The eastern face is frequently covered by fog and low cloud cover. The climate of the eastern face varies from tropical at the lower elevations to subtropical highland at the higher elevations, with mild variation in temperatures and an average annual rainfall of.
Subtropical climates are found between above sea level with a regular rainfall all year long. Autumn and winter come with frequent freezes and light snow, but the snow on the south and southeast sides melt quickly due to solar radiation. The northern face is dominated by subtropical highland. The southern face mostly experiences a humid subtropical climate, with the highest annual temperatures in the month of April.
Due to katabatic winds the western side is dominated by steppe creating a rain shadow below above sea level. Although there are some areas on the western side that experience most of the area is semi-dry with temperate to warm temperatures and an annual precipitation average of. Vegetation here is grass and shrubs with few alpine species.
Between, where temperatures usually are between, a cold-summer version of the subtropical highland climate predominates. Over with an annual average low of, alpine tundra prevails to the summit; heavy snowfalls and blizzards are common throughout the year. Snow on the south and southeast melts due to solar radiation, but continually remains on the north and northwestern faces. Extreme cold dominates a surface area of approximately.

Geology

Pico de Orizaba evolved in three stages, the most recent initiated about 16,000 years ago during the late Pleistocene and Holocene. Citlaltépetl consists of three superimposed stratovolcanoes and dome intrusions: Torrecillas, Espolón de Oro, and Citlaltépetl. The volcano was formed by thick andesitic and dacitic lavas that followed repetitive explosive eruptions and lava effusions that 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 BC, ~2500 BC, ~2780 BC, ~4690 BC, ~6220 BC, ~6710 BC, ~7030 BC, and ~7530 BC. 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 and a conjugate diameter measuring. The crater has an estimated with a maximum depth of. 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 north-eastern 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.

Geography

Pico de Orizaba is located at 19°1′48″N 97°16′12″W, about west of the Gulf of Mexico and east of Mexico City, on the border between the states of Veracruz and Puebla. The volcano is approximately south of the Tropic of Cancer. Orizaba anchors the south-eastern end of the Trans-Mexican Volcanic Belt, a volcanic chain that runs from west to east across Central Mexico. A companion peak lying about six km to the southwest of Pico de Orizaba is the Sierra Negra, at. This subsidiary peak is significantly lower than its massive neighbour, but the road to the observatory on its summit is the highest road in North America.
Pico de Orizaba, as part of the Sierra Madre Oriental, forms a barrier between the coastal plains of the Gulf of Mexico and the Mexican Plateau. The volcano blocks the moisture from the Gulf of Mexico from saturating central Mexico and influences the climates of both areas. Both the state of Veracruz and Puebla depend on Pico de Orizaba for supplying fresh water. The largest river originating on the volcano is the Jamapa River.