From a snow-capped volcano at 5,636 m to a dry lake bed about 10 m below sea level, Mexico packs a huge vertical range into 1,972,550 km² of southern North America, the 13th-largest country in the world, bordered by the United States to the north and Guatemala and Belize to the southeast. Its core is the Mexican Altiplano, a high plateau framed by two long mountain chains, the Sierra Madre Occidental in the west and the Sierra Madre Oriental in the east. Across its middle runs the Trans-Mexican Volcanic Belt, which holds the highest summit, Pico de Orizaba; further south rise the Sierra Madre del Sur and the highlands of Oaxaca and Chiapas. Around the edges lie coastal plains, the long Baja California peninsula and the flat limestone Yucatán. The lowest point is Laguna Salada in Baja California. The main rivers are the Río Bravo (Rio Grande) along the US border and the Usumacinta and Grijalva in the wet southeast. Descending from the top of the country to the bottom crosses every one of those landforms.
Pico de Orizaba and the Trans-Mexican Volcanic Belt
The journey starts at 5,636 m on Pico de Orizaba, the Nahuatl Citlaltépetl or "star mountain", on the border between Veracruz and Puebla. It is the highest mountain in Mexico, the highest volcano in North America and the continent's third-highest peak after Denali and Mount Logan. It is also, after Kilimanjaro, the second most prominent volcanic peak on Earth, because it rises so far above the land around it. Its last eruption took place in the 19th century, and it is classed as dormant rather than extinct.
Orizaba stands at the eastern end of the Trans-Mexican Volcanic Belt, a band about 900 km long and 130 km wide that crosses the country from the Pacific near Colima to central Veracruz. The belt exists because the Cocos Plate is being pushed beneath Mexico along the Middle America Trench off the southern coast. The sinking ocean floor melts at depth, and the magma rises through the overlying crust to build volcanoes. The same collision makes the region one of the most seismically active on Earth: the magnitude 8.0 earthquake of September 1985, centred in the subduction zone off the Pacific coast, killed more than 4,000 people in Mexico City, over 300 km away.
Popocatépetl and Iztaccíhuatl
Heading west along the belt, the next giants are the twin volcanoes east of the capital. Popocatépetl, "smoking mountain" in Nahuatl, rises to about 5,400 m (published figures range from 5,393 to 5,426 m) some 70 km southeast of Mexico City. It is an active stratovolcano; renewed activity in 1995 and 1996 forced the evacuation of nearby villages, and by early 2001 heat and eruptions had removed its glaciers. A high saddle, the Paso de Cortés, links it to Iztaccíhuatl, the "white woman", 5,230 m high, whose four snowy summits resemble the head, chest, knees and feet of a sleeping woman. Iztaccíhuatl is the lowest Mexican peak with permanent snow and glaciers, and its first recorded ascent was in 1889. Our Popocatépetl volcano guide follows the active twin in detail.
Nevado de Toluca and Parícutin
Further west, about 80 km from Mexico City, Nevado de Toluca reaches 4,680 m at Pico del Fraile on the rim of a summit caldera 1.5 km wide. Two lakes, the Lago del Sol and the deeper Lago de la Luna, lie on the crater floor at about 4,200 m. The volcano may once have rivalled Popocatépetl before an enormous eruption around 25,000 years ago removed its top. The belt is still building new peaks: in 1943 Parícutin erupted from the cornfield of the farmer Dionisio Pulido in Michoacán, and over nine years of activity grew a cone 424 m high and buried two towns under lava.
The Valley of Mexico, Lake Chapala and the Southern Altiplano
Below the volcanoes, with a floor no lower than 2,200 m, lies the Valley of Mexico, a closed basin of about 9,600 km² that has no natural outlet for the water running off its mountains. Five shallow, linked lakes once covered roughly 1,500 km² of its floor, the largest being Lake Texcoco, and the island city of Tenochtitlan stood in the lake system when the Spanish arrived in 1519 to find about a million people in the valley. The Spanish rebuilt Tenochtitlan as Mexico City and over time drained the lakes to control flooding, and by the 20th century they had almost vanished; today the valley drains through artificial canals to the Tula River. Mexico City grew across the old lake bed, and overextraction of groundwater beneath it has made the city sink below the historic lake floor.
