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POPOCATEPETL (Aztec popoca “ to smoke,” tepetl “ mountain ”), a dormant volcano in Mexico in lat. 18° 59' 47” N., long. 98° 33' 1” W., which with the neighboring Ixtaccihuatl (Aztec “ white woman ”) forms the south-eastern limit of the great basin known as the “ Valley of Mexico.” As it lies in the state of Puebla and is the dominating feature in the views from the city of that name, it is sometimes called the Puebla volcano. It is the second highest summit in Mexico, its shapely, snow-covered cone rising to a height of 17,876 ft., or 438 ft. short of that of Orizaba. This elevation was reported by the Mexican geological survey in 1895, and as the Mexican Geographical Society calculated the elevation at 17,888 ft., it may be accepted as nearly correct. The bulk of the mountain consists of andesite, but porphyry, obsidian, trachyte, basalt, and other similar rocks are also represented. It has a stratified cone showing a long period of activity. At the foot of the eastern slope stretches a vast lava field—the “malpays ” (malapais) of Atlachayacatl—which, according to Humboldt, lies 60 to 80 ft. above the plain and extends 18,000 ft. east to west with a breadth of 6000 ft. Its formation must be of great antiquity. The ascent of Popocatepetl is made on the north-eastern slope, where rough roads are kept open by sulphur carriers and timber cutters. Describing his ascent in 1904, Hans Gadow states that the forested region begins in the foothills a little above 8000 ft., and continues up the slope to an elevation of over 13,000 ft. On the lower slopes the forest is composed in great part of the long-leaved Pinus liophylla, accompanied by deciduous oaks and a variety of other trees and shrubs. From about 9500 ft. to 11,500 ft. the Mexican “ oyamel,” or fir (Abies religiosa) becomes the principal species, interspersed with evergreen oak, arbutus and elder. Above this belt the firs gradually disappear and are succeeded by the short-leaved Pinus montezumae, or Mexican “ ocote ”—one of the largest species of pine in the republic. These continue to the upper tree-line, accompanied by red and purple Pentstemon and light blue lupins in the open spaces, some ferns, and occasional masses of alpine flowers. Above the tree line the vegetation continues only a comparatively short distance, consisting chiefly of tussocks of coarse grass, and occasional flowering plants, the highest noted being a little Draba. At about 14,500 ft. horses are left behind, though they could be forced farther up through the loose lava and ashes. On the snow-covered cone the heat of the sun is intense, though the thermometer recorded a temperature of 34° in September. The reflection of light from the snow is blinding. The rim of the crater is reached at an elevation of about 17,500 ft. Another description places the snow-line at 14,268 ft., and the upper tree-line a thousand feet lower. A detailed description of the volcano was published by the Mexican geological survey in 1895 according to which the crater is elliptical in form, 2008 by 1312 ft., and has a depth of 1657 ft. below the summit of the highest pinnacle and 673 ft. below the lowest part of the rim, which is very irregular in height. The steep, ragged walls of the crater show a great variety of colours, intensified by the light from the deep blue sky above. Huge patches of sulphur, some still smouldering, are everywhere visible, intermingled with the white streaks of snow and ice that fill the crevices and cover the ledges of the black rocks. The water from the melted snow forms a small lake at the bottom of the crater, from which it filters through fissures to the heated rocks below and thence escapes as steam or through other fissures to the mineral springs at the mountain's base. The Indian sulphur miners go down by means of ladders, or are lowered by rope and windlass, and the mineral is sent down the mountain side in a chute 2000 to 3000 ft. Some observers report that steam is to be seen rising from fissures in the bottom of the crater, and all are united in speaking of the fumes of burning sulphur that rise from its depths. That volcanic influences are still present may be inferred from the circumstance that the snow cap on Popocatepetl disappeared just before the remarkable series of earthquakes that shook the whole of central Mexico on the 30th and 31st of July 1909.

It is believed that Diego de Ordaz was the first European to reach the summit of Popocatepetl, though no proof of this remains further than that Cortés sent a party of ten men in 1519 to ascend a burning mountain. In 1522 Francisco Montaño made the ascent and had himself let down into the crater a depth of 400 or 500 ft. No second ascent is recorded until April and November 1827 (see Brantz Mayer, Mexico, vol. ii.). Other ascents were made in 1834, 1848 and subsequent years, members of the Mexican geological survey spending two days on the summit in 1895.