POPOCATEPETL (Aztec popoca "to smoke," tepeti "moun tain"), a dormant volcano in Mexico 18° 59' 47" N., 33' I" W., which with the neighbouring 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 17,876ft., or 438ft. short of that of Orizaba. This elevation was reported by the Mexican geological sur vey in 1895, and as the Mexican Geographical society calculated the elevation at 17,888ft., it may be accepted as nearly cor rect. The bulk of the mountain consists of andesite, with some porphyry, obsidian, trachyte, basalt, and other similar rocks.
It has a stratified cone which shows 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 6o to 8oft. above the plain and extends i8,000ft. east to west with a breadth of 6,000ft. 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 foot hills a little above 8,000ft., and continues up the slope to an elevation of over 13,000f t. On the lower slopes the forest is corn posed in great part of the long-leaved Pinus liophylla, accom panied by deciduous oaks and a variety of other trees and shrubs. From about 9,5ooft. to 11,50oft. the Mexican "oyamel" (Abies religiosa) becomes the principal species interspersed with evergreen oak, arbutus and elder. Above this belt the firs gradu ally 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, ac
companied 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 com paratively short distance, consisting chiefly of tussocks of coarse grass, and occasional flowering plants, the highest noted being a little Draba. At about 14,5ooft. 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 Sep tember. The reflection of light from the snow is blinding. The rim of the crater is reached at an elevation of approximately 17,500f t. The crater is elliptical in form, 2,008 by 1,312ft., and has a depth of 1,657ft. below the summit of the highest pinnacle and 673ft. 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 smoul dering, are everywhere visible, intermingled with the snow and ice that fills the crevices and covers the ledges of the black rocks.
It is believed that Diego de Ordaz was the first European to reach the summit of Popocatepetl, though no proof of this re mains further than that Cortes sent a party of ten men in 1519 to ascend a burning mountain. In 1522 Francisco Montano made the ascent and had himself let down into the crater a depth of 400 or 5ooft. No second ascent is recorded until April and Nov., 1827 (see Brantz Mayer, Mexico, vol. ii.). Other ascents were made in 1834, 1848 and subsequent years, members of the Mexi can geological survey spending two days on the summit in 1895.