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 (ELA) is not known for Orizaba. Snow on the south and southeast sides of the volcano melts quickly because of solar radiation, but colder 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 3.5 km (2.2 mi) north of the crater rim, has a surface area of about 9.08 km2 (3.51 sq mi) descending from 5,650 m (18,540 ft) to about 5,000 m (16,000 ft). 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 50 m (160 ft).
Below the 5,000 m (16,000 ft) in elevation on the north side of the volcano, the outlet glaciers Lengua del Chichimeco and Jamapa extend north and northwest another 1.5 km (0.93 mi) and 2 km (1.2 mi), respectively. The terminal lobe of Lengua del Chichimeco at 4,740 m (15,550 ft), having a gradient of only 140 m km−1 (26.5 ft/mi), 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 4,975 m (16,322 ft) and, after 2 km (1.2 mi) with a gradient of 145 m km− 1 (27.5 ft/mi), divides into two small tongues that end at 4,650 m (15,260 ft) and 4,640 m (15,220 ft). 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 dela Barba, are hanging cliff or icefall glaciers, reaching the tops of giant lava steps at 4,930 m (16,170 ft) and 5,090 m (16,700 ft), respectively. They then descend 200 to 300 m (660 to 980 ft) farther down into the heads of stream valleys as huge ice blocks but are not regenerated there. About 1 km (0.62 mi), Glaciar Noroccidental, a small outlet glacier 300 m (980 ft) long, drains away from the side of Gran Glaciar Norte at about 5,100 m (16,700 ft) and draws down the ice surface a few tens of meters over a distance of 500 m (1,600 ft), descending to 4,920 m (16,140 ft) with a gradient of 255 m km− 1 (48.3 ft/mi). Another 1 km (0.62 mi) still farther south, Glaciar Occidental breaks away from Gran Glaciar Norte west of the summit crater at about 5,175 m (16,978 ft) as a steep, 1 km (0.62 mi) long glacier having a gradient of 270 m km− 1 (51.1 ft/mi) that ends at 4,930 m (16,170 ft). From the southwest corner of the mountain, another outlet glacier, Glaciar Suroccidental, 1.6 km (0.99 mi) long, flows from Gran Glaciar Norte at 5,250 m (17,220 ft) with a gradient of 200 m km− 1 (37.8 ft/mi), which also ends at 4,930 m (16,170 ft) in a long smooth surface.
East of the summit cone, a separate steep niche glacier, Glaciar Oriental, 1.2 km (0.75 mi) long and having a gradient of 440 m km− 1 (83.3 ft/mi), flows down the mountainside from about 5,600 to 5,070 m (18,400 to 16,630 ft); it contains many crevasses and seracs and is the most difficult glacier to climb. Glacier Oriental had a surface area of about 420,000 m2 (4,500,000 sq ft) in 1958, which makes the total area of glaciers and firn field on Citlaltépetl about 9.5 km2 (3.7 sq mi). No earlier historical record of glacier tongue activity (advance or recession) 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.
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