The valley is one of many basins on the southern Altiplano, the higher half of the plateau, which averages about 2,000 m and is studded with valleys formed by ancient lakes. Guadalajara lies in another of them. West of the capital the Lerma River rises from lagoons near Toluca at more than 2,600 m and flows about 750 km across Querétaro, Guanajuato and Michoacán to Lake Chapala. Chapala, at 1,524 m and 45 km southeast of Guadalajara, has been the country's largest freshwater lake since Texcoco dried; it covers about 1,100 km² but averages only 7 m deep, and so much Lerma water is drawn off upstream that no water has flowed out of the lake into its old outlet, the Río Grande de Santiago, for more than 30 years.
The Sierra Madres, the Northern Altiplano and Copper Canyon
North of the volcanic belt the plateau drops to the northern Altiplano, which averages about 1,100 m as it runs through Zacatecas and San Luis Potosí towards the Río Bravo. Narrow isolated ridges cross it, and it is pocked with closed depressions, the largest being the Bolsón de Mapimí. On either side the land rises again into the two Sierra Madres. The Sierra Madre Oriental runs about 1,350 km from the Big Bend of the Texas border to the volcano Cofre de Perote, averaging around 2,200 m. The Sierra Madre Occidental extends about 1,250 km from near the US border to the Río Santiago, averaging 2,250 m with peaks around 3,000 m.
The western range is cut by deep canyons. In southwestern Chihuahua, six rivers draining the Sierra Tarahumara have carved Copper Canyon, the Barrancas del Cobre, a system of six distinct canyons covering about 65,000 km². All six rivers join the Río Fuerte and empty into the Gulf of California. Douglas-firs grow on the plateau rims above 2,400 m, oak forest on the middle slopes and figs and palms in the humid canyon bottoms, and the Rarámuri people move between the cool heights in summer and the warmer canyon floors in winter. The Copper Canyon geography guide covers the individual barrancas.
South of the volcanic belt the mountains continue as the Sierra Madre del Sur, about 1,200 km along the Pacific coast to the low Isthmus of Tehuantepec, and the Sierra Madre de Oaxaca, which runs 300 km southeast from Orizaba itself. Beyond the isthmus, in Chiapas, the Grijalva River has cut the Sumidero Canyon, whose vertical walls reach 1,000 m over a 13 km gorge before the river reaches the Chicoasén Dam.
Down to the Coastal Plains, the Yucatán and Laguna Salada
The last descent is to the sea. Mexico has about 9,330 km of coastline, mostly on the Pacific and the Gulf of California, and narrow coastal plains on both sides of the Sierras. Water is badly distributed across them. Nearly 150 rivers drain the country, two-thirds to the Pacific, yet five rivers flowing into the Gulf of Mexico, the Usumacinta, Grijalva, Papaloapan, Coatzacoalcos and Pánuco, carry 52 percent of all surface water. Southeastern Mexico, with about 15 percent of the territory, has most of that water, while the north and centre, home to almost 60 percent of Mexicans, have under 10 percent. Where the Grijalva joins the Usumacinta in Tabasco, the Pantanos de Centla biosphere reserve protects 302,702 hectares of wetland, the largest protected wetland in North and Central America.
In the far north the Río Bravo, the Rio Grande to Americans, forms the border from Ciudad Juárez to the Gulf as part of a 3,145 km land boundary with the United States, but since the mid-20th century only about a fifth of its water reaches the sea. In the far east the Yucatán Peninsula, about 181,000 km², is low, flat and made almost entirely of porous limestone. Rain sinks straight through it, so its northern half has no rivers at all; instead thousands of sinkholes called cenotes open onto a freshwater lens floating above seawater. A semicircle of cenotes traces part of the buried Chicxulub crater, about 200 km across, left by the asteroid impact 66 million years ago that is linked to the extinction of the dinosaurs. Our Yucatán Peninsula guide explores that karst country.
The bottom of the journey lies in the northwest. Laguna Salada, 30 km southwest of Mexicali in the Sonoran Desert of Baja California, is a vast dry lake about 10 m below sea level, roughly 60 km long and up to 17 km wide between the Sierra de los Cucapah and the Sierra de Juárez. It sits in a graben linked to the San Andreas fault system, where the Pacific Plate slides northwest past North America; the same motion pulled Baja California away from the mainland and opened the Gulf of California. Significant rains can fill the basin completely, but when it is dry its exposed lake-bed sediments are notorious for dust storms whipped up by summer monsoon thunderstorms.
From that salt flat, the snows of Orizaba are more than 2,000 km away and more than 5,600 m higher, a measure of how much relief Mexico's tectonic plates have built